CMX 2004 - Plumbing & HVAC

Hot Water Heating
The perfect way to heat
a garage or workshop
By Roy Collver
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HIGH TEMPERATURE HEAT SOURCE
INJECTION MIXING PUMP
RADIANT FLOOR - STAGE ONE HEAT
HYDRONIC UNIT HEATER - STAGE TWO HEAT
UNIT HEATER ZONE VALVE
Experience is a
great teacher. I
have listened to
many complaints
over the years from
people who wanted
the ultimate in hydronic
luxury and
paid a big price to get it – only to be disappointed
by the end result. I’m not
talking about hydronic towel warmers,
radiant bathroom warm floors or great
room panel rads – I’m talking about
something far more important – the
heated garage/workshop. (Now you’re
talking! – ed)
You can tweak the interest of many
consumers with granite counter tops,
hot tubs, theater rooms and other such
trivial luxuries for their new house, but
one of the most appealing upgrades you
can offer is a heated garage where they
can keep not only their precious classic
car, but keep themselves comfortable
while they pursue their favorite hobby.
The decision to heat a garage is a logical
one when you have already decided
to put in hydronic heating. The addition
really adds minimal cost to the
heating system and is easily done. The
trick is to do it properly and avoid some
of the most common mistakes I have
seen over the years:
Common complaint No. 1: Water
collects on the floor and the air
becomes laden with humidity.
This year, we have had a pretty ugly
winter all across this fine land. In years
like this the complaints are numerous as
people bring their snow encrusted cars
cost of fuel these days, it is common to
set the temperature in the garage down
low (usually 5°C to 10°C), and turn it
up to a more comfortable temperature
only when it is being used. There are
two very important design details that
can make this type of operation work
very well with a radiant slab-on-grade
heating system.
First of all, make sure the slab is insulated
beneath the concrete so you aren’t
sending all of your heat straight down
to China. There is some controversy
over the benefits of insulating under a
slab where dry soil conditions exist,
with some people claiming that once
such a slab is up to temperature, the
underlying soil acts as a big heat sink
and stabilizes the temperature of the
floor. These people may have a point
with some specific slab heating applications,
but not in buildings that are subject
to rapidly fluctuating outdoor temperatures
or systems where setback is
regularly used.
So definitely insulate, but even when
you do, it can take quite a while for a
garage to heat up even a few degrees
and you run the risk of overheating the
space. Temperature swings occur because
there is always a lag between the
time a thermostat is satisfied with the
air temperature and the time the floor
stops pumping heat into the room. A
concrete slab is still a pretty big heat
sink, even if it is properly insulated –
which brings us to our second detail.
Use a two-stage thermostat to operate
a high output, low-mass heating unit to
boost your air temperature in conjunction
with your radiant slab. Some examples
are: Fan coil type heaters (such as
hydronic unit heaters, forced-flow heaters
or air handlers), fin-tube convectors
with lots of element, or panel radiators
with lots of surface area. Each specific
application will favour a different type of
‘booster’ heat terminal unit.
Some suspended unit heaters are no
bigger than a breadbox, but put out
many thousands of Btus and can bring a
large garage up through 10°C in a matter
of minutes. However, you would not
want to use such a heater in a garage that
also doubled as a woodworking shop,
due to the fire hazard with sawdust.
Panel radiators might be a better
choice (no air blowing around and no
coils to fill up with dust). Keep in mind
that you may have two different water
temperature requirements for this
approach, mixed water for the slab, and
high temperature water for the low
mass heater. If you design the low mass
heater for lower water temperatures you
might get away with using a single
mixed water temperature for both.
into their nicely heated garages and
watch helplessly as the snow and frozen
mud plops off onto the floor and forms
a rapidly expanding pool that soaks into
the drywall, rusts any metal object on
the floor (like that brand new table saw)
and freezes the overhead door shut.
When the water does evaporate, it
fills the air with humidity which
streams down and frosts over the windows
and creates a clammy, mold-inducing
atmosphere sure to cause no end
of trouble down the road.
A few simple design details can help
you avoid all of this grief and give your
customer the system they thought they
were going to get when they hired you.
First of all, put in a floor drain and
properly slope the garage floor towards it
so that excess moisture can drain away.
Make sure you use a good quality drain
that can be cleaned easily of all of the
sand, gravel and other flotsam and jetsam
that is brought in by your average car.
Second, install a good exhaust fan (I
have seen some people go as far as to
put in an HRV) and operate it with a
de-humidistat so you can chase that
moist air outside. These two details are
hugely important and, in my opinion,
are an absolute necessity in order to
make a cozy, clean work environment.
Common complaint No. 2: Many
garages in newer homes use a radiant
slab as the heat source. This is a particularly
elegant way to heat such a space,
since it will help with problem No. 1
(above) by speeding the evaporation of
excess water on the floor, as well as providing
a quiet and extremely comfort-
Real life operation
This may all seem a little extravagant
for a mere garage, but let’s look at how
this perfect garage system works in
real life:
You pull into your driveway after a
hard day and you are looking forward to a
good dinner and a couple of quiet hours
to yourself afterwards: restoring your latest
baby – a vintage Norton Commando
able working space.
you picked up last summer. (Sounds like
1 WARM WATER HEAT SOURCE
2 RADIANT FLOOR - STAGE ONE HEAT
The problem is that it
pure Heaven, but the wife might have
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3 HYDRONIC UNIT HEATER - STAGE TWO HEAT
takes too long to
something to say about it! – ed)
4 UNIT HEATER ZONE VALVE
bring the garage up to
You pop the garage door and the air
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a comfortable working
temperature from
drops from plus 10°C to minus 10°C as
temperature in your garage immediately
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setback.
it fills with cold outside air. Your twostage
thermostat reacts immediately and
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Most homeowners
only use their
brings both your radiant slab and your
garage/workshop on
18,000 Btuh unit heater on full blast.
- TWO STAGE GARAGE/WORKSHOP HEATING WITH A WARM WATER HEAT SOURCE (CONDENSING BOILER,
HEAT PUMP, ELECTRIC BOILER, ETC.) - THE BOILER SUPPLIES WARM WATER TO BOTH THE RADIANT FLOOR
SLAB AND THE UNIT HEATER AND THIS STARTS TO GET QUITE TRICKY -
weekends or after
After the door closes, the room immediately
starts to warm up. You crank
THE UNIT HEATER MUST BE OVER-SIZED IN ORDER TO PROVIDE SUFFICIENT HEAT AT THE LOWER WATER
TEMPERATURES TYPICAL OF A RADIANT SLAB HEATING SYSTEM AND IN ADDITION, THE WATER TEMPERATURE work, and then for
TO THE SLAB MAY HAVE TO BE ELEVATED MORE THAN NORMAL TO MAKE THE UNIT HEATER EFFECTIVE
only a few hours at a
the thermostat up to 20°C as you go into
On the other hand, this system works well too.
time. With the rising
the house for dinner. All of the snow and
slush drops off of the underside of your
car and quickly melts on the warm floor.
The water runs down the floor drain or
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rises, the de-humidistat turns on your
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heat recovery ventilator and exhausts
Flow Rates from 4 to 75 GPM
the moisture to the outside.
By the time you’ve had dinner and
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watched the evening news, the garage is
up to 20°C, the floor is dry and the unit
Bolt-on Extensions available in two
configurations for flexibility
heater has kicked off leaving the radiant
floor to quietly and gently warm the
room. You go out into your warm garage
and start stripping down the motor-
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cycle’s engine while your Husband finishes
up the dishes. (Yikes!)
MADE IN
Floor Drains Parking Area Drains Trench Drains Roof Drains Special Purpose Drains Drain Pro CANADA
Floor Sinks Grease Interceptors Oil Interceptors Solids Interceptors Hydrants Fixture Carriers Cleanouts
Perfect.
Circle Number 119 for More Information
20 Plumbing & HVAC Product News – March/April 2004 www.plumbingandhvac.ca
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- TWO STAGE GARAGE/WORKSHOP HEATING WITH A HIGH TEMPERATURE HEAT SOURCE -
THE MIXING SYSTEM SUPPLIES WARM WATER TO THE RADIANT FLOOR SLAB AND THE UNIT HEATER
IS SUPPLIED WITH HIGH TEMPERATURE WATER DIRECTLY FROM THE BOILER LOOP
There are many ways to pipe garage heating. This is one good way, says Roy.
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