Logano SK645/SK745 - Buderus

Logano SK645/SK745 

Heat is our element 

Technical guide 

Issue 10/2010 

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Sie finden die Bilder auf 

der Referenzseite 14: 

Buderus Product groups. 

Anordnung im Rahmen: 

- Tops 

- Left sides 

Low temperature boilers 

Output range from 

120 kW to 1850 kW

Table of contents 


1 Low temperature boilers . . . . . . . . . . . . . . . . . . 4 

1.1 Types and output . . . . . . . . . . . . . . . . . . . . . 4 

1.2 Applications . . . . . . . . . . . . . . . . . . . . . . . . . 4 

1.3 Characteristics and special features . . . . . 4 

2 Technical description . . . . . . . . . . . . . . . . . . . . . 5 

2.1 Equipment level . . . . . . . . . . . . . . . . . . . . . . 5 

2.2 Heating water routing . . . . . . . . . . . . . . . . . . 6 

2.3 Hot gas routing . . . . . . . . . . . . . . . . . . . . . . . 6 

2.4 Dimensions and specification . . . . . . . . . . . 7 

2.4.1 Logano SK645 dimensions and 

specification . . . . . . . . . . . . . . . . . . . . . . . . . 7 

2.4.2 Logano SK745 dimensions and 

specification . . . . . . . . . . . . . . . . . . . . . . . . . 9 

2.5 Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 12 

2.5.1 Pressure drop on the water side . . . . . . . . 12 

2.5.2 Boiler efficiency . . . . . . . . . . . . . . . . . . . . . 13 

2.5.3 Standby loss and flue gas temperature . . 14 

3 Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

3.1 Burner selection . . . . . . . . . . . . . . . . . . . . . 15 

3.2 Burner requirements . . . . . . . . . . . . . . . . . . 15 

4 Regulations and operating conditions . . . . . 16 

4.1 Extracts from the regulations . . . . . . . . . . . 16 

4.2 Pressure Equipment Directive (PED) and 

Health & Safety at Work Act . . . . . . . . . . . 16 

4.2.1 Application range . . . . . . . . . . . . . . . . . . . . 16 

4.2.2 Categories in accordance with the 

Pressure Equipment Directive 97/23/EC 16 

4.2.3 Health & Safety at Work Act regarding 

steam and hot water boilers . . . . . . . . . . . 17 

4.2.4 Overview of the Health & Safety at Work 

Act [Germany] . . . . . . . . . . . . . . . . . . . . . . 17 

4.3 Operating conditions . . . . . . . . . . . . . . . . . 18 

4.3.1 Operating requirements . . . . . . . . . . . . . . . 18 

4.3.2 Operating conditions . . . . . . . . . . . . . . . . . 18 

4.4 Fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

4.5 Water treatment . . . . . . . . . . . . . . . . . . . . . 19 

4.5.1 Definition of terms . . . . . . . . . . . . . . . . . . . 19 

4.5.2 Prevention of corrosion damage . . . . . . . . 19 

4.5.3 Prevention of damage through scale 

formation . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

4.5.4 Requirements for fill and top-up water . . . 20 

4.5.5 Application limits for boilers made from 

ferrous materials . . . . . . . . . . . . . . . . . . . . 21 

4.5.6 Recording the amounts of fill and top-up 

water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 

2 

4.5.7 Calculation to determine the permissible 

amounts of fill and top-up water . . . . . . . . 23 

4.5.8 Chemical heating water additives . . . . . . . 23 

4.5.9 Combustion air . . . . . . . . . . . . . . . . . . . . . . 23 

5 Heating controls . . . . . . . . . . . . . . . . . . . . . . . . 24 

5.1 Logamatic 4000 control system . . . . . . . . 24 

5.1.1 Logamatic 4212 control unit . . . . . . . . . . . 24 

5.1.2 Logamatic 4321 and Logamatic 4322 

control units . . . . . . . . . . . . . . . . . . . . . . . . 24 

5.1.3 Logamatic4411 control panel system . . . . 24 

5.2 Logamatic telecontrol system . . . . . . . . . . 24 

6 DHW heating . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

6.1 Systems for DHW heating . . . . . . . . . . . . . 25 

6.2 DHW temperature controller . . . . . . . . . . . 25 

7 System examples . . . . . . . . . . . . . . . . . . . . . . . 26 

7.1 Information regarding all system examples 26 

7.1.1 Hydraulic connection . . . . . . . . . . . . . . . . . 26 

7.1.2 Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 

7.1.3 DHW heating . . . . . . . . . . . . . . . . . . . . . . . 27 

7.2 Safety equipment to DIN-EN 12828 and 

DIN-EN 12953-6 . . . . . . . . . . . . . . . . . . . . 27 

7.2.1 Requirements . . . . . . . . . . . . . . . . . . . . . . . 27 

7.2.2 Arrangement of safety equipment to 

DIN-EN 12828; operating temperature 

≤ 105 °C; shutdown temperature (high 

limit safety cut-out) ≤ 110 °C . . . . . . . . . . 28 

7.2.3 Arrangement of safety equipment to 

DIN-EN 12953-6; shutdown temperature 

(high limit safety cut-out) > 110 °C . . . . . 29 

7.3 Sizing and installation information . . . . . . . 30 

7.3.1 Boiler circuit pump in the bypass as shunt 

pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 

7.3.2 Boiler circuit pump as primary circuit 

pump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 

7.3.3 Low loss header . . . . . . . . . . . . . . . . . . . . . 33 

7.4 Single boiler system Logano SK645 and 

SK745 with boiler control unit . . . . . . . . . 34 

7.5 Single boiler system with Logano SK645 

and SK745 boilers: Logamatic Boiler and 

heating circuit control with hydraulic 

separation . . . . . . . . . . . . . . . . . . . . . . . . . . 36 


and SK745 with boiler and heating circuit 

control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 


and SK745 with boiler and heating circuit 

control as well as hydraulic balancing . . . 40 

6 720 646 816 (10/2010) – Technical guide Logano SK645 and SK745

7.8 2-boiler system with Logano SK645 and 

SK745 with boiler and heating circuit 

control plus hydraulic balancing . . . . . . . . 42 


SK745 with boiler and heating circuit 

control plus hydraulic balancing . . . . . . . . 44 


SK745 as well as Logano plus SB315 and 

SB615 gas condensing boilers with boiler 

and heating circuit control . . . . . . . . . . . . . 46 

8 Delivery and installation information . . . . . 48 

8.1 Delivery method . . . . . . . . . . . . . . . . . . . . . . 48 

8.2 Installation information . . . . . . . . . . . . . . . . . 48 

9 Installation location . . . . . . . . . . . . . . . . . . . . . 49 

9.1 General requirements of the installation 

room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 

9.1.1 Combustion air supply . . . . . . . . . . . . . . . . . 49 

9.1.2 Siting combustion equipment . . . . . . . . . . . 49 

9.2 Handling details . . . . . . . . . . . . . . . . . . . . . . 50 

9.3 Installed dimensions . . . . . . . . . . . . . . . . . . 51 

10 Additional equipment and accessories . . . . 52 

10.1 Additional safety equipment to 

DIN-EN 12828 . . . . . . . . . . . . . . . . . . . . . . 52 

10.1.1Safety equipment . . . . . . . . . . . . . . . . . . . . . 52 

10.2 Additional noise attenuating equipment . . . 54 

10.2.1Requirements . . . . . . . . . . . . . . . . . . . . . . . . 54 

10.2.2Boiler support with structure-borne noise 

insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 

10.2.3Flue gas silencer with sealing collar to 

insulate against structure-borne noise . . . 56 

10.3 Additional accessories . . . . . . . . . . . . . . . . 56 

10.3.1Welded flange . . . . . . . . . . . . . . . . . . . . . . . 56 

10.3.2Flue sealing collar . . . . . . . . . . . . . . . . . . . . 56 

10.3.3Cleaning equipment set . . . . . . . . . . . . . . . 56 

11 Flue system . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 

11.1 General requirements of the flue system . . 57 

11.2 Flue gas parameters . . . . . . . . . . . . . . . . . . 58 

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 


6 720 646 816 (10/2010) – Technical guide Logano SK645 and SK745 3

4 

1 Low temperature boilers 

1 Low temperature boilers 

1.1 Types and output 

With the Logano SK645 and SK745 Buderus offers low 

temperature boilers with outputs ranging from 120 kW to 

1850 kW. The Logano SK645 is available with outputs 

ranging from 120 kW to 600 kW, the Logano SK745 

covers the output range from 730 kW to 1850 kW. 

These boilers feature reversing combustion to 

DIN-EN 303 for oil or gas. They are suitable for fuel oil EL 

to DIN 51603-1, natural gas or LPG to DVGW G 260. 

The boilers can, as an option, be operated with matching 

oil and gas burners to EN 267 and EN 676. 

These boilers are made from steel and are suitable for 

design temperatures of up to 120 °C (shutdown 

temperature of the high limit safety cut-out). 

1.2 Applications 

The Logano SK645 and SK745 low temperature boilers 

are suitable for all heating systems to DIN-EN 12828 and 

DIN-EN 12953-6. 

They are used for DHW and central heating in apartment 

blocks, municipal and commercial buildings, in district 

heating centres as well as for indirect heating of 

swimming pools. 

For DHW heating, these boilers can be combined with 

Buderus DHW cylinders. 

1.3 Characteristics and special features 

High standard seasonal efficiency [to DIN] and 

economic viability 

The large heating surface of the second pass and high 

grade thermal insulation result in excellent heat transfer as 

well as low flue gas and standby losses. The result is a 

standard seasonal efficiency [to DIN] of up to 93 %. 

Minimum circulation volumes are not required. 

Quiet operation with clean combustion 

The reversing combustion chamber with low combustion 

chamber volume loads ensures clean combustion and a 

high standard seasonal efficiency. 

Boiler supports that act to prevent structure-borne noise 

transfer and flue gas silencers result in significantly lower 

operating noise. 

Easy installation 

At the factory, these boilers are fitted with all required 

connections, enabling an easy integration into the heating 

system. Accessories are matched to these boilers, 

ensuring an easy and quick installation. For example, a 

safety assembly matched to these boilers safeguards 

uncomplicated installation. 

Predrilled burner plates make fitting third party burners 

easy. 

Straight-forward system design 

All boilers can be connected simply and in a straightforward 

manner to the heating system, since there is no 

special need for a minimum flow rate. Not only does this 

lead to reduced investment outlay and running costs, but 

also less engineering effort. 

Supplied fully wired ready for connection 

Easy connection to the heating system due to fully 

assembled delivery ex works. 

Easy maintenance and cleaning 

The combustion chamber and the heating surfaces of 

these boilers are easily accessible through the large door 

at the front that can be pivoted to the left or right. The 

smooth steel surfaces of these boilers can be easily 

cleaned with the cleaning set supplied as standard. 

Easy and convenient operation 

The control functions that are matched to the respective 

system hydraulics facilitate easy operation. These boilers 

can be combined with different Buderus control units. 

The equipment level of all control units can be extended 

individually with auxiliary modules. All control unit 

functions can be adjusted in only a few steps – through 

the push & turn – facility. 


2 Technical description 

2.1 Equipment level 

6 720 640 417-01.1il 

Fig. 1 Logano SK745 with Logamatic 4321 


are tested to EN 303, type-tested and CE-designated. 

Quality assurance measures to DIN-EN ISO 9001 

contribute to the high manufacturing quality and reliability 

of functions. The materials used in the Buderus low 

temperature boilers meet the requirements of EN 303 and 

EN 14394. As a result, these boilers operate safely and 

reliably. 

The boilers feature all-round thermal insulation and 

painted casing (RAL 5015). The thermal insulation is 

60 mm thick. The combustion chamber and the 

secondary heating surfaces are easily accessible through 

large front doors that can be pivoted to the left or right. 

Technical description 

Finely stepped output levels 

The Logano SK645 boilers are available with the 

following output ratings: 

• 120 kW 

• 190 kW 

• 250 kW 

• 300 kW 

• 360 kW 

• 420 kW 

• 500 kW 

• 600 kW 

The Logano SK745 boilers are available with the 

following output ratings: 

• 730 kW 

• 820 kW 

• 1040 kW 

• 1200 kW 

• 1400 kW 

• 1850 kW 

Available components 

• Logamatic 4212, 4321 and 4322 control units in a 

modular design 

• Drilled burner plate onto which the pressure-jet gas 

and oil burner are mounted 

• Plenty of matching accessories ( Chapter 10, 

page 52 ff.) 

6 720 646 816 (10/2010) – Technical guide Logano SK645 and SK745 5 

2

6 


2.2 Heating water routing 

Calculated flow and temperature processes 

A simulation program enabled the calculation of 

influencing factors, such as heat supply, amount of water, 

circulation etc. Subject to these factors, the flow and 

updraught characteristics as well as the temperature 

distribution within the boiler could be calculated and, step 

by step, optimised. The results of this simulation program 

were translated into the design of these low temperature 

boilers. 

2.3 Hot gas routing 

Inside the combustion chamber, the hot gases are 

reversed and flow towards the front of the boiler, where 

they are reversed again by the front door and guided into 

the second pass. They flow through the pipes, where they 

transfer their heat to the boiler water. 

AA 

Fig. 3 Hot gas flow inside the Logano SK645 and SK745 

AA Flue gas outlet 

RK Return 

VK Flow 

VSL Safety flow 

1 Combustion chamber 

2 Flue gas collector 

3 Pipes of the second pass 

1 

2 

VSL (VK 1) ) VK (VSL 1) ) 

Fig. 2 Heating water routing through the 

Logano SK645 and SK745 

RK Return 

VK Flow 


1 Pipes of the second pass 

2 Combustion chamber 

The design and geometry of the second pass ensure a 

high heat transfer rate from the hot gas to the boiler water. 

RK 

1) 

SK745 with 1400 kW and 1850 kW output 

RK 

VK 

VSL 

6 720 646 816 (10/2010) – Technical guide Logano SK645 and SK745 

3 

6 720 640 417-38.1il 

1 

2 

6 720 640 417-37.1il

2.4 Dimensions and specification 

2.4.1 Logano SK645 dimensions and specification 

Fig. 4 Dimensions, Logano SK645 120 kW to 600 kW 


Boiler size Unit 120 190 250 300 360 420 500 600 

Rated output kW 120 190 250 300 360 420 500 600 

Rated heat input kW 132 209 274 329 393 459 546 655 

Length L G mm 1345 1540 1670 1830 1803 2003 1933 2183 

Flue gas collector length L A mm 230 

Width B mm 780 840 870 870 940 940 1030 1030 

Height incl. control unit 

Height excl. control unit 

Width for transport 

Length for transport 

Boiler base frame 

Flue gas outlet 

B 

Combustion chamber 

length 


diameter 

Burner door depth 

Burner door height 

H 

H K 

L GR 

B GR 

D AA 

H AA 

L FR 1) 

D FR 1) 

L T 1) 

H B 

H 

H K 

H B 

mm 

mm 

mm 

mm 

mm 

mm 

mm 

mm 

mm 

mm 

mm 

mm 

A 1 A2 

1110 

880 

700 

1295 

915 

700 

200 

542 

865 

390 

195 

427 

1170 

940 

760 

1490 

1100 

760 

200 

582 

1060 

420 

195 

442 

Boiler flow 2) VK mm DN65 DN65 DN65 DN65 DN80 DN80 DN100 DN100 

Boiler return 2) RK mm DN65 DN65 DN65 DN65 DN80 DN80 DN100 DN100 

Flow safety pipe 2) VSL mm DN40 DN40 DN40 DN50 DN50 DN50 DN50 DN50 


1200 

970 

790 

1620 

1240 

790 

250 

597 

1190 

450 

1200 

970 

790 

1780 

1400 

790 

250 

597 

1350 

DEL Inches 

R1¼ 

Drain 

HEL mm 

200 

Tab. 1 Specification and dimensions Logano SK645 120 kW to 600 kW 

L G 

BGR LA LGR DEL A 3 

VSL VK RK 

195 

457 

450 

195 

457 

1270 

1040 

860 

1773 

1373 

860 

250 

632 

1260 

488 

195 

477 

H F 

H AA 

H EL 

1270 

1040 

860 

1973 

1573 

860 

250 

632 

1460 

488 

195 

477 

D AA 

6 720 640 417-02.1il 

1360 

1130 

950 

1913 

1503 

950 

300 

662 

1390 

548 

195 

507 

2 

1360 

1130 

950 

2163 

1753 

950 

300 

662 

1640 

548 

195 

507

8 


Boiler size Unit 120 190 250 300 360 420 500 600 

Flange height 

VK/VSL/RK 

Flange 

VK/VSL/RK 

H F mm 1005 1065 1095 1095 1165 1165 1255 1255 

A 1 

A 2 

A 3 

mm 

mm 

mm 

290 

170 

240 

320 

205 

345 

Transport weight kg 447 554 642 691 817 899 1063 1158 

Water content l 136 203 233 262 323 367 434 502 

Gas content l 129 183 238 268 304 350 420 495 

Flue gas temperature 3) 

Partial load 60 % 4) 

Full load 

Flue gas mass flow rate, 

oil 3) 

Partial load 60 % 

Full load 


gas 3) 


Full load 

CO 2 content, oil 

CO 2 content, gas 

Pressure drop on the 

hot gas side 

°C 

°C 

kg/s 

kg/s 

kg/s 

kg/s 

% 

% 

150 

210 

0.0316 

0.0527 

0.0314 

0.0523 

150 

205 

0.0494 

0.0824 

0.0488 

0.0813 

320 

185 

495 

150 

202 

0.0646 

0.1076 

0.0650 

0.1084 

480 

200 

470 

150 

200 

0.0769 

0.1282 

0.0778 

0.1297 

13 

10 

353 

225 

540 

150 

200 

0.0934 

0.1557 

0.0929 

0.1548 

553 

225 

540 

150 

200 

0.1085 

0.1809 

0.1068 

0.1780 

423 

365 

450 

150 

200 

0.1277 

0.2129 

0.1301 

0.2168 

673 

365 

450 

150 

200 

0.1538 

0.2564 

0.1556 

0.2593 

mbar 0.80 1.60 1.54 2.70 3.30 3.90 4.70 5.59 

Draught required Pa 0 

Maximum permissible 

temperature, high limit 

safety cut-out 5) 

Max. permiss. operating 

pressure (boiler) 

CE-designation, 

product ID 

°C 120 

bar 6 


CE 1015–07 

1) Fig. 15, page 15 

2) To DIN 2633 (PN 16) 

3) Relative to VL80/RL60 

4) To DIN-EN 303; the minimum flue gas temperature for the chimney calculation acc. to EN 13384-1 is approx. 12 K lower. 

5) Safety limit (high limit safety cut-out); maximum possible flow temperature = safety limit (high limit safety cut-out) - 18 K. 

Example: Safety limit (high limit safety cut-out) = 100 °C, maximum possible flow temperature = 100 - 18 = 82 °C 


2.4.2 Logano SK745 dimensions and specification 

B 

A 1 A2 



L G 


BGR LA LGR DEL B 

B GR 

H 

H K 

H B 

H 

HK H B 

L A 

A 1 


A 3 

VSL VK RK 

LG A2 A3 VK VSL 

RK 

L GR 

H F 

H AA 

H EL 

H F 

H AA 

H EL 

D AA 

6 720 640 417-02.1il 

D AA 

D EL 

2 

6 720 640 417-03.1il

10 


Boiler size Unit 730 820 1040 1200 1400 1850 

Rated output kW 730 820 1040 1200 1400 1850 

Rated heat input kW 795 893 1138 1313 1532 2024 

Length L G mm 2150 2350 2410 2710 2990 3410 

Flue gas collector length L A mm 215 215 215 215 330 330 

Max. length, incl. burner L B mm Burner-dependent 

Width B mm 1140 1140 1250 1250 1620 1700 

Height incl. control unit 

Height excl. control unit 

Width for transport 

Length for transport 

Boiler base frame 

Flue gas outlet 


length 


diameter 

Burner door depth 

Burner door height 

Boiler flow 2) 

Boiler return 2) 

Flow safety pipe 2) 

Drain 

Flange height 

VK/VSL/RK 

Flange 

VK/VSL/RK 

H 

H K 

L GR 

B GR 

D AA 

H AA 

L FR 1) 

D FR 1) 

L T 1) 

H B 

mm 

mm 

mm 

mm 

mm 

mm 

mm 

mm 

mm 

mm 

mm 

mm 

1470 

1240 

1060 

2130 

1700 

1060 

360 

727 

1585 

624 

195 

547 

1470 

1240 

1060 

2330 

1900 

1060 

360 

727 

1785 

624 

195 

547 

1580 

1350 

1170 

2390 

1960 

1170 

360 

797 

1845 

710 

195 

592 

VK mm DN125 DN125 DN125 DN125 DN150 DN200 

RK mm DN125 DN125 DN125 DN125 DN150 DN200 

VSL mm DN65 DN65 DN80 DN80 DN80 DN100 

D EL 

H EL 

Inches 

mm 

R1¼ 

200 

R1¼ 

200 

R1¼ 

200 

H F mm 1365 1365 1475 1475 1612 1732 

A 1 

A 2 

A 3 

mm 

mm 

mm 

448 

350 

620 

648 

350 

620 

Transport weight kg 1401 1504 1852 2024 2690 3540 

Water content l 607 675 822 942 1339 1655 


463 

595 

620 

1580 

1350 

1170 

2690 

2260 

1170 

360 

797 

2145 

710 

195 

592 

R1¼ 

200 

763 

595 

620 


– 

1481 

1320 

2990 

2316 

1320 

400 

1070 

2120 

780 

255 

635 

R1½ 

196 

260 

725 

725 

– 

1570 

1400 

3410 

2720 

1400 

400 

1145 

2520 

860 

285 

685 

R1½ 

206 

260 

725 

925


Boiler size Unit 730 820 1040 1200 1400 1850 

Gas content l 618 693 934 1071 1275 1710 

Flue gas temperature 3) 

Partial load 60 % 4) 

Full load 


oil 3) 


Full load 


gas 3) 


Full load 

CO 2 content, oil 

CO 2 content, gas 

Pressure drop on the 

hot gas side 

°C 

°C 

kg/s 

kg/s 

kg/s 

kg/s 

% 

% 

150 

198 

0.1868 

0.3113 

0.1869 

0.3116 

150 

198 

0.2088 

0.3480 

0.2102 

0.3503 


150 

198 

0.2651 

0.4418 

0.2671 

0.4451 

13 

10 

150 

195 

0.3049 

0.5082 

0.3089 

0.5148 

150 

195 

0.3571 

0.5952 

0.3600 

0.5999 

150 

195 

0.4725 

0.7875 

0.4761 

0.7935 

mbar 6.10 6.47 7.25 7.74 7.13 9.17 

Draught required Pa 0 

Maximum permissible 

temperature, high limit 

safety cut-out 5) 

Max. permiss. operating 

pressure (boiler) 

CE-designation, product 

ID 

°C 120 

bar 6 


CE 1015–07 

1) Fig. 15, page 15 

2) To DIN 2633 (PN 16) 

3) Relative to VL80/RL60 

4) To DIN-EN 303; the minimum flue gas temperature for the chimney calculation acc. to EN 13384-1 is approx. 12 K lower. 

5) Safety limit (high limit safety cut-out); maximum possible flow temperature = safety limit (high limit safety cut-out) - 18 K. 

Example: Safety limit (high limit safety cut-out) = 100 °C, maximum possible flow temperature = 100 - 18 = 82 °C 

2

12 


2.5 Parameters 

2.5.1 Pressure drop on the water side 

The pressure drop on the water side is the pressure 

differential between the boiler flow and return 

connections. It depends on the VK/RK connector size 

and the heating water flow rate. 

ΔpH (mbar) 

100 

10 

1 

1 

Fig. 7 Pressure drop on the water side Logano SK645 

ΔpH Pressure drop 

VH Heating water flow rate 

1 SK645: 120 kW 

2 SK645: 190 kW, 250 kW, 300 kW 

3 SK645: 360 kW, 420 kW 

4 SK645: 500 kW, 600 kW 

Calculation example for SK645 250 kW: 

Given 

• ΔT = 15 K 

• c = 4.19 kJ/kg × K 

• DensityWater = approx. 1000 kg/m 3 

ΔP H calculated as follows: 

Q = m × c × ΔT 

m 

m 

Q 

= --------------c 

× ΔT 

Result 

• m = 14320 kg/h 

V H 

1 2 3 4 

Result 

• The intersection of the straight line 2 and V H = 

14.3 m 3 /h results in ΔP H = 30 mbar 

10 

250 kW 

= ------------------------------------------------- × 3600 s/h 

4,19 kJ/kg K × 15 K 

14320 kg/h 

1000 kg/m 3 

------------------------------ 14,3 m 3 = = /h 

100 

VH (m3 /h) 

6 720 640 417-04.1il 

ΔpH (mbar) 

100 

10 

1 

10 

1 2 3 

Fig. 8 Pressure drop on the water side Logano SK745 

ΔpH Pressure drop 

VH Heating water flow rate 

1 SK745: 730 kW, 820 kW, 1040 kW, 1200 kW 



1000 

VH (m3 /h) 


100 

6 720 640 417-05.1il

2.5.2 Boiler efficiency 

The boiler efficiency h K identifies the ratio between the 

rated output and the rated heat input. It is shown subject 

to the average boiler water temperature and the boiler 

output. 

Hi (%) 

96 

95 

94 

93 

92 

91 

1 

2 

90 

50 60 70 80 

ϑK (°C) 

Fig. 9 Boiler efficiency subject to the average boiler 

water temperature (average value for the 

complete model range) - Logano SK645 

Hi Efficiency, net calorific value 

ϑK Average boiler temperature 

1 Boiler efficiency at stage 1 (partial load 60 %) 

2 Boiler efficiency at stage 2 (full load 100 %) 

Calculation example for average boiler water temperature: 

ϑK Average boiler water temperature 

TRK Return temperature 

TVK Flow temperature 

Hi (%) 

96 

95 

94 

93 

92 

91 

1 

2 

ϑ K 

TVK – TRK = ------------------------ 

2 

Fig. 10 Boiler efficiency subject to the average boiler 

water temperature (average value for the 

complete model range) - Logano SK745 



1 Boiler efficiency at stage 1 (partial load 60 %) 

2 Boiler efficiency at stage 2 (full load 100 %) 

6 720 640 417-06.1il 

90 

50 60 70 80 

ϑK (°C) 

6 720 640 417-08.1il 


Fig. 11 Boiler efficiency and flue gas temperature 

subject to the boiler load at an average boiler 

water temperature of 70 °C - Logano SK645 


Q/Qmax Relative boiler load 

ϑA Flue gas temperature 

1 Boiler efficiency 

2 Flue gas temperature 

Fig. 12 Boiler efficiency and flue gas temperature 

subject to the boiler load at an average boiler 

water temperature of 70 °C - Logano SK745 


Q/Qmax Relative boiler load 


1 Boiler efficiency 

2 Flue gas temperature 


H i (%) 

98 

96 

94 

92 

90 

2 

1 

ϑ A (°C) 

200 

180 

160 

140 

120 

0 10 20 30 40 50 60 70 80 90 

100 

100 

Q/Qmax (%) 

H i (%) 

98 

96 

94 

92 

90 

1 

2 

6 720 640 417-07.1il 

ϑ A (°C) 

200 

180 

160 

140 

120 

0 10 20 30 40 50 60 70 80 90 

100 

100 

Q/Qmax (%) 

6 720 640 417-33.1il 

2

14 


2.5.3 Standby loss and flue gas temperature 

The standby loss is part of the rated heat input that is 

required to achieve the specified boiler water 

temperature. The cause of this loss is the cooling down of 

the boiler through radiation and convection during the 

standby time (burner idle time). 

qB (%) 

0,4 

0,3 

0,2 

0,1 

Radiation and convection result in part of the output being 

transferred continuously from the boiler surface to the 

ambient air. In addition to this surface loss, the boiler can 

also cool down to a lesser degree through the chimney 

draught. The flue gas temperature depends on the 

average boiler water temperature and the boiler load. 

Fig. 13 Standby loss and flue gas temperature, subject to the average boiler water temperature - Logano SK645 

qB Standby loss 



1 Flue gas temperature (full load 100 %) 

2 Standby loss 

3 Flue gas temperature (partial load 60 %) 

Fig. 14 Standby loss and flue gas temperature, subject to the average boiler water temperature - Logano SK745 

qB Standby loss 



1 Flue gas temperature (full load 100 %) 

2 Standby loss 

3 Flue gas temperature (partial load 60 %) 

1 

3 

2 

ϑ A (°C) 

0 

100 

50 60 70 80 

ϑK (°C) 


200 

180 

160 

140 

120 

6 720 640 417-09.1il 

q B (%) ϑ A (°C) 

0,2 

0,1 

1 

2 

3 

0 

50 60 70 

100 

80 

ϑK (°C) 

200 

180 

160 

140 

120 

6 720 640 417-45.1il

3 Burner 

3.1 Burner selection 

Either pressure-jet oil or gas burners can be used with the 

Logano SK645 and SK745 low temperature boilers. The 

pressure-jet oil burners must be approved to EN 267, and 

the pressure-jet gas burners to EN 676. 2-stage or 

modulating burners can be used. 

When selecting a burner take into account that the 

pressure drop on the hot gas side must be overcome 

reliably. When positive pressure at the flue outlet is 

required (sizing of the flue system), take this into 

consideration in addition to the pressure drop on the hot 

gas side. 

3.2 Burner requirements 

Observe the installation instructions issued by the burner 

manufacturer where the burner installation is concerned. 

T 

1) 

D MB 

L FR 

Fig. 15 Burner installation dimensions 

D FR 

6 720 640 417-10.1il 

DFR Combustion chamber diameter 

(dimensions page 7 and page 10) 

DMB Maximum diameter 

LFR Combustion chamber length 

(dimensions page 7 and page 10) 

T Burner door depth (dimensions page 7 and 

page 10) 

1) The blast tube must protrude beyond the lining in the 

burner door. 

Burner 

To make engineering and installation easier, burners and 

drilled burner plates are available as accessories for the 

Logano SK645 and SK745 boilers. The boilers are 

supplied with a dummy plate. 

For further details regarding these burners 

and associated burner plates, see the current 

Buderus heating equipment catalogue. The 

selection of a suitable burner for the specific 

project can be discussed in detail with the 

Buderus sales office. 

Logano Boiler 

size 

SK645 


Max. diameter 

D MB 

[kW] [mm] 

120 130 

190 240 

250 240 

300 240 

360 290 

420 290 

500 290 

600 290 

730 350 

820 350 

1040 350 

1200 350 

1400 350 

1850 350 

Tab. 3 Burner dimensions for Logano SK645 and 



3

16 

4 Regulations and operating conditions 


4.1 Extracts from the regulations 


comply with the requirements to EN 303 and EN 14394, 

and they are approved in line with the Pressure 

Equipment Directive up to ≤ 120 °C. They are suitable for 

heating systems in line with the requirements to 

DIN-EN 12828 and the additional requirements to 

DIN-EN 12953-6. 

Observe the following regarding creation and operation of 

the system: 

• Standard building regulations 

• Statutory regulations 

• Country-specific regulations 

Installation, oil and gas connection, flue gas connection, 

commissioning, power supply, maintenance and repair 

work must only be carried out by authorised contractors. 

Permits 

The local gas supply utility may need to be notified of and 

approve the installation of a low temperature boiler with 

gas burner. We recommend clarifying the match between 

boiler and flue system with the relevant bodies at the 

planning stage. Where required, inform your local flue gas 

inspector prior to commissioning. It may be necessary to 

obtain a permit for the flue system at regional level. 

Annual inspection and demand-dependent 

maintenance 

To ensure the reliability of functions and the energetic 

quality, the HEVAC sector recommends at least an annual 

inspection. If any condition requiring maintenance work is 

identified in the course of an inspection, that maintenance 

work must be carried out as required. We recommend to 

system users to enter into a maintenance and inspection 

contract with a heating contractor or the burner 

manufacturer. 

4.2 Pressure Equipment Directive (PED) and Health & Safety at Work Act 

4.2.1 Application range 

The Pressure Equipment Directive applies to safety 

temperatures > 110 °C; i.e. a boiler equipped with a high 

limit safety cut-out 110 °C is excluded from the provision 

of the Pressure Equipment Directive and from the Health 

& Safety at Work Act [Germany] where the requirements 

for products that must be supervised is concerned. 

4.2.2 Categories in accordance with the Pressure Equipment Directive 97/23/EC 

The Pressure Equipment Directive identifies four 

categories, split according to the respective 

pressure:volume product, into which boilers fall. 

Logano Boiler size Category I Category II Category III Category IV 


+ Applicable 

– N/A 

[kW] 

p×V≤ 50 p×V≤ 200 p×V≤ 1000 p×V>1000 V > 1000 or p × V > 3000 

120 – – + – – 

190–500 – – – + – 

600 – – – – + 

SK745 730–1850 – – – – + 

Tab. 4 Categories in accordance with the Pressure Equipment Directive 97/23/EC 


4.2.3 Health & Safety at Work Act regarding steam and hot water boilers 

The Health & Safety at Work Act [Germany] enacted on 

the 3 October 2002 and applicable to hot water and 

steam boiler systems as of 1 January 2003 specifies 

demanding requirements, particularly for boilers in 

category III and category IV. 

Proviso with regard to granting permission 

(para. 13 BetrSichV) [Germany] 

Assembly, installation and the operation of boilers in 

category IV require permission from the relevant authority 

[Germany]. 

Inspection prior to commissioning 

(para. 14 BetrSichV) 

Boilers category I and II can be checked in situ, i.e. as part 

of the system, by an authorised person (master heating 

system builder). 

4.2.4 Overview of the Health & Safety at Work Act [Germany] 

+ Required 

– Not required 

Proviso with regard 

to granting 

permission 

Regulations and operating conditions 

Boilers in categories III and IV must be checked by an 

authorised supervisory body in situ, prior to 

commissioning. 

Repeated inspections (para. 15 BetrSichV) 

Boilers in category III with a pressure:volume product 

p × V greater than 1000 and boilers in category IV must 

be checked regularly by an authorised supervisory body in 

situ: 

• External inspection no later than after 12 months 

• Internal inspection no later than after three years 

• Strength test no later than after nine years 

The test intervals must be determined by the system user 

based on a safety-technical assessment, the result of 

which must be checked by an authorised supervisory 

body. 

Inspection 

prior to 

commissioning 

Repeated 

inspections 

§13 §14 §15 

Boiler category I (up to 50 bar × l) – + 1) 

– 1) 

Boiler category II (up to 200 bar × l) – + 1) 

Boiler category III (up to 1000 bar × l) – + – 1) 

Boiler category III (> 1000 bar × l) – + + 

Boiler category IV (> 3000 bar × l) + + + 

Tab. 5 Overview of the Health & Safety at Work Act [Germany] 

1) May be carried out by an authorised person (e.g. master heating system builder) 


– 1) 

4

18 


4.3 Operating conditions 

4.3.1 Operating requirements 

The operating conditions in Tab. 6 are part of the warranty 

conditions for the Logano SK645 and SK745 low 

temperature boilers. These operating conditions are 

4.3.2 Operating conditions 

Logano Minimum 

flow rate 





No requirements 1) 

No requirements 1) 

Boiler operating conditions 

assured through a suitable hydraulic circuit and boiler 

control (hydraulic connection page 26). 

Minimum return temperature in °C With operating 

interruptions 

With oil combustion With gas combustion 

Two-stage 

burner 

Modulating 

burner 

Two-stage 

burner 

Modulating 

burner 

In conjunction with a Logamatic control unit for modulating low temperature operation 

50 50 60 60 

In conjunction with a Logamatic control unit for constant boiler water temperatures, 

e.g. Logamatic 4212 with ZM427, or with auxiliary external control unit 

Tab. 6 Operating conditions for Logano SK645 and SK745 

1) Ensure that the return temperature sensor FV/FZ is always surrounded by water. 

No requirement 

The boiler is shut down 

automatically by the 

Logamatic control unit 

50 50 60 60 No requirements 


4.4 Fuel 

Operation with fuel oil 


can be operated with fuel oil EL to DIN 51603. 

All boilers can also be used without restriction with 

rapeseed oil. Pressure-jet burners for rapeseed oil can be 

obtained from burner manufacturers on request. 

Operation with gas 

All low temperature boilers are suitable for natural gas E 

or LL as well as LPG. Observe the burner manufacturer's 

details. 

The gas quality must comply with the requirements of the 

DVGW Code of Practice G 260 [Germany]. 

To be able to adjust the gas throughput, install a gas 

meter that can be checked, even in the lower load range 

of the burner. This also applies to LPG systems. 

Biogas (e.g. gas from waste disposal or sewerage works) 

can also be used. For this, observe special operating 

conditions. Pressure-jet burners for biogas are available 

from burner manufacturers on request. 

Additional operating conditions for the operation 

with biogas 

The following operating conditions must be met: 

• Operate boiler at constant temperature 

• Never permit operating interruptions 

• Maintain a minimum return temperature above the dew 

point (in this case at least 68 °C), i.e. return 

temperature raising measures 

• Ensure minimum boiler water temperature of 83 °C 

• Clean and maintain the boiler regularly, possibly clean 

chemically and then preserve 

• Combustion of biogas/waste gas (quality in line with 

DVGW G262, Tab. 3): 

– Proportion of sulphur and sulphur compounds in the 

gas up to a maximum of 1500 mg/m 3 (approx. 0.1 % 

by vol.) 

– Proportion of chlorine and chlorine compounds in 

the gas up to a maximum of 50 mg/m 3 

– Proportion of fluoride and fluoride compounds in the 

gas up to a maximum of 25 mg/m 3 

In view of the high degree of corrosiveness, and in 

variance from Fig. 8.5 of our general sales, delivery and 

payment terms, the warranty period is limited to 2 years. 


4.5 Water treatment 

As pure water cannot be used for heat transfer, water 

quality is important. Poor water quality can lead to 

limescale formation and corrosion. Consequently, 

particular attention must be paid to water quality, water 

treatment and, above all, continuous water monitoring. 

Water treatment is an essential factor in ensuring troublefree 

operation, availability, a long service life and the 

efficiency of the heating system. 

4.5.1 Definition of terms 

Limescale formation is the formation of hard deposits 

on walls inside hot water heating systems. These deposits 

are made up of substances contained in the water, 

essentially calcium carbonate. 

Heating water is any water used for heating purposes in 

a hot water heating system. 

Fill water is the water used to completely fill the heating 

system on the heating water side for the first time and with 

which it is then heated up. 

Top-up water is any water used to top up the system on 

the heating water side after the first time it is heated up. 

Operating temperature is the temperature captured at 

the flow connector of the heating appliance in a hot water 

heating system when operating correctly. 

Water volume Vmax is the maximum volume of 

untreated fill and top-up water in m 3 that may be 

introduced into the system over the entire service life of 

the boiler. 

Corrosion-inhibiting sealed unvented systems are 

heating systems in which no significant amount of oxygen 

ingress into the heating water is possible. 

4.5.2 Prevention of corrosion damage 

In most cases, corrosion plays only a minor role in heating 

systems. That is based on the fundamental requirement 

that the system is a corrosion-inhibiting sealed unvented 

system, i.e. one that prevents a continuous ingress of 

oxygen. 

Continuous ingress of oxygen leads to corrosion and can 

thus cause rusting and the formation of rust sludge. 

Sludge formation can not only cause blockages and 

therefore a diminished heat supply but also deposits 

(similar to limescale deposits) on the hot surfaces of heat 

exchangers. 

The most important factor with regard to ingress of 

oxygen is generally pressure maintenance and, in 

particular, the function, correct sizing and adjustment 

(pre-charge pressure) of the expansion vessel. Check the 

function and pre-charge pressure annually. If continuous 

ingress of oxygen cannot be prevented (e.g. due to plastic 

pipes that are permeable to oxygen) or if the system 

cannot be designed as a sealed unvented system, anticorrosion 

measures such as the addition of approved 


4

20 


chemical additives or system separation by means of a 

heat exchanger are necessary. 

Oxygen binding agents can be used, for example, to bind 

the oxygen. 

The pH value of untreated heating water should be 

between 8.2. and 9.5. Ensure that the pH level changes 

after commissioning, especially due to the separation of 

oxygen and limescale. It is recommended to check the pH 

level after several months of heating system operation. 

The water can be alkalised by the addition of trisodium 

phosphate, if necessary. 

If additives or antifreeze (where approved by 

Buderus) are used in the heating system, 

check the heating water regularly in 

accordance with the manufacturer's 

instructions. Carry out all necessary 

corrections ( Chapter 4.5.8, page 23). 

4.5.3 Prevention of damage through scale 

formation 

VDI 2035-1 “Prevention of damage to hot water central 

heating systems through limescale formation”, issue 12/ 

2005 applies to DHW heating systems to DIN 4753 and 

hot water central heating systems to DIN 12828 with a 

design operating temperature of up to 100 °C. 

One of the aims of the current edition of VDI 2035-1 is 

simplification of its application. For that reason, standard 

values for the amount of limescale-forming substances 

(total alkaline earths) for specified heat output ranges are 

recommended. The specifications are based on practical 

Total boiler output 

[kW] 

Q ≤ 50 V max : no requirements 

experience that shows that damage due to limescale 

formation is dependent on the total heat output, the 

system volume, the cumulative volume of fill and top-up 

water used over the service life of the system and the 

boiler design. 

The details given below in respect of Buderus boilers are 

based on many years of experience and service life tests, 

and specify the maximum cumulative amount of fill and 

top-up water subject to output, water hardness and boiler 

material. This ensures compliance with the aims of 

VDI 2035-1 “Prevention of damage through limescale 

formation in hot water heating systems”. 

Warranty claims in respect of Buderus boilers are only 

valid in conjunction with the requirements specified herein 

and a fully completed system log. 

4.5.4 Requirements for fill and top-up water 

To protect boilers against limescale damage over their 

entire service life and to ensure trouble-free operation, the 

total amount of limescale-forming substances in the fill 

and top-up water in heating systems must be restricted. 

Therefore, the fill and top-up water has to meet certain 

requirements that are dependent on the total boiler output 

and the resulting total volume of water in the heating 

system ( Tab. 7). 

The permissible amount of water based on the fill water 

quality can be determined simply with the aid of the 

diagrams in Fig. 16 and Fig. 17 or a calculation method to 

determine the permissible amounts of fill and top-up water 

( page 23). 

Requirements regarding water hardness and the amount of fill and top-up 

water V max 

50 ≤ Q ≤ 600 V max: calculate according to diagrams in Fig. 16 and Fig. 17 as well as formula 1 

Q > 600 Water treatment is generally required 

independent of output For systems with very large water content (> 50 l/kW), water should generally be treated 

Tab. 7 Requirements for fill and top-up water for boilers made from ferrous material 


4.5.5 Application limits for boilers made from ferrous materials 

V max (m 3 ) 

12 

10 

8 

6 

4 

2 

Fig. 16 Boilers ≥ 50 kW to 150 kW made from ferrous materials 

HW Water hardness 

V max Maximum fill and top-up water over the entire service life 

of the boiler 

1 Boilers up to 150 kW 



Example 

Given: 

• Boiler output Q =105 kW 

• System volume VA = approx. 1.1 m 3 

Result: 

• At a water hardness level of 22 °dH, the maximum 

amount of fill and top-up water is approx. 1.8 m 3 . 

• This system can be filled with untreated tap water. 


0 

0 5 10 15 20 25 30 

HW (°dH) 

6 720 640 417-35.1il 

1 

2 

3 

Measures are required above these output 

curves; fill with untreated tap water below the 

curves. In multi-boiler systems (< 600 kW 

total boiler output) the output curves for the 

smallest single boiler apply. 

One suitable measure for boilers made from 

ferrous material is, for example, total 

softening ( current Buderus catalogue, 

technical customer service, provision of 

mobile water treatment systems). 


4

22 


V max (m 3 ) 

45 

40 

35 

30 

25 

20 

15 

10 

5 

0 

0 5 10 15 20 25 30 

6 720 640 417-36.1il 

Fig. 17 Boilers > 150 kW to 600 kW made from ferrous materials 

HW Water hardness 

V max Maximum fill and top-up water over the entire service life 

of the boiler 







Example 

Given: 

• Boiler output Q =295 kW 

• System volume VA = approx. 7.5 m 3 

Result: 

• At a water hardness level of 18 °dH, the maximum 

amount of fill and top-up water is approx. 6.0 m 3 . 

• The amount of fill water is already greater than the 

permissible amount of fill and top-up water. Fill the 

system with treated water. 

1 

2 

3 

4 

5 

6 

Measures are required above these output 

curves; fill with untreated tap water below the 

curves. In multi-boiler systems (< 600 kW 

total boiler output) the output curves for the 

smallest single boiler apply. 

H W (°dH) 

One suitable measure for boilers made from 

ferrous material is, for example, total 

softening ( current Buderus catalogue, 

technical customer service, provision of 

mobile water treatment systems). 


4.5.6 Recording the amounts of fill and top-up 

water 

For heating systems > 50 kW, VDI 2035-1 specifies the 

fitting of a water meter and the keeping of a system log. 

You will find the log with the technical documents 

supplied with Buderus boilers. Warranty claims in respect 

of Buderus boilers are only valid in conjunction with the 

requirements specified herein and a fully completed log. 

4.5.7 Calculation to determine the permissible 

amounts of fill and top-up water 

The fill and top-up water has to meet certain requirements 

depending on the total boiler output and the resulting 

water volume of a heating system. 

Use the following formula to calculate the maximum 

amount of fill water for heating systems ≤ 600 kW that 

may be introduced without treatment: 

Form. 1 Calculation of the maximum amount of water 

that may be introduced without treatment 

Ca(HCO3)2 Calcium hydrogen carbonate concentration 

in mol/m 3 

Q Boiler output in kW (in case of multi-boiler 

V max 

V max 

systems the output of the smallest boiler) 

Maximum volume of untreated fill and top-up 

water in m 3 that may be introduced over the entire 

service life of the boiler 

Example 

Calculation of the maximum permissible amount of fill and 

top-up water Vmax for a heating system with a total boiler 

output of 420 kW. The analysis values for carbonate 

hardness and calcium hardness are quoted in the older 

unit °dH. 

Carbonate hardness: 15.7 °dH 

Calcium hardness: 11.9 °dH 

From the carbonate hardness, we obtain: 

Ca (HCO3 ) 2 = 15.7 °dH × 0.179 = 2.8 mol/m3 From the calcium hardness, we obtain: 

Ca (HCO3 ) 2 = 11.9 °dH × 0.179 = 2.13 mol/m3 The lower of the two values calculated from the calcium 

and carbonate hardness is the definitive figure for 

calculating the maximum permissible water volume Vmax. V max 

Q 

= 0,0626 × ------------------------------- 

Ca( HCO3) 2 

420 kW 

0,0626 

2,13 mol/m 3 

× ------------------------------- 12,3 m 3 

= = 


4.5.8 Chemical heating water additives 

If plastic pipes that are permeable to oxygen are used in 

underfloor heating systems, the corrosion process can be 

prevented by adding chemicals into the heating water. In 

such cases, ask the manufacturer of these chemical 

additives for a certificate verifying the compatibility with 

different parts of the system and the materials used in the 

heating system. 

Chemical additives for which no such 

certificate of compatibility can be issued by 

the manufacturer must not be used. 

Use of antifreeze 

For decades now, antifreeze based on glycol has been 

used in heating systems. For example, Antifrogen N made 

by Clariant (sold via the Buderus wholesale network). 

The use of alternatives is acceptable, subject to such 

products being the equivalent of Antifrogen N. 

Observe the information supplied by the antifreeze 

manufacturer. Follow the manufacturer's details regarding 

mixing ratios. 

The specific thermal capacity of Antifrogen N antifreeze is 

lower than the specific thermal capacity of water. To 

enable the transfer of the required heat output, increase 

the required flow rate accordingly. This should be taken 

into account when sizing system components (e.g. 

pumps) and the pipework. In addition, a higher flue gas 

temperature results, lowering the boiler efficiency. 

As the heat transfer medium has a higher viscosity and 

density than water, take the higher pressure drop through 

the pipework and other system components into account. 

The resistance of all plastic components in the system 

must be checked separately. 

4.5.9 Combustion air 

Where combustion air is concerned, ensure that it is not 

heavily contaminated with dust and contains no 

halogenated compounds. Otherwise there would be a risk 

of damage to the combustion chamber and the secondary 

heating surfaces. 

Halogenated compounds are highly corrosive. These are 

contained, for example, in spray cans, thinners, cleaning & 

degreasing agents and in solvents. 

Design the combustion air supply so that, for example, no 

extract air is drawn in from chemical cleaners or paint 

shops. Special requirements apply to the supply of 

combustion air in the installation room ( page 49). 


4

24 

5 Heating controls 

5 Heating controls 

5.1 Logamatic 4000 control system 

A control unit is required to operate boilers. The Buderus- 

Logamatic control systems are of modular design. This 

enables the system to be matched affordably to the 

individual applications and equipment installed in the 

intended heating system. 

Subject to requirements and the heating system layout, 

the following are available for selection as the boiler 

control system: 

• Logamatic 4212 control unit (ZM427 for boiler 

operating conditions) 

• Logamatic 4321 and 4322 control units 

• Logamatic 4411 control panel system 

The power contactors of the burner switched by the 

control unit may require a burner control panel. As an 

alternative, the power contactors may also be integrated 

into the Buderus control panel system. 

The technical guide “Modular Logamatic 

4000 control system” contains more detailed 

information on the Logamatic 4212, 4321 

and 4322 control units. 

5.1.1 Logamatic 4212 control unit 

The conventional Logamatic 4212 control unit is suitable 

for operation with a constant boiler water temperature. 

Where a higher-ranking control is used, e.g. a 

Logamatic 4411 (DDC systems and building 

management systems), the Logamatic 4212 transfers 

the burner switching commands to the burner. 

The standard equipment contains the safety equipment 

for a 2-stage burner operation. Boiler circuit actuators and 

boiler circuit pumps can be switched with the ZM427 

auxiliary module, thereby safeguarding the boiler 

operating conditions. Furthermore, the ZM427 module 

facilitates an enabling of the burner stages with a higherranking 

control using floating contacts. 

5.1.2 Logamatic 4321 and Logamatic 4322 

control units 

The Logamatic 4321 control unit enables the low 

temperature operation of these boilers and provides the 

operating conditions in conjunction with the 2-stage or 

modulating burner in a single boiler system. 

Up to eight heating circuits with actuator can be 

controlled with corresponding function modules. The 

range of functions also includes the complete boiler 

circuit control with optional switching of a boiler circuit 

actuator and one boiler circuit pump. 

2 and 3-boiler systems require a Logamatic 4321 control 

unit that functions as “Master” for the first boiler and one 

Logamatic 4322 control unit each as lag appliance for the 

second and third boiler. The combination of devices with 

corresponding function modules can control up to 22 

heating circuits with actuator. 

5.1.3 Logamatic 4411 control panel system 

The Logamatic 4411 control panel system from Buderus 

is the comprehensive solution, representing advanced 

control technology for complex heating systems that 

require a system-specific control. 

The local sales office assists with the engineering and 

supplies optimum system solutions for each individual 

case. This also applies to programmable logic controls 

(DDC systems) and building management systems. 

5.2 Logamatic telecontrol system 

The Logamatic telecontrol system is the ideal addition to 

all Buderus control systems. It comprises several 

software and hardware components and enables heating 

contractors to provide even better customer support and 

services via a powerful remote control facility. It can be 

used in rental apartment buildings, holiday homes as well 

as in medium and large heating systems. The Logamatic 

telecontrol system is suitable for remote monitoring, 

parameter setting and fault diagnosis in heating systems. 

It offers ideal conditions for heat supply concepts and 

maintenance and inspection contracts. 

The technical guide “Logamatic Telecontrol 

system” contains more detailed information. 


6 DHW heating 

6.1 Systems for DHW heating 


can also be used to provide DHW heating. The Buderus 

Logalux DHW cylinders that are matched to the boiler 

output can be used. These are available as vertical and 

horizontal versions in different sizes with 150 l to 6000 l 

capacity. Subject to application, they are equipped with 

an internal indirect coil or an external heat exchanger 

( Fig. 18 and Fig. 19). 

Fig. 18 DHW heating according the cylinder principle 

with internal indirect coils 

VH 

RH 

VS 

RS 

Fig. 19 DHW heating according to the primary store 

principle with external heat exchangers 

Key to Fig. 18 and Fig. 19: 

AW DHW outlet 

EK Cold water inlet 

RH Fuel return (to the boiler) 

RS Cylinder return 

VH Fuel flow (from the boiler) 

VS Cylinder flow 

AW 

The cylinders can be used singly or in combination with 

other cylinders. With the primary store system, different 

cylinder sizes and different heat exchanger sets can be 

combined. System solutions are therefore available for 

any demand and many applications. 

EK 

6 720 640 417-11.1il 

AW 

EK 

6 720 640 417-12.1il 

DHW heating 

6.2 DHW temperature controller 

The DHW temperature is set and regulated either by 

means of a module inside the boiler control unit or via a 

separate control unit dedicated to DHW heating. The 

control units for DHW heating are specifically matched to 

the heating control unit and offer many application 

options. For more detailed information in this connection, 

see the technical guides “Sizing and selecting DHW 

cylinders” and “Modular control system Logamatic 4000”. 


6

26 

7 System examples 


7.1 Information regarding all system examples 

The examples in this section show options for 

hydraulically connecting the Logano SK645 and SK745 

low temperature boilers without safety criteria. 

For detailed information regarding the number, equipment 

level and control of the heating circuits as well as on the 

installation of DHW cylinders and other consumers, see 

the respective technical guides. 

The DHW heating systems shown can be implemented as 

DHW cylinder or primary store system. 

This particular system example does not represent a 

binding recommendation for implementing a specific 

heating network. The practical implementation is subject 

to currently applicable technical rules. 

Information regarding further options for system layout 

and engineering aids are available from the staff in 

Buderus sales offices. 

7.1.1 Hydraulic connection 

Steps for controlling the return and boiler water 

temperature 

The Buderus Logamatic 4321, 4322 and 4212 control 

units with the ZM427 auxiliary module, together with the 

corresponding boiler or heating circuit actuators, ensure 

the required minimum return temperature. 

Alternatively, the Logamatic 4321 and 4322 control units 

enable operation with minimum boiler water temperature. 

Allow for the temperature sensors required 

for raising the return temperature as 

immersion sensors. 

For demand-dependent system suggestions with 

explanations of the respective functions and application 

limits, see page 30 to page 46. 

Heating circuit pumps 

Size pumps in central heating systems in accordance with 

current technical rules. 

Dirt traps 

Deposits in heating systems can lead to local overheating, 

noise and corrosion. Any resulting boiler damage falls 

outside the warranty obligations. 

To remove dirt and sludge deposits, flush the heating 

system thoroughly prior to installing and commissioning a 

boiler in an existing system. In addition, we recommend 

the installation of dirt traps or a blow-down facility. 

Dirt traps retain contaminants and thereby prevent 

operating faults in control devices, pipework and boilers. 

Fit these near the lowest point of the heating system in an 

easily accessible position. Clean the dirt traps every time 

the heating system is serviced. 

Position of strategy flow temperature sensor 

In multi-boiler systems with strategy flow temperature 

sensor (FVS), the sensor should be located as close to 

the boiler system as possible. This rule does not apply if a 

low loss header is used to provide hydraulic balance. 

Additional time lag due to long distances between the 

boiler system and the strategy flow temperature sensor 

has a negative effect on the control characteristics, 

especially in the case of boilers with modulating-control 

burners. 


7.1.2 Control 

Operating temperatures should be controlled with the 

Logamatic control unit taking account of the outside 

temperature. The room temperature dependent control of 

individual heating circuits (with room temperature sensor 

in a reference room) is an option. For this, actuators and 

heating circuit pumps are switched constantly by the 

Logamatic control unit. Number and version of the 

controllable heating circuits are dependent on the 

selection and equipment level of the control unit. The 

Logamatic control unit also switches the burner, 

independently of whether these are 2-stage or modulating 

pressure-jet burners. Different burner types can be 

combined in multi-boiler systems. 3-phase burner and 

3-phase pumps must be electrically connected on site. 

These are switched by the Logamatic control unit (230 V). 

The technical documents of the control units 

include detailed information. 

7.2 Safety equipment to DIN-EN 12828 and DIN-EN 12953-6 

7.2.1 Requirements 

The diagrams and corresponding technical information in 

connection with system examples do not cover all 

available options. Each system example does not 

represent a binding recommendation for a specific 

heating network implementation. The practical 

implementation is subject to currently applicable technical 

rules. Safety equipment shall be installed in accordance 

with local regulations. 

DIN-EN 12828 specifies the safety equipment for safety 

temperatures up to 110 °C. For safety temperatures in 

excess of 110 °C refer to DIN-EN 12953-6. 

Furthermore, consider the additional requirements 

regarding the system operation as specified in the Health 

& Safety at Work Act. The schematic diagrams in Fig. 20 

to Fig. 23 can be used as engineering aids. 

System examples 

7.1.3 DHW heating 

Given an appropriate design, the DHW temperature 

control by means of a Logamatic control unit offers 

special functions, such as the switching of a DHW 

circulation pump or thermal disinfection to protect against 

the growth of legionella bacteria, for example. 

In this connection, the technical guide 

“Sizing and selecting DHW cylinders” 

provides detailed information. 


7

28 


7.2.2 Arrangement of safety equipment to DIN-EN 12828; operating temperature ≤ 105 °C; 

shutdown temperature (high limit safety cut-out) ≤ 110 °C 

Boiler ≤ 300 kW; operating temperature ≤ 105 °C; 

shutdown temperature (high limit safety cut-out) 

≤ 110 °C – direct heating 

6/7 

11 

3 1) 

12 13 

1 

2 

4 1) 

≤ 300 kW 

Fig. 20 Safety equipment to DIN-EN 12828 for boilers 

≤ 300 kW with high limit safety cut-out ≤ 110 °C 

The figures show the safety equipment to DIN-EN 12828 

schematically for the system version – although other 

options are available. The practical implementation is 

subject to currently applicable technical rules. 

5 1) 

15 

14 15 

2 13 

10 

16 

13 

17 

VK 

RK 

6 720 640 417-13.1il 

Boiler > 300 kW; operating temperature ≤ 105 °C; 

shutdown temperature (high limit safety cut-out) 

≤ 110 °C – direct heating 

8 

0,5 % 

6/7 

11 

3 1) 

12 13 

Fig. 21 Safety equipment to DIN-EN 12828 for boilers 

> 300 kW with high limit safety cut-out 

≤ 110 °C 


RK Return 

VK Flow 

1 Heat source 

2 Shut-off valve, flow/return 

3 Temperature controller (TR) 

4 High limit safety cut-out (STB) 

5 Temperature measuring facility 

6 Diaphragm safety valve MSV 2.5 bar/3.0 bar or 

7 Lift spring, safety valve HFS ≥ 2.5 bar 

8 Flash trap (ET); not required in systems > 300 kW if, 

instead, a high limit safety cut-out ≤ 110 °C and a 

maximum pressure limiter per boiler is additionally 

provided 

9 Maximum pressure limiter 

10 Pressure gauge 

11 Low water indicator (not in systems ≤ 300 kW). 

Alternatively one minimum pressure limiter or a 

replacement measure approved by the manufacturer is 

provided for each boiler 

12 Non-return valve 

13 Boiler drain & fill valve (KFE) 

14 Expansion line 

15 Shut-off valve with lockout against unintentional closure, 

e.g. by sealed cap valve 

16 Drain upstream of diaphragm expansion vessel 

17 Diaphragm expansion vessel (DIN-EN 13831) 

1) The maximum achievable flow temperature in combination 

with Logamatic control units is approx. 18 K lower than the 

shutdown temperature (high limit safety cut-out). 


1 

2 

4 1) 

> 300 kW 

5 1) 

15 

14 15 

2 13 

10 9 

P 

16 

13 

17 

VK 

RK 

6 720 640 417-14.1il

7.2.3 Arrangement of safety equipment to DIN-EN 12953-6; 

shutdown temperature (high limit safety cut-out) > 110 °C 

Shutdown temperature (high limit safety cut-out) 

> 110 °C, example 1 - direct heating 

6 720 640 417-15.1il 

Fig. 22 Safety equipment to DIN-EN 12953-6 for 

boilers with high limit safety cut-out > 110 °C; 

example: Maintaining pressure via a gas buffer 

The figures show the safety equipment to DIN-EN 12953- 

6 schematically for the system version – although other 

options are available. 

These figures only show versions where pressure is 

maintained via a gas buffer and a pressure maintaining 

pump. Additional versions which maintain pressure by 

means of various safety equipment can be identified in 

DIN-EN 12953-6. 

With high limit safety cut-out > 110 °C, long term 

requirements (e.g. regular inspections etc.) in accordance 

with the Health & Safety at Work Act must be observed. 

The practical implementation is subject to currently 

applicable technical rules. Implementing the system 

engineering with reference to the responsible supervisory 

authority is recommended. 


Shutdown temperature (high limit safety cut-out) 

> 110 °C, example 2 - direct heating 

Fig. 23 Safety equipment to DIN-EN 12953-6 for 

boilers with high limit safety cut-out > 110 °C; 

example: Maintaining pressure via a pressure 

maintaining pump 


RK Return 

VK Flow 

1 Hot water boiler 

2 Maximum pressure limiter [PSZ+A+] 

3 Pressure gauge 

4 Water level controller 

5 Flash trap 

6 Safety valve 

7 Minimum water level limiter [LSZ-A] 

8 Temperature limiter [TZA+A+] 

9 Temperature controller 

10 Temperature indicator 

11 Fill sample facility for checking the water level 

12 Shut-off valve - locked to prevent unintentional closing 

13 Sealed unvented expansion vessel 

14 Minimum pressure limiter [PSZ-A-] 

15 Non-return valve 

17 Shut-off valve 

18 Pipe to the sealed unvented expansion vessel 

19 Feed pump 

20 Heating facility 

22 Pressure maintaining pump 

23 Pressure regulator 

24 Automatic shut-off valve (N/C) 

25 Water level indicator 

26 Open vented expansion vessel 

27 Pressure maintaining valve - if N/C or if the actual pressure 

is lower than the minimum pressure, then item 24 may be 

omitted 

28 Shut-off valve with optional connection for test pressure 

gauge 

30 Minimum temperature controller (if required) 

31 Drainage system 


7 

6 720 640 417-16.1il

30 


7.3 Sizing and installation information 

7.3.1 Boiler circuit pump in the bypass as shunt pump 

Fig. 24 Sample hydraulic circuit for a single boiler system with boiler circuit pump in the bypass for Logano SK645 

and SK745 

FR Return temperature sensor 

KR Check valve 

PK Boiler circuit pump 

RK Return 

SR Actuator, return temperature raising facility 

SV Safety valve 

V HK Heating circuit flow rate 

VK Flow 

V PK Boiler circuit pump flow rate 


PK KR 

VK A B RK 

Boiler circuit pump flow rate V PK 

The boiler circuit pump, also referred to as a shunt pump, 

is required to regulate the return temperature (sensor 

flow). The boiler circuit pump can also be used to 

optimise the control characteristics. This makes it 

possible to minimise the switching events during the heatup 

process. This results in lower emissions. 

V PK 

Form. 2 Calculating the flow rate of the boiler circuit 

pump 

c Specific thermal capacityc = 1.16 × 10-3 kWh/(l × K) = 

1/860 kWh/(l × K) 

Δϑ K Temperature differential for sizing the boiler circuit pump 

30 K to 50 K (30 K for optimised heat-up characteristics) 

Q K Rated heat output in kW 

V PK Boiler circuit pump flow rate in l/h 

VSL 

SV 

QK = ------------------- 

ΔϑK × c 

SR 

E H 

C D 

V PK 

FR 

F 

G 

V HK 

90 °C 

70 °C 

6 720 640 417-17.1il 

Heating circuit flow rate V HK 

QHK VHK = 

--------------------------------- 

( ϑV – ϑR) × c 

Form. 3 Calculating the flow rate of the heating circuits 

c Specific thermal capacityc = 1.16 × 10-3 kWh/(l × K) = 

1/860 kWh/(l × K) 

QHK Heating circuit heat input demand in kW 

ϑR Heating circuit return temperature in °C 

ϑV Heating circuit flow temperature in °C 

VHK Heating circuit flow rate in l/h 


Total boiler flow rate VKges The boiler circuit pump head results from the following: 

• Boiler pressure drop at the selected flow rate VPK • Pipework pressure drop 

• Individual pressure drop values in the boiler circuit 

(Line: A–C–D–B, Fig. 24) 

The total boiler flow rate cannot simply be calculated by 

adding up the individual flow rates, because of the pump 

and system curves. However, as a first estimate, the 

simple addition is suitable to get an approximation of a 

solution. 

Form. 4 Calculating the total boiler flow rate 

VHK VKges V PK 

Base the sizing of the pipework in the boiler 

circuit on a flow velocity of 1 m/s to 1.5 m/s. 

VKges ≤ 

VPK + VHK Heating circuit flow rate in l/h 

Maximum total flow rate through the boiler in l/h 

(approximation) 

Boiler circuit pump flow rate in l/h 

Example 

Given: 

• Rated output QK = 1200 kW 

• Heating circuit flow temperature ϑV = 90 °C 

• Heating circuit return temperature ϑR = 70 °C 

• Temperature differential (selected) ΔϑK = 30 K 

Result: 

• VPK = 34400 l/h (Line: C–D, Fig. 24) 

• VHK = 51600 l/h 

(Lines: C–F, D–G and E–H, Fig. 24) 

• VKges ~ 86000 l/h 

(Lines: A–C and B–D, Fig. 24) 



7

32 


7.3.2 Boiler circuit pump as primary circuit pump 

B G 

V PK2 

SV 

SV 

VK A H RK VK A H RK 

VSL VSL 

Fig. 25 Sample hydraulic circuit for a 2-boiler system with boiler circuit pump as primary circuit pump for 


FR Return temperature sensor 

FVS Strategy flow temperature sensor 


RK Return 

SR Actuator, return temperature raising facility 

SV Safety valve 

V HK Heating circuit flow rate 

VK Flow 

V PK Boiler circuit pump flow rate 


Boiler circuit pump flow rate V PK 

For systems with primary circuit pumps (e.g. in the case of 

low loss headers or non-pressurised distributors) 

installing the boiler circuit pump into the return is 

recommended. 

Form. 5 Approximation formula with sizing factor for the 

flow rate of the boiler circuit pump in a single 

boiler system 

Form. 6 Approximation formula with sizing factor for the 

flow rate of the boiler circuit pump in a 2-boiler 

system 

Size of calculation for formula 5 and formula 6: 

VHK Heating circuit flow rate in l/h 

VKges Total flow rate of the boiler circuit in l/h 

In 2-boiler systems, split the pump rate of the boiler circuit 

pumps according to the respective boiler output. Where 

several heating circuits are constantly operated with high 

flow temperatures and maximum flow rate, the flow rate of 

each boiler circuit pump should correspond to the flow 

rate of the heating circuit pumps. For systems with gas 

condensing boilers, there are special requirements, e.g. 

SR2 

PK2 

VKges, 1 = VHK × (1,0 ... 1,2) 

VKges, 2 = 

VHK × (1,2 ... 1,5) 

C D 

B G 

V PK1 

F 

SR1 

PK1 

FR2 FR1 

E 

FVS 

90 °C 

70 °C 

maintenance of as low a return temperature as possible. 

The pump rate of the boiler circuit pump may need to be 

adjusted to the pump rate of the heating circuits. 

Sizing the 3-way valve 

Size the 3-way valve for the respectively calculated flow 

rate. For this, observe the pressure drop when the valve is 

fully open, as the control quality is influenced by the 

proportional pressure drop. 

Primary circuit pump head 

The boiler circuit pump head results from the following: 

• Boiler pressure drop at the selected flow rate V PK 

• Pipework pressure drop 

• Individual pressure drop values in the boiler circuit 

(Line: A–D–E–H, Fig. 25) 

Example 

Given: 

• Heating circuit heat input demand SQHK = 4000 kW 

• Heating circuit flow temperature ϑV = 90 °C 

• Heating circuit return temperature ϑR = 70 °C 

• Sizing factor (selected) = 1.3 

• Heating circuit flow rate VHK = 172000 l/h 

Result: 

• VKges = VHK × 1.3 = 172000 l/h × 1.3 = 223600 l/h 

(lines: C–D and E–F, Fig. 25) 

The total flow rate calculated for the boiler side should be 

split according to the rated output (in this case 50/50 %): 

• Boiler circuit pump flow rate 

VPK = 111800 l/h 

(lines: A–C, B–G and F–H, Fig. 25) 


V HK 

6 720 640 417-18.1il

7.3.3 Low loss header 

A low loss header (hydraulic balancing line) is designed to 

provide hydraulic separation between the boiler circuit 

and the heating circuits. 

Installing a low loss header brings many benefits: 

• Sizing boiler circuit pump and actuators is made easy. 

• Mutual influencing between the heating water flow 

inside the boiler and in the heat consumer circuits is 

prevented. 

• Boiler and heat consumers are only supplied with the 

assigned water flow. 

• May be used in single and multi-boiler systems, subject 

to the heating circuit control system. 

• Actuators on both sides of the low loss header provide 

optimum operation if they are sized correctly. 

• The hydraulic balancing line can also be used as a 

sludge trap, subject to being sized correctly 

( page 26). 

• Where there is a major pressure drop on the water side 

and with large distances between boiler and heating 

circuits, a split into primary and secondary side is 

possible. 

Sizing the low loss header 

Correct sizing is crucial to the function of the low loss 

header. To safeguard a good separation with 

simultaneous function as a sludge trap, size the pipework 

so that there is practically no pressure drop between the 

flow and return. At the nominal amount of water, a flow 

velocity of 0.1 m/s to 0.2 m/s can be expected. This also 

enables the simultaneous use as a sludge trap. To be able 

to capture the heating circuit flow temperature, provide a 

sensor well of 200 mm to 300 mm length in the upper 

area of the hydraulic balancing line on the heating circuit 

side. 

D 

= 

VK,ges 1 

-------------- × ------------v 

2827 

Form. 7 Calculating the size of the low loss header 

D Diameter of the hydraulic balancing line in m 

v Flow velocity in m/s 

VKges Total flow rate of the boiler circuit in m3/h 


Example 

Given: 

• Total flow rate VKges = 223.6 m3 /h 

• Flow velocity (assumption) v = 0.2 m/s 

Result: 

• Diameter of the hydraulic balancing line 

D ~ 0.63 m 

Fig. 26 Main diagram of a low loss header 

RH Heating system return 

RK Return 

VH Heating system flow 

VK Flow 

1 Female connection for one air vent valve 

2 Female connection for a sensor well ½ " 

3 Perforated divider 

4 Quick-action shut-off valve 


VK 

RK 

4 

D 1 

2 

3 

VH 

5 × D 

RH 

3–4 × D 

D 

6 720 640 417-19.1il 

7

34 


7.4 Single boiler system Logano SK645 and SK745 with boiler control unit 

Fig. 27 System example Logano SK645 and SK745 

FB DHW temperature sensor 

FK Boiler water temperature sensor 

FV Flow temperature sensor 

FZ Auxiliary temperature sensor 

HK Heating circuit 


PH Heating circuit pump 


PS Cylinder primary pump 

PZ DHW circulation pump 

RK Return 

SH Heating circuit actuator 

SK Boiler circuit actuator 

VK Flow 

1) Number and layout of the heating circuits subject to the 


The circuit diagram is only a schematic 

illustration. 

Information for all system examples page 26. 

FB 

PZ 

KR 

PS 

KR 

FK 

SK 

PK 

VK RK 

Logano SK645, SK745 

FZ 

HK1 

Application range 

• Logano SK645 and SK745 boilers 

• Boiler control with a conventional Logamatic 4212 

control unit and ZM427 auxiliary module 

• Boiler circuit control with Logamatic 4321 control unit 

in conjunction with a third party heating circuit 

controller or with special applications 

Function description 

The Logamatic control unit safeguards the minimum boiler 

return temperature. If the actual return temperature 

captured by the FZ temperature sensor falls below the set 

value whilst the burner is switched on, the control unit 

reduces the system flow rate towards the boiler by 

switching the SK boiler circuit actuator. At the same time, 

hot water from the flow is mixed into the cold water 

returning from the system to achieve the set return 

temperature. 

The boiler circuit actuator is opened towards the 

consumer circuits once the minimum return temperature 

has been reached. 

Special engineering information 

• This arrangement is ideally suited for a modernised 

system where the heating circuit control is provided by 

the higher ranking control (third party control unit). 

• This requires an FZ auxiliary temperature sensor. 


HK2 

FV1 FV2 

PH1 

PH2 

SH1 

SH2 

M M 

1) 

6 720 640 417-20.1il

Selection of control equipment 

Logamatic 4212 control unit 

6 720 640 417-41.1il 

Logamatic 4212 (possible full complement) 

blue auxiliary equipment 

Logamatic 42121) conventional control unit for mounting inside the 

boiler for operation with a constant boiler water temperature with 

TR (90/105 °C) temperature controller; for switching single and 

2-stage burners, with adjustable high limit safety cut-out (100/110/ 

120 °C). Including burner cable, stage 2. 

Standard equipment 

Safety equipment 

ZM425 – Central module as display, incl. thermometer and burner 

fault indicator, with two slots for hours run meter for burner stages 1 

and 2 

Auxiliary equipment 

ZM426 – Auxiliary module for the use of a second high limit safety 

cut-out, set to 100 °C without flash trap 

ZM427 – Auxiliary module to safeguard the boiler operating 

conditions for low temperature boilers with minimum return 

temperature, for steel boilers and gas condensing boilers with external 

condensing heat exchanger (actual flow temperature control) and to 

provide a hydraulic shut-off in multi-boiler systems, incl. flow 

temperature sensor 

ZB – Hours run meter 

Sensor well R½ , 100 mm long for Logamatic cylindrical sensors 

Tab. 8 Optional equipment for the Logamatic 4212 

control unit in connection with the system 

example in Fig. 27 

1) For boiler water temperatures in excess of 80 °C set the high 

limit safety cut-out to 110 °C or 120 °C 

The technical documents of the control units include 

detailed information. 



6 720 640 417-42.1il 



Logamatic 43211) for a single boiler system or as the master control 

unit for the first boiler in a multi-boiler system, with TR (90/105 °C) 

temperature controller and adjustable high limit safety cut-out (100/ 

110/120 °C), for switching single stage, 2-stage or modulating 

burners. Including burner cable, stage 2, boiler water and outside 

temperature sensors. Can accommodate up to four function modules. 



CM431 – Controller module 

ZM432 – Central module for switching burners and boiler circuit 

functions; with manual operating level 

MEC2 – Digital programming unit for setting parameters and 

checking the control unit; integral room temperature sensor and radio 

clock receiver 




FM441 – Function module for one heating circuit with mixer and 

one DHW circuit with DHW circulation pump; incl. DHW temperature 

sensor (up to one module per control unit) 

FM442 – Function module for two heating circuits with mixer; incl. 

one FV/FZ sensor set (up to four modules per control unit) 

Room installation set with wall retainer for MEC2 programming unit 

and boiler display 

Online set with online cable and wall retainer for MEC2 programming 

unit 

BFU – Remote control incl. room temperature sensor for controlling 

a heating circuit from the living space 

BFU/F – Remote control like the BFU, but with an integral radio 


Separate room temperature sensor for BFU and BFU/F remote 

control units 

FV/FZ – Sensor set with flow temperature sensor for heating circuits 

with mixers or auxiliary temperature sensors for boiler circuit functions; 

incl. connection plug and accessories 

FG – Flue gas temperature sensor for a digital display of the flue 

gas temperature; in a stainless steel sleeve; version suitable for 

positive pressure 








7


7.5 Single boiler system with Logano SK645 and SK745 boilers: 

Logamatic Boiler and heating circuit control with hydraulic separation 

Fig. 28 System example for Logano SK645 and SK745 with Logamatic boiler and heating circuit control and hydraulic 

separation 








RK Return 


THV Thermostatic valve 

VK Flow 

VR Return distributor 

VV Flow distributor 

WH Low loss header 

1) Alternative to low loss header (WH) 

36 

FK 



• Logamatic boiler and heating circuit control 

• Hydraulic separation 

• Systems are laid out this way, if a feed pump is 

required, e.g. as a result of the sizing of the heating 

circuit pumps or if several distributor stations are 

required or if the distributor stations are installed at 

greater distances. 

Brief description of the system 

• Control of the minimum return temperature by xxxx of 

the heating circuit actuators 

• 2-stage or modulating burner operation 

• Simple layout 

KR 

PK 

VK RK 



illustration. 


FZ 

FK 

WH 

THV 

FV 

PH 

SH 

HK 


The heating circuits are controlled via heating circuit 

modules. To achieve a raising of the return temperature, 

the switching of the heating circuit actuators is given a 

higher ranking order. The heating water flow rate to the 

boiler remains at a reduced level until the set return 

temperature is achieved by the flow water being mixed via 

the hydraulic separation. The heating circuit control will 

then be enabled again. 


• Size the boiler circuit pump for the maximum calculated 

flow rate and the pressure drop in the boiler circuit. 

Switch the pump to constant operation or with a run-on 

time of 60 minutes. 

• Allow for a low loss header or, alternatively, a 

distributor with bypass and non-return valve. 

• In conjunction with Logamatic control units, the 

maximum possible flow temperature for a heating 

circuit with mixer is 90 °C. 


VV 

VR 

1) 

KR 

6 720 640 417-46.1il



6 720 640 417-42.1il 




























unit 






control units 

















7

38 


7.6 Single boiler system with Logano SK645 and SK745 with boiler and heating circuit 

control 











RK Return 


VK Flow 

1) 

Number and layout of the heating circuits subject to the 


FB 

PZ FK VK RK 


illustration. 


KR 

PS 

KR 


FZ 

FV1 

PH1 

SH1 

HK1 

FV2 

PH2 

SH2 

M M 



• Boiler and heating circuit control (heating circuits with 

actuator) with Logamatic 4321 control unit 


The Logamatic 4321 control unit safeguards the minimum 

boiler return temperature. If the actual return temperature 

captured by the FZ temperature sensor falls below the set 

value whilst the burner is switched on, the control unit 

reduces the system flow rate towards the heating circuit 

as a result of the higher ranking switching of the SH boiler 

circuit actuators. At the same time, hot water from the flow 

is mixed into the cold water returning from the system to 

achieve the set return temperature. 

When the minimum return temperature has been reached, 

the system switches over to heating circuit control. 




1) 

HK2 

6 720 64 0 417-21.1il



6 720 640 417-42.1il 




























unit 






control units 







Sensor well R½ ,100 mm long for Logamatic cylindrical sensors 










7

40 


7.7 Single boiler system with Logano SK645 and SK745 with boiler and heating circuit 

control as well as hydraulic balancing 







HW Low loss header 






RK Return 



VK Flow 

1) 

FB 



PS 


illustration. 


PZ 

KR 

KR 

FK 

PK 

VK RK 


SK 

M 

FZ 

HW 

HK1 



• Boiler control with a conventional Logamatic 4212 

control unit plus ZM427 auxiliary module 

• Heating circuit control and DHW heating by means of 

the higher ranking control unit or constant temperature 

mode 


The Logamatic 4212 control unit safeguards the minimum 

boiler return temperature via the ZM427 auxiliary module. 

If the actual return temperature captured by the FZ 

temperature sensor falls below the set value whilst the 

burner is switched on, the control unit reduces the system 

flow rate towards the boiler by switching the SK boiler 

circuit actuator. At the same time, hot water from the flow 


achieve the set return temperature. Once the minimum 

return temperature has been reached, the boiler circuit 

actuator opens towards the consumer circuits. 






• The boiler circuit flow rate must be greater than the 

heating circuit flow rate. 


HK2 

FV1 FV2 

PH1 

PH2 

SH1 

SH2 

M M 

1) 

6 720 640 417-22.1il



6 720 640 417-41.1il 



Logamatic 42121) conventional control unit for mounting inside the 

boiler for operation with a constant boiler water temperature with 

TR (90/105 °C) temperature controller; for switching single and 

2-stage burners, adjustable high limit safety cut-out (95/100/110/ 

120 °C). Including burner cable, stage 2. 



ZM425 – Central module as display, incl. thermometer and burner 

fault indicator, with two slots for hours run meter for burner stages 1 

and 2 




ZM427 – Auxiliary module to safeguard the boiler operating 

conditions for low temperature boilers with minimum return 

temperature, for steel boilers and gas condensing boilers with external 

condensing heat exchanger (actual flow temperature control) and to 

provide a hydraulic shut-off in multi-boiler systems, incl. flow 

temperature sensor 

ZB – Hours run meter 











7

42 


7.8 2-boiler system with Logano SK645 and SK745 with boiler and heating circuit 

control plus hydraulic balancing 

FB 

KR 














RK Return 



VK Flow 



2) 

Alternative to low loss header 

3) Logano SK645 and SK745 with return temperature 

raising facility 



• Boiler circuit control with Logamatic 4321 and 4322 

control units and FM458 strategy module in 

conjunction with a third party heating circuit controller 

or with special applications 

FVS 

SK2 SK1 

M 

M 

FZ 3) 

PK2 PK1 

PZ FK2 VK RK 

FK1 VK RK 

KR 

PS 


illustration. 


(2) 

Logano SK645, SK745 Logano SK645, SK745 

(1) 

HW 

FZ 3) 


Both boilers can be hydraulically isolated via the SK boiler 

circuit actuator. The boiler sequence can be switched 

according to load or time by means of the strategy 

module. Sequence reversal and operation in parallel or 

series can be selected by means of settings at the control 

unit. The lead boiler (1) starts when the actual 

temperature captured by the FVS strategy sensor falls 

below the set flow temperature. If the heat demand 

increases, the lag boiler (2) is automatically started and 

the SK boiler circuit actuator opens. With dropping load, 

the switching events are reversed. 

If the actual return temperature captured by the FZ 


burner is switched on, the control unit reduces the system 

flow rate towards the boiler by switching the SK boiler 

circuit actuator. At the same time, hot water from the flow 


achieve the set return temperature. 








• A low loss header can also be used to provide sludge 

removal. 

• A low-pressure distributor with bypass can be used as 

an alternative to the low loss header. 



HK1 

HK2 

FV1 FV2 

PH1 

PH2 

SH1 

SH2 

M 

M 

1) KR 

2) 

6 720 640 417-25.1il



6 720 640 417-42.1il 




























unit 






control units 

















6 720 640 417-44.1il 



Logamatic 43221) as lag control unit for a second and third boiler in a 

multi-boiler system, with TR (90/105 °C) temperature controller and 

adjustable high limit safety cut-out (100/110/120 °C), for switching 

single stage, 2-stage or modulating burners. Including burner cable, 

stage 2 and boiler water temperature sensors. Can accommodate up 

to four function modules. 






Boiler display to display the boiler water temperature at the control 

unit; may be extended with further modules 




MEC2 – Digital programming unit in place of the boiler display for 

setting parameters and checking the control unit; integral room 

temperature sensor and radio clock receiver 







unit 






control units 




FA – Additional outside temperature sensor (up to one per 

control unit) 











7

44 


7.9 2-boiler system with Logano SK645 and SK745 with boiler and heating circuit 

control plus hydraulic balancing 

FB 

PZ 

KR 

PS 

KR 




FRS Strategy return temperature sensor 








PS Cylinder primary pumps 


RK Return 


VK Flow 

KR 

PK2 



2) Alternative to low loss header 



• Boiler and heating circuit control (heating circuits with 

actuator) with Logamatic 4321 or 4322 control unit 

and FM458 strategy module 


The boiler sequence can be switched on the basis of load 

and time by means of the strategy module. Sequence 

reversal and operation in parallel or series can be selected 

by means of settings at the control unit. The lead boiler (1) 

starts when the actual temperature captured by the FVS 

KR 

PK1 

FK2 VK RK 

FK1 VK RK 

(2) 



illustration. 


(1) 


FRS 

HW 

FVS 

strategy sensor falls below the set flow temperature. The 

lag boiler is hydraulically isolated by the KR check valve in 

the boiler flow. If the heat demand increases, the lag boiler 

(2) is automatically started. With dropping load, the 

switching events are reversed. 

The Logamatic control unit safeguards the actual return 

temperature for both boilers. If the actual return 

temperature captured by the FRS strategy return 


burner is switched on, the control unit reduces the heating 

circuit flow rate towards the boiler as a result of the higher 

ranking switching of the SH boiler circuit actuators until 

the operating temperature has been reached. 


• The PK feed pumps, together with hydraulic balancing 

are recommended for several distributor stations or 

those that are far apart. A low loss header or, 

alternatively, a low-pressure distributor with bypass 

and check valve can be used to provide hydraulic 

balancing. 

• A low loss header can also be used to provide sludge 

removal. 

• Split the total output 50 % over both boilers. Where a 

different output distribution applies, safeguard the 

respective flow rates by suitable measures (pipe sizing 

and/or balancing valves). Pipework according to 

Tichelmann is recommended. 

• This requires an FZ auxiliary temperature sensor 

(as FRS strategy return temperature sensor). 


HK1 

FV1 

PH1 

SH1 

M 

FV2 

PH2 

SH2 

HK2 

M 

1) 

KR 

2) 

6 720 640 417-26.1il



6 720 640 417-42.1il 




























unit 






control units 

















6 720 640 417-44.1il 




























unit 






control units 





control unit) 











7

46 


7.10 2-boiler system with Logano SK645 and SK745 as well as Logano plus SB315 and 

SB615 gas condensing boilers with boiler and heating circuit control 

FW2 

FW3 

PZ 

KR 

Fig. 33 System example Logano SK645 and SK745 as well as Logano plus SB315, SB615 and SB735 

EK Cold water inlet 



FW DHW temperature sensor 







PW Stratification pump 


RK Return 



VK Flow 

WT Heat exchanger 

M 

PS 

KR 

FW1 

1) 



2) Inspection bypass 


• Logano plus SB315, SB615 and SB735 gas 

condensing boilers 


• Boiler circuit control with Logamatic 4321 and 4322 

control units and FM447 strategy module, also in 

conjunction with a third party heating circuit controller 

or with special applications 


The boiler sequence can be switched on the basis of load 

and time by means of the FM447 strategy module. The 

lead boiler (1) starts when the actual temperature 

PW 

EK 

WT 

FK2 

FVS 

PK 

VK RK 

(2) 



illustration. 


M 

SK 

FZ 

2) 

VK 

RK 

(1) 

FK1 

Logano plus 

SB315, SB615, 

SB735 

PH1 

SH1 

captured by the strategy flow temperature sensor falls 

below the set flow temperature. If the heat demand 

increases, the lag boiler (2) is automatically started. 

If the gas condensing boiler is connected in series to the 

low temperature boiler downstream, the required return 

temperature raising will be provided mainly by the gas 

condensing boiler. 

If the actual return temperature captured by the auxiliary 

temperature sensor falls below the set value even though 

the burner is switched on, the control unit reduces the 

system flow rate towards the low temperature boiler by 

switching the boiler circuit actuator. At the same time, hot 

water from the flow is mixed into the cold water returning 

from the system to achieve the set return temperature. 





• The boiler sequence cannot be reversed. 

• Size the heating circuit pumps in accordance with the 

calculated maximum pressure drop in the heating and 

boiler circuit. The boiler circuit pump overcomes the 

pressure drop in the lag boiler at the maximum boiler 

flow rate. 

• It is recommended to split the total output in 

proportions of 50 % to 60 % for the gas condensing 

boiler and 40 % to 50 % for the low temperature boiler. 

• This requires an auxiliary temperature sensor. 

• Implement the connections so that the boiler can 

operate independently to ensure an emergency 

provision during service/maintenance. 


HK1 

FV1 FV2 

PH2 

SH2 

M M 

HK2 

1) 

6 720 640 417-39.1il



6 720 640 417-42.1il 




























unit 






control units 

















6 720 640 417-44.1il 




























unit 






control units 





control unit) 











7

48 

8 Delivery and installation information 

8 Delivery and installation information 

8.1 Delivery method 

The boiler block can be transported on its base frame, e.g. 

using rollers. It is possible to transport the blocks of the 

Logano SK645 and SK745 boilers with forklift trucks, 

with forks inserted above the base frame. When 

transporting the blocks of the Logano SK645 and SK745 

boilers with a crane, use only the holes in the gusset 

plates. 

Content of packaging 

Boiler block with burner 

door 

Logano SK645 

and SK745 

1 transport unit 1) 

Insulated boiler jacket 1 wooden crate 

Burner 2) 

1 Cardboard box 

Control unit2) 1 Cardboard box 

Tab. 19 Delivery Logano SK645 and SK745 

1) SK745 with 1400 kW and 1850 kW output are respectively 

supplied as two packing units each 

2) Not part of the standard boiler delivery 

8.2 Installation information 

Pipework 

• Ensure the boiler can be adequately vented. 

• In open vented systems, route pipework with a slope 

towards the expansion vessel. 

• Never allow for pipe reductions in horizontal pipe runs. 

• Lay pipes without stress. 

Electrical installation 

A permanent connection in line with VDE 0100, 

VDE 0116 and VDE 0722 is required [in Germany]. 

Observe local regulations. 

• Take care to ensure correct cable and capillary pipe 

routing. 

Commissioning 

Check the quality of the fill and top-up water. 

• Flush the entire heating system before filling with 

heating water. 

Tightness test 

Check the system for leaks in accordance with 

DIN 18380. The test pressure is 1.3-times the operating 

pressure, but at least 1 bar. 

• Separate safety valve from expansion vessel (in sealed 

unvented systems) before pressure testing. 

Handover 

On handover, make operators familiar with the system 

functions and its operation; and give them the technical 

documentation. 

• Draw attention to any special considerations regarding 

maintenance; a maintenance and inspection contract is 

recommended. 


9 Installation location 

9.1 General requirements of the installation room 

9.1.1 Combustion air supply 

The installation room and the siting of gas appliances 

should meet the conditions specified by the respective 

national, regional or local bodies appertaining to boiler 

rooms and must comply with relevant fire regulations. 

For open flue combustion equipment with a total rated 

output in excess of 50 kW, the combustion air supply is 

deemed to be ensured if a vent to the outside with a clear 

opening of at least 150 cm 2 (plus 2 cm 2 for every kilowatt 

output above 50 kW rated output) is provided. The 

required cross-section may be split over up to two lines 

and must be sized to provide the equivalent air flow rate. 

General requirements 

• Combustion air vents and lines must never be closed 

or covered unless there is special safety equipment 

that ensures the combustion equipment can only be 

operated if the flow cross-section is unobstructed. 

• The required cross-section must not be restricted by a 

closure or grille. 

• An adequate supply of combustion air can also be 

verified by other means. 

• Observe special requirements appertaining to 

combustion equipment operated with LPG. 

9.1.2 Siting combustion equipment 

Gas combustion equipment with a total rated output in 

excess of 50 kW must only be sited in rooms 

• that are not used for any alternative purpose 

• that have no opening towards other rooms, except 

doors 

• the doors of which are tight and self-closing 

• that can be vented 

The burner and flue supply facilities of the combustion 

equipment must be able to be switched off at any time by 

means of an emergency stop switch located outside the 

installation room. Provide a sign adjacent to the 

emergency stop switch that reads as follows: 

“EMERGENCY STOP SWITCH - COMBUSTION 

EQUIPMENT”. 

Notwithstanding these rules, combustion equipment 

may also be installed in other rooms, provided that: 

• the use of these rooms makes this necessary and the 

combustion equipment can be operated safely or 

• the rooms are in freestanding buildings that only serve 

to operate the combustion equipment and fuel storage. 

Installation location 

Open flue combustion equipment must not be installed: 

• in stairwells, except in residential buildings with no 

more than two apartments 

• in generally accessible hallways that serve as escape 

routes 

• in garages 

In rooms with systems that extract air 

Open flue combustion equipment must only be installed in 

rooms equipped with systems that extract air subject to 

the following conditions: 

• simultaneous operation of the combustion equipment 

and the air extractor systems will be prevented by 

safety interlocks 

• flue gas routing is monitored by appropriate safety 

equipment 

• flue gas will be routed via the air extractor systems or it 

will be ensured that such systems cannot create 

dangerous negative pressure. 

Gas shut-off facility 

A thermally-activated shut-off facility (TAE) must be 

installed immediately upstream of the gas combustion 

equipment. 


9

50 

9 Installation location 

9.2 Handling details 

The stated values correspond to the boiler in its delivered 

condition. For tight spaces, the front door can be 

removed. 

Logano 



Boiler 

size 

Minimum 

length 

Minimum 

width 

Minimum 

height 

Minimum 

weight 

1) The weight in operation includes the weight of the boiler, its water content, the control unit, burner, gas ramp and fittings 

Weight in 

operation 1) 

[kW] [mm] [mm] [mm] [kg] [kg] 

120 1295 700 1005 447 618 

190 1490 760 1065 554 792 

250 1620 790 1095 642 912 

300 1780 790 1095 691 993 

360 1773 860 1165 817 1185 

420 1973 860 1165 899 1319 

500 1913 950 1255 1063 1552 

600 2163 950 1255 1158 1715 

730 2130 1060 1365 1401 2068 

820 2330 1060 1365 1504 2244 

1040 2390 1170 1475 1852 2744 

1200 2690 1170 1475 2024 3041 

1400 2990 1320 1612 2690 4109 

1850 3410 1400 1732 3540 5400 

Tab. 20 Logano SK645 and SK745 handling dimensions 


9.3 Installed dimensions 

A S 

A V 

Fig. 34 Installation room for Logano SK645 and SK745 

boilers 

1) For the SK745 1400 kW and 1850 kW, the control unit is 

mounted on the l.h. or r.h. side 

1) 

A H 

A S 

6 720 640 417-27.1il 

Logano Boiler size Clearance A H Clearance A V 1) 



1) Observe dimension L BR (burner length) relative to clearances A V and A S (on the closure side of the burner door) 

Installation location 

When installing your boiler maintain the 

recommended minimum dimensions. Select 

the recommended wall clearances to enable 

easy access for installation, maintenance and 

service work. 

Site the boiler only in rooms that comply with 

the local regulations appertaining to the 

siting of boilers. The room must be large 

enough to ensure access to the boiler in line 

with local regulations. 

Clearance A S 

[kW] [mm] [mm] [mm] 

120–300 1000 2000 250 + L BR 

360–600 1000 2100 250 + L BR 

730–1200 1000 2200 250 + L BR 

1400–1850 2) 

Tab. 21 Specified wall clearances 

2) Allow for an additional 230 mm on the side where the control unit is mounted. 

1000 2500 250 + L BR 


9

52 

10 Additional equipment and accessories 


10.1 Additional safety equipment to DIN-EN 12828 

DIN-EN 12828 specifies a low water indicator to protect 

the boiler against excessive heating. 

10.1.1 Safety equipment 

In accordance with the currently valid Pressure 

Equipment Directive (PED), all facilities and pipework 

connected to boilers that are part of heating systems with 

safety temperatures in excess of 110 °C are considered 

part of the boiler. That means that all components 

between the shut off facilities (e.g. slider valves) in the 

flow and return as well as the boiler flow and return must 

be approved. This also concerns intermediate flow pieces 

and valve manifolds to which safety equipment can be 

fitted. Subject to the safety level (for this see 

DIN-EN 12828 and DIN-EN 12953-6), install different 

safety equipment at the various connections. 

The boiler safety assemblies are approved to Pressure 

Equipment Directive 97/23/EC (TS = 120 °C, 

PS = 16 bar). They are suitable in accordance with 

DIN-EN 12828 for a maximum operating temperature of 


versions 

+ Applicable 

– N/A 

tR ≤ 105 °C, high limit safety cut-out with 

shutdown temperature ≤ 110 °C 

to DIN-EN 12828 

Low water indicator 

For the Logano SK645 and SK745 low temperature 

boilers install a low water indicator or minimum pressure 

limiter in line with DIN-EN 12828. 

105 °C. Equipment for higher operating temperatures to 

DIN-EN 12953-6 on request. 

In systems to DIN-EN 12828, the Logano SK645 and 

SK745 low temperature boilers can be equipped with a 

safety assembly (accessory). This comprises an 

intermediate flow piece, valve manifold, minimum 

pressure limiter (low water indicator to DIN-EN 12828), 

manostat pipe with shut-off valve and 0–16 bar pressure 

gauge. Furthermore, it features three additional available 

connections R½ for the connection of further pressure 

limiters as well as two additional available connections 

R½ at the intermediate flow piece, e.g. for thermometer 

and high limit safety cut-out. 

Boiler safety assemblies are available in the following 

sizes: DN65, DN80, DN100, DN125, DN150 and 

DN200. 

High limit safety cut-out1) with shutdown 

temperature > 110 °C, 

≤ 120 °C to DIN-EN 12953-6 

Heat source Heat source 

≤ 300 kW > 300 kW ≤ 300 kW > 300 kW 

Maximum pressure limiter – + + + 

High limit safety cut-out set and 

maximum pressure limiter 

– + 2) 

– – 

Minimum pressure limiter + 3) 

– – – 

Minimum pressure limiter – -4) + + 

Low water indicator + + – – 

Tab. 22 Safety equipment versions for Logano SK645 and SK745 

1) It is recommended to implement the system engineering with reference to the responsible supervisory authority. Observe the Pressure 

Equipment Directive (PED) and the Health & Safety at Work Act [Germany] 

2) Where the flash trap to DIN-EN 12828 is omitted in systems with tR ≤ 105 °C (high limit safety cut-out 110 °C) 

3) As manufacturer-tested replacement measure for low water indicator to DIN-EN 12828 in system with tR ≤ 105 °C (high limit safety cut-out 

110 °C) 

4) Replacement for low water indicator to DIN-EN 12828 in system with t R ≤ 105 °C (high limit safety cut-out 110 °C) 

Safety component Make Component ID 

Maximum pressure limiter Sauter DSH 143 F 001 SDB.00-331 

Minimum pressure limiter Sauter DSL 143 F 001 SDWF00-330 

High limit safety cut-out Sauter RAK 13.4040 B STB 10 602 000 

Minimum pressure limiter Fatini Cosmi2B01ATF0.8 WB 40 28 65 19 

Tab. 23 Approval ID for safety components for the Logano SK645 and SK745 


700 

H 1 

B 

Additional equipment and accessories 

Fig. 35 Boiler safety assembly with intermediate flow piece Logano SK645 and SK745 (dim. in mm) 

1 Pressure gauge 0–16 bar 

2 3 available connections R½ for the connecting of 

additional pressure limiters 

3 Minimum pressure limiter Sauter DSL143-F001 

(low water indicator to DIN-EN 12828) 

Fig. 36 Intermediate return piece for Logano SK645 and SK745 (dim. in mm) 

510 

1 Flange connection for expansion line 

2 R½ connection for thermometer or temperature sensor 

A 

1 2 3 


4 

5 

4 

H 2 

H 3 

10 

4 Two available connections R½ on the intermediate flow 

piece (e.g. for thermometer and high limit safety cut-out 

5 Manostat pipe with shut-off valve 

160 

6 720 640 417-28.1il 

Logano Boiler size Type A B H1 H2 H3 [kW] [mm] [mm] [mm] [mm] 

120–300 VZ65 DN65/PN 16 450 600 330 500 


360–420 VZ80 DN80/PN 16 450 575 330 500 

500–600 VZ100 DN100/PN 16 460 555 330 480 

730–1200 VZ125 DN125/PN 16 475 555 330 480 


1400 VZ150 DN150/PN 16 490 530 330 480 

1850 VZ200 DN200/PN 16 515 530 330 480 

Tab. 24 Dimensions, boiler safety assembly with intermediate flow piece for Logano SK645 and SK745 

2 

2 

A 1 

B 

1 

A 2 

H 2 

H 1 

160 

160 

6 720 640 417-29.1il 

Logano Boiler size Type A1 A2 B H1 H2 [kW] [mm] [mm] [mm] 

120–300 RZ65 DN65/PN 16 DN32/PN 40 135 350 175 


360–420 RZ80 DN80/PN 16 DN40/PN 40 145 350 175 

500–600 RZ100 DN100/PN 16 DN50/PN 40 160 350 175 

730–1200 RZ125 DN125/PN 16 DN65/PN 16 225 350 175 


1400 RZ150 DN150/PN 16 DN65/PN 16 240 350 175 

1850 RZ200 DN200/PN 16 DN80/PN 16 270 400 200 

Tab. 25 Dimensions, intermediate return piece for Logano SK645 and SK745


10.2 Additional noise attenuating equipment 

10.2.1 Requirements 

Necessity and extent of noise attenuating measures are 

subject to the noise level and the disturbance created. 

Buderus offers three facilities to attenuate noise that are 

specifically tailored to the low temperature boilers; these 

can be supplemented by further on-site noise protection 

measures. On-site measures include pipe fixings that are 

equipped with structure-borne noise insulators, 

compensators in the connection pipes and flexible 

connections to the building. Noise attenuating facilities 

require additional space that must be taken into account 

at the engineering stage. 

10.2.2 Boiler support with structure-borne noise 

insulation 

Boiler supports that insulate structure-borne noise 

prevent a transfer of structure-borne noise to the 

foundations and the building. They comprise U-profile 

rails into which Ω-shaped bent longitudinal insulation 

brackets have been set ( Fig. 37 and Fig. 38). The 

longitudinal insulation brackets are made from spring 

steel and are coated with a silencing compound to 

prevent the radiation of air-borne noise. Under load these 

flex approx. 5 mm. When engineering boiler supports with 

structure-borne noise insulating properties, take into 

account that the installed height of the boiler and 

consequently the location of connections to the pipework 

will alter accordingly ( Tab. 26, page 55). To 

compensate for the flexing distance of the longitudinal 

insulation brackets, and to further minimise the 

transmission of sound via the water connections, the 

installation of pipe compensators in the heating water 

pipes is also recommended. 

54 

6 720 640 417-30.1il 

Fig. 37 Example of boiler supports that insulate against 

structure-borne noise 


Additional equipment and accessories 

Fig. 38 Boiler support that insulates against structure-borne noise for Logano SK645 and SK745 (dim. in mm) 

1 Side catch 

2 Longitudinal insulation bracket 

1) Flex under load approx. 5 mm 

1 

2 

Logano Boiler 

size 



44 

1) 

Plinth 

dimensions / 

Foundation 

dimensions 

Length 

L SO 

Width 

B SO 

A B 

B SO 

B S 

B B 


L S 

L SO 

U-profile rail Dimensions of longitudinal 

insulation bracket 

Length 

L S 

Width 

B S 

Clearance 

A B 

6 720 640 417-31.1il 

10 

Lengths Weight 

[kW] [mm] [mm] [mm] [mm] [mm] [mm] [kg] 

120 915 700 1060 60 700 4 × 250 10.0 

190 1110 760 1060 60 760 4 × 250 10.0 

250 1240 790 1060 60 790 4 × 250 10.0 

300 1400 790 1360 60 790 2 × 250 + 2 × 312.5 15.0 

360 1373 860 1385 60 860 4 × 500 20.0 

420 1573 860 1385 60 860 4 × 500 20.0 

500 1503 950 1480 60 950 2 × 750 + 2 × 500 9.6 

600 1753 950 1560 60 950 2 × 1000 + 2 × 500 15.0 

730 1700 1060 1560 60 1060 2 × 1000 + 2 × 500 15.0 

820 1900 1060 1900 120 1060 4 × 500 15.0 

1040 1960 1170 1900 120 1170 4 × 500 15.0 

1200 2260 1170 2120 120 1170 4 × 500 21.0 

1400 2316 1320 2240 120 1320 4 × 666 23.0 

1850 2720 1400 2485 120 1400 4 × 1000 27.1 

Tab. 26 Dimensions, boiler support that insulates against structure-borne noise for Logano SK645 and SK745

56 


10.2.3 Flue gas silencer with sealing collar to 

insulate against structure-borne noise 

A substantial proportion of the combustion noise can 

transfer to the building via the flue system. Specially 

matched flue gas silencers can significantly reduce the 

sound level ( Fig. 39). 

The silencer shown, for example ( Fig. 39) achieves an 

attenuation level of approx. 10 dB(A) to 15 dB(A) in the 

flue. The pressure drop caused by the flue gas silencer 

can be disregarded when calculating the flue system. 

The flue gas silencer features a support ( Fig. 39, 

item 3) and a special sealing collar ( Fig. 40, item 1). 

This stepped flue sealing collar and the additional packing 

cord achieve a separation of the structure-borne noise 

between the boiler and the flue system (connection 

piece). 

1 2 

L 4 

D 2 

D 3 

7 

L2 L1 3 4 5 6 

Fig. 39 Flue gas silencer with sealing collar to insulate 

against structure-borne noise 

1 Stepped flue sealing collar 

2 Packing cord 

3 Flue sealing collar ( Fig. 40) 

4 Flue outlet 

5 Connector for checking the flue gas temperature 

6 Boiler casing 

7 Threaded female connection for pipe support 

Dimensions 

at the flue 

gas silencer 

Unit Connection diameter 

DN200 DN250 DN300 DN360 DN400 

D1 mm 200 250 300 360 419 

D2 mm 220 270 320 380 425 

D3 mm 400 600 600 700 660 

L1 mm 1000 650 1090 1240 920 

L2 mm 650 550 850 1000 800 

L3 mm 300 50 160 160 60 

L4 mm 50 50 80 80 60 

Tab. 27 Dimensions, flue gas silencer for 


D 1 

L 3 

6 720 640 417-32.1il 

10.3 Additional accessories 

10.3.1 Welded flange 

Welded flanges to DIN 2633, PN 16 can be used to 

connect commercially available pipes to the boiler flow 

and return. 

10.3.2 Flue sealing collar 

Buderus offers a suitable Flue sealing collar ( Fig. 40) 

to provide a safe connection suitable for positive pressure 

between the boiler flue outlet and the flue connection 

pipe. 

The Flue sealing collar is easy to fit and 

robust in use. DN200, DN250, DN300, 

DN360 and DN400 versions. 

6 720 640 417-34.1il 1 2 3 

Fig. 40 Flue sealing collar (dim. in mm) 

1 Boiler flue outlet 

2 Flue sealing collar 

3 Flue gas silencer or connection pipe 

10.3.3 Cleaning equipment set 

The cleaning equipment set comprises a brush with brush 

handle. It is used to clean the secondary heating surfaces 

and the combustion chamber of the boiler. 


60 

40

11 Flue system 

11.1 General requirements of the flue system 

It is essential that the the flue system is sized correctly to 

safeguard the correct function and safe boiler operation. 

The following recommendations appertaining to the 

implementation of flue systems should guarantee troublefree 

operation of a combustion system. Non-observation 

of these rules can result in substantial operating problems 

during combustion and may even result in explosions. 

These are frequently acoustic disturbances, impairments 

of the combustion stability or excessive vibrations on 

assemblies or their components. Low NOx combustion 

systems are to be viewed as being more sensitive to 

operating faults on account of their combustion control. 

Therefore, engineer and implement the flue system with 

particular care. 

Commonly, the flue system comprises a connection piece 

between the heat source and the vertical flue system itself 

(chimney). 

When sizing and implementing the flue system, comply 

with the following requirements: 

• Flue systems must be sized in accordance with the 

respective national and local regulations and 

applicable standards. General requirements relating to 

flue systems in and on buildings are specified in the 

DIN-EN 1443. The implementation of the flue system 

must comply with local building regulations and the 

DIN V 18160 [Germany]. Apart from building 

regulations, freestanding chimneys are subject to 

DIN 1056, DIN 4133 and DIN-EN 13084-1. For flowtechnical 

determinations appertaining to size, see the 

standards DIN-EN 13384 for flue systems in and on 

buildings, and DIN-EN 13084-1 for freestanding 

chimneys. Observe country-specific regulations. 

• When selecting the material for a flue system, take the 

composition and temperatures of the combustion 

gases into account to prevent damage and 

contamination of the flue parts that are in contact with 

flue gas. 

• Route flue gases as directly as possible to the chimney 

considering the best possible flow characteristics 

(e.g. short and with a gradient and the fewest possible 

deviations). Provide a separate chimney flue for each 

boiler. Take the thermal expansion of the system into 

account. 

• Implement deviations in the connection pieces as 

favourably as possible where flow is concerned by 

using bends or deflectors. Connection pieces with 

several deviations should be avoided, as they would 

have a detrimental effect on air-borne and structureborne 

noise as well as the start-up pressure hammer. 

Prevent sharp-edged joints between rectangular 

connection flanges and the connection pipe. The joint 

Flue system 


11 

angle should not exceed 30°, the same as for any 

reducers/expansions that may be required. 

• Where possible, connection pieces should be joined to 

the chimney in a flow-optimised way (at an angle less 

than 45°). Any terminal pieces at the chimney outlet 

must ensure the free exit of flue gas into the open air. 

• Any condensate must be able to drain freely over the 

entire length, treated in accordance with local 

regulations (e.g. ATV Code of Practice 251) 

[Germany] and drained off in accordance with local 

regulations. 

• Provide cleaning apertures in accordance with local 

regulations (e.g. DIN 18160-1, DIN 18160-5, IVS 

guideline 105), possibly in connection with a local flue 

gas inspector or chimney sweep. 

• The chimney must be separated from the boiler system 

(e.g. with compensators) to break the structure-borne 

noise transfer. 

• Where the flue damper is set into a flue system, a 

safety limit switch “OPEN” must be integrated into the 

boiler control. Combustion must only be able to start 

when the feedback from the limit switch confirms that 

the flue damper is fully open. A temperature drop inside 

the boiler is possible on account of the time it takes the 

actuator to move the damper into position. Implement 

the end position “CLOSED” at the flue damper so that 

the flue damper never closes fully. This prevents 

damage to the integral burner through heat build up. 

As a basis for calculation and for sizing the flue system, 

apply the details in Tab. 28 and Tab. 29. The 

requirements for the flue system and flue gas routing can 

be derived from the results of the calculation and should 

be discussed with the local flue gas inspector [where 

appropriate] prior to constructing the heating system. The 

Logano SK645 and SK745 boilers offer the possibility of 

raising flue temperatures that are too low by approx. 

20 °C to 30 °C. For this, some of the turbulators that are 

accessible from the front after opening the boiler door, 

must be moved.

58 

11 Flue system 

11.2 Flue gas parameters 

Logano Boiler Level Output Rated heat Flue Required Flue gas 

size 

input outlet draught temperature1) Fuel 

Oil Gas 

CO2 Flue gas CO2 Flue gas 

content mass content mass 

flow rate 

flow rate 

[kW] [kW] [kW] [mm] [Pa] [°C] [%] [kg/s] [%] [kg/s] 

120 

2 120 


1) Basis for calculation of the flue system to DIN-EN 13384-1 and DIN-EN 13384-2 

2) 

1 72 

132 

200 0 

198 

13 

0.0560 

10 

0.0562 

3) 80 138 0.0336 0.0337 

190 

2 1902) 1 114 

209 

200 0 

193 

13 

0.0887 

10 

0.0890 

3) 126 138 0.0532 0.0534 

250 

2 2502) 1 150 

274 

250 0 

190 

13 

0.1163 

10 

0.1167 

3) 164 138 0.0698 0.0700 

300 

2 3002) 1 180 

329 

250 0 

188 

13 

0.1396 

10 

0.1402 

3) 360 

2 360 

200 138 0.0838 0.0841 

2) 1 216 

393 

250 0 

188 

13 

0.1668 

10 

0.1674 

3) 236 138 0.1001 0.1005 

420 

2 4202) 1 252 

459 

250 0 

188 

13 

0.1948 

10 

0.1955 

3) 275 138 0.1169 0.1173 

500 

2 5002) 1 300 

546 

300 0 

188 

13 

0.2318 

10 

0.2326 

3) 328 138 0.1391 0.1396 

600 

2 6002) 1 360 

655 

300 0 

188 

13 

0.2780 

10 

0.2790 

3) 393 138 0.1668 0.1674 

Tab. 28 Flue gas parameters Logano SK645 

2) Parameters for the largest value of the rated output range 

3) Parameters for a partial load with 60 % of rated output 

Logano Boiler Level Output Rated heat Flue Required Flue gas 

size 

input outlet draught temperature 1) 

Fuel 

Oil Gas 

CO2 Flue gas CO2 Flue gas 

content mass content mass 

flow rate 

flow rate 

[kW] [kW] [kW] [mm] [Pa] [°C] [%] [kg/s] [%] [kg/s] 

730 

2 730 


1) Basis for calculation of the flue system to DIN-EN 13384-1 and DIN-EN 13384-2 

2) 

1 438 

795 

360 0 

186 

13 

0.3374 

10 

0.3387 

3) 

477 138 0.2025 0.2032 

820 

2 820 2) 

1 492 

893 

360 0 

186 

13 

0.3790 

10 

0.3804 

3) 

536 138 0.2274 0.2283 

1040 

2 1040 2) 

1 624 

1138 

360 0 

186 

13 

0.4830 

10 

0.4848 

3) 

1200 

2 1200 

684 138 0.2898 0.2909 

2) 

1 720 

1313 

360 0 

193 

13 

0.5573 

10 

0.5593 

3) 

789 138 0.3344 0.3356 

1400 

2 1400 2) 

1 840 

1532 

400 0 

193 

13 

0.6503 

10 

0.6526 

3) 

920 138 0.3902 0.3916 

1850 

2 1850 2) 

1 1110 

2024 

400 0 

193 

13 

0.8591 

10 

0.8622 

3) 

1218 138 0.5155 0.5173 

Tab. 29 Flue gas parameters Logano SK745 

2) Parameters for the largest value of the rated output range 

3) Parameters for a partial load with 60 % of rated output 


Index 

B 

Boiler circuit pump ....................................................... 30–32 

Boiler efficiency..................................................................... 13 

Burner 

Burner requirements ....................................................... 15 

Burner selection............................................................... 15 

C 

Chemical additives ............................................................... 23 

Cleaning equipment set ...................................................... 56 

Combustion air...................................................................... 23 

Combustion air supply......................................................... 49 

Control system Logamatic 4000 

Control panel system Logamatic 4411 ...................... 24 

Logamatic 4212............................................................... 24 

Logamatic 4321............................................................... 24 

Logamatic 4322............................................................... 24 

Corrosion................................................................................ 19 

D 

Delivery.................................................................................... 48 

DHW heating......................................................................... 25 

DHW temperature control.................................................. 25 

F 

Fill and top-up water .................................................... 20–23 

Flue gas temperature........................................................... 14 

Flue sealing collar................................................................. 56 

Flue system .................................................................... 57–58 

Fuel .......................................................................................... 19 

G 

Gas shut-off facility............................................................... 49 

H 

Health and Safety at Work Act [Germany]..................... 17 

Heating water routing ............................................................ 6 

Hot gas routing ....................................................................... 6 

Hydraulic connection........................................................... 26 

Hydraulic separation ............................................................ 36 

I 

Installation information......................................................... 48 

Installation room 

Combustion air supply.................................................... 49 

Installation of combustion equipment ......................... 49 

Installed dimensions............................................................. 51 

Index 

L 

Logamatic-Telecontrol system........................................... 24 


Applications ......................................................................... 4 

Burner................................................................................. 15 

Delivery .............................................................................. 48 

Dimensions .................................................................... 7–8 

Equipment level................................................................... 5 

Features and key benefits................................................. 4 

Flue gas parameters ....................................................... 58 

Handling details ............................................................... 50 

Installed dimensions........................................................ 51 

Operating conditions...................................................... 18 

Parameters................................................................ 12–14 

Specification.................................................................. 7–8 

System examples..................................................... 34–47 

Types and output................................................................ 4 


Applications ......................................................................... 4 

Burner................................................................................. 15 

Delivery .............................................................................. 48 

Dimensions .................................................................. 9–11 

Equipment level................................................................... 5 

Features and key benefits................................................. 4 

Flue gas parameters ....................................................... 58 

Handling details ............................................................... 50 

Installed dimensions........................................................ 51 

Operating conditions...................................................... 18 

Parameters................................................................ 12–14 

Specification................................................................ 9–11 

System examples..................................................... 34–47 

Types and output................................................................ 4 

Low loss header.................................................................... 33 

Low water indicator.............................................................. 52 

N 

Noise attenuation 

Boiler supports......................................................... 54–55 

Flue gas silencer with sealing collar ........................... 56 

Requirements ................................................................... 54 

O 

Operating conditions........................................................... 18 

P 

Pressure drop on the water side....................................... 12 

Pressure Equipment Directive (PED)............................... 16 

R 

Regulations ............................................................................ 16 

Return temperature raising facility.................................... 36 


Index 

S 

Safety equipment........................................... 27–29, 52–53 

Arrangement of safety equipment........................ 28–29 

Boiler safety assembly.................................................... 53 

Low water indicator......................................................... 52 

Requirements ................................................................... 27 

Scale formation ..................................................................... 20 

Standby loss .......................................................................... 14 

System example 

Single boiler system........................................................ 36 

System examples.......................................................... 34–47 

Boiler circuit pump .................................................. 30–32 

Boilers Logano S825L ................................................... 36 

Control ............................................................................... 27 

DHW heating.................................................................... 27 

Hydraulic connection...................................................... 26 

Information................................................................. 26–27 

Low loss header............................................................... 33 

W 

Water treatment............................................................ 19–23 

Welded flange....................................................................... 56 

60 


Notes 


Notes 

62 


Notes 


Bosch Thermotechnik GmbH 

Sophienstrasse 30 - 32 

35576 Wetzlar 

www.buderus.com 

6 720 646 816 (10/2010) 

Subject to technical modifications.

Logano SK645/SK745 - Buderus

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