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PEX Radiant Heat FAQ's
Hydronic Radiant Floor Heat and Electric Radiant Heat Systems
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How is radiant heat different from the baseboard heat that I have now?
- Convection
With baseboard, 80% of the heat is transferred by convection and only 20% by radiation.
This means that if you place a pair of frozen boots in the middle of your mud room you have
to crank the heat up to 74° to get the boots thawed. Both forced-air and hot water
baseboard are convective and the air is warmer the higher in the room you go.
- Radiant
With a radiant system you set the thermostat at 65° and the boots are radiated from the
floor up. This is accomplished by radiation or emission of energy of a wave length not visible
to the human eye. Best example would be warmth felt from the sun. In a convectively heated
room the thermostat must be set to 74° to keep feet warm.
In a radiant floor heated room the thermostat can be set at 65 degrees. Feet are conductively
satisfied with the 70-72° floor. Being able to set a lower thermostat results in a
lower bill at the end of the month!
More comfortable, quieter, better air quality all for a lower bill each month.
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What are the different ways to install radiant heat?
- Slab
- Thermal Board
- Under Floor
The radiant staple is another way to incorporate an existing space with radiant heat. The
tubing can be stapled up to the bottom of the existing subfloor using heat dissipation plates.
These plates allow for the heat to spread more evenly amongst the bottom of the floor providing
better radiation.
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I've heard that older radiant heating systems made the floors too hot. True?
Yes, this is a true statement to some degree. In the past, radiant heating systems were designed
and installed in much the same way as a conventional baseboard system. High temperatures and
simple controls were used to control the radiant heating system. These high temperatures
were in fact too high from a comfort standpoint. The higher the water temperature in the floor,
the higher the floor surface temperature will become. For all systems a maximum floor
temperature of 85°F is maintained to ensure comfort. In these older systems, the floor
temperature could actually exceed this limit, causing the floor to feel uncomfortable.
Today there are endless arrays of controls and piping methods to ensure this does not
happen. Lower water temperatures are maintained to prevent over heating. Indoor/outdoor reset
systems are used to help predict heating needs and to increase response times. Radiant heating
technology is becoming more and more advanced everyday.
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Does a radiant house take a long time to heat up from a cold start?
Most radiant floor heat systems take about a day to come up to full temperature. The reason
for this is due to how the radiant heating system stores energy. Before a radiant floor can
emit energy (heat) into a space, it first has to raise the floor temperature. Depending on the
floor construction and the initial floor temperature, this start up time may be anywhere from
a few hours to a few days. Slab on grade floors will see the largest start up time, mainly
because they will have the highest mass value.
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Does a radiant heating system have any impact on air circulation or cleanliness?
Yes. Since the air is not carrying the heating, and is not being forced to move through the house,
less dust and mold is being distributed. This helps to keep allergies and other ailments
to a minimum.
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Can I use any kind of fuel source in my radiant heating system?
Any natural resource can be used to fire the heat source - natural gas, propane, electric,
wood, geo-thermal, etc. It does not matter what the heat source is, as long as it can
provide the necessary btu's (energy) at the required design temperatures. There will be a
variance between heat sources based on efficiency, response, cost and capacity. Choose the
one that best suites the needs of the heating system.
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Can I air condition my home with a radiant floor heating system?
It is not advised to try to "air condition" a space with a radiant heating system. In theory
a radiant floor can be used to cool a space. In order to lower the internal temperature of a
space, the cooling surface has to drop in temperature. This lower temperature "pulls" the heat
from the air and is then carried away through the liquid in the tubing below the floor.
There are two main problems with this application. First, the lowered floor temperature needs
to be below the room's dew point to effectively remove energy (heat) from a space. This
lowered temperature will cause a layer of condensation to form on the floor surface, which
may cause damage to a floor covering, not to mention creating a safety hazard. The second
main reason is comfort. Our goal with any environmental control system is to maintain a higher
level of comfort than what could be seen naturally. Part of this comfort level is dictated
by touch. If the surface we stand on is too cool, which would be the case in a radiantly
cooled home, our comfort level is severally compromised.
One note should be added here: There are systems in existence that claim to do radiant floor
cooling. In fact, most of these systems are coupled with some sort of air handler to prevent
the floor from condensing.
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I'm planning a large house with high ceilings and lots of windows. Is radiant floor heating practical?
High ceilings and "lots of windows" are one of the main reasons why radiant heat is chosen as a
building heating system. Since hot air rises, in a forced air heating system all of the nice,
usable heat is first sent to the ceiling. This may be anywhere from 10 to 20 feet up. By the
time this air makes its way to your level, about 6-ft. off the ground, it has lost most of its
energy and has started to get pushed down by the other hot air entering the room. If this air is
cooler than when it entered, where did all of its heat go? Right out the ceiling.
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Can my radiant system also melt snow and ice?
Snow melt systems are becoming more and more popular, especially in areas where nature
conservation is important. Snow melt systems eliminate all of the other necessary chemicals
and pollutants used today to keep areas free of ice and snow. No more salt to track indoors.
No more uneven melting. Streams and rivers no longer get polluted with unnecessary additives.
Snow melt systems also protect your investment. Slabs last longer. Salt and other chemical
additives will begin to break down the surface of a concrete slab over the years. For brick
paver applications, snowmelt systems provide a certain amount of physical protection. Keep
dangerous snow plows away and retain the beauty of your investment.
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Floor Covering
Any floor covering can be used with a radiant heat system. The key is to ensure the radiant
design uses the correct floor covering. Different floor coverings will have different
R-values (their ability to restrict energy transfer). Carpet is more restrictive than tile,
but can still be used. The difference is usually a slightly higher supply water temperature.
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Tile
One of the main concerns with regard to tile is cracking. There are three main reasons why
tile cracks: deflection, moisture and crack migration from the substrate. Some simple
guidelines can be followed to minimize these concerns.
- Always install the substrate per TCA (Tile Council of America). This may include a cement
backerboard, thick set, double layer of plywood or a thin slab.
- Do not run the radiant heat system until the substrate has cured. A minimum of 7 days is
required, 15 days is better and 28 days is ideal.
- Install a crack suppressant membrane. This will help retard any crack progress that
may originate in the substrate.
www.tileusa.com
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Hardwoods
Wood is what is referred to as being hydroscopic, or basically it will act like a sponge.
If the wood is installed dry, it will absorb moisture and expand. The following guidelines
will help eliminate errors associated with hardwood floor installations:
- Use strips, not planks. Ideal width is 3" to 3.5" in width.
- Use kiln dried wood.
- Make sure the wood is between 7% and 10% moisture content when it is installed.
- Make sure the support floor below the wood is no higher than 4% moisture content than the hardwood.
- Quarter sawn wood will respond better than a plain sawn wood.
- Try to keep the room's relative humidity between 35% and 50%.
www.hardwoodcouncil.com
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Carpet
There are various reports that carpet can not be used over a radiant system. The truth to the
matter is that carpet works just fine, if the system is designed with carpet in mind. There
is a greater range for error with carpet, depending on the combination of pad and carpet used.
An ideal R-value for a carpet and pad is around 2.0 or less.
www.carpet-rug.com
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Hydronic Tubes vs. Electric Cable
In a hydronic system, water is heated by a boiler or water heater and circulated through
flexible tubes buried in the floor. The floor absorbs this energy, then gives it off as
radiant heat, which warms people and objects in the room.
An
electric radiant floor system works the same way, but instead of tubes, electric heating elements
warm the floor. Electric radiant systems are easier and less expensive to install than their hydronic
counterparts. They're also less expensive to zone. They can be used to heat a whole house or to
provide spot comfort in kitchens and bathrooms.
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