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250
HEAT LOSS INFORMATION
THICKNESS OF INSULATION, INCHES
WATTS PER SQUARE INCH
8
7
6
5
4
3
2
40
30
20
10
4” and larger
3” pipe
2” pipe
1” pipe
1
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
CORRECTION FACTOR
CORRECTION FACTORS FOR INSULATED PIPELINE HEAT LOSSES
where more than 1 inch of insulation is applied to pipe lines, obtain the heat
loss from HEAT LOSSES FROM INSULATED PIPE LINES and multiply by the
appropriate factor from the above curves to determine the proper heat loss.
SHEATH
TEMP
1000˚F
SHEATH
TEMP
600˚F
SHEATH TEMP
1400˚F
SHEATH
TEMP
1200˚F
200 400 600 800 1000 1200 1400
TEMPERATURE OF AIR ˚F
ALLOWABLE WATT DENSITY ON TUBULAR UNITS OPERATING AT 800˚F TO 1400˚F
Sheath temperature for various temperatures in distributed air velocity of 16 fps
NOTE:
Varying circumstances can e�ect the accuracy of
any �gures obtained from these charts. They should
be used as a guide only in determining
requirements for electrical heating elements.
190 Detroit Street • Cary, Illinois 60013 • Phone: 847-639-5600 • Fax: 847-639-2199 • Web: www.durexindustries.com • TOLL FREE: 800-762-3468
WATTS PER SQUARE INCH
KILOWATTS
50
40
30
20
10
170
150
130
110
90
70
50
30
10
0
10 FPS
9 FPS
4 FPS
200 400 600 800 1000 1200 1400
SHEATH TEMPERATURE ˚F
SHEATH TEMPERATURE OF TUBULAR UNITS
at various watt densities in free or forced air at 80˚F
600˚F RISE
550˚F RISE
500˚F RISE
450˚F RISE
400˚F RISE
350˚F RISE
300˚F RISE
250˚F RISE
200˚F RISE
1 FPS
150˚F RISE
100˚F RISE
75˚F RISE
50˚F RISE
1 3 5 7 9 11
HUNDRED CUBIC FEET OF AIR PER MINUTE
HEAT REQUIREMENTS FOR AIR (.08 LBS./CU. FT
weight and speci�c heat .237 Btu/Lbs./˚F
STILL AIR