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Frequently asked questions about Radiant
Note: Information provided by Watts Radiant,
the primary radiant floor heating system that we offer.
How much should a typical radiant floor heating system cost?
System costs will vary greatly depending on the installation requirements,
control choices, and project size. Simple radiant heat systems in large slabs
in temperate zones cost only slightly more than the alternatives. However, if
you select the many options and features that radiant can offer your home, the
first cost will be higher.
Remember that the principal advantages of radiant are comfort
and lower operating costs. You should review your plans and requirements with
your installing contractor to get a firm price on a turn-key system.
Does a radiant heat system cost less to operate than the alternatives?
Yes they do. The amount of savings will vary depending on the
heat loss, how well the structure is built, how well the building is insulated
and the natural fuel source being used. For the most part radiant floors will
operate anywhere from 25% to 40% more efficiently that other forms of forced air
Are energy saving set-back thermostats desirable on a radiant
floor heat system?
It is not recommended to use a set-back thermostat on a radiant
heat system. Radiant heat systems do not respond as rapidly as a convection type
heating system, mainly because a radiant floor heat system uses the mass of the
building to store energy and to provide a more even heat.
What type of maintenance is required for my radiant heating
Most maintenance items center on the pumps and boilers. For the
most part, the pumps used today are maintenance free. They use water to lubricate
the bearings, which allow for more quiet, efficient life span. In general, these
pumps have an estimated life span of 10 years. Most boiler installers will offer
a yearly maintenance package, which includes cleaning and general up-keep. Different
boiler types will require different maintenance.
What type of glycol should I use in my snow melt system?
An inhibited Propylene Glycol solution should be used. Make sure
the glycol used is rated for hydronic radiant heating systems and not for automotive
engines. Hydronic glycols are formulated differently for the metals seen in boilers,
pumps and other system components.
How often should I check my glycol system?
Glycol systems should be checked at least once a year to ensure
the system pH levels have not dropped below recommended levels. Glycol in general
is acidic. The inhibitors that are added to them help neutralize the system pH,
and help protect the system components. As the system ages, the inhibitors break
down, causing the system pH to drop. At this point more inhibitors should be added
to the radiant floor heating and snow melt systems. The system will reach a point
where it will require a complete flush and re-fill. This is usually around 5-7
years, but will depend on the glycol used.
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 bests suites the needs of the
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.
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
Radiant heating works in just the opposite way. Since a radiant
heat system stores its energy in the floor, all of the room's warmth is kept right
where it needs to be, on the floor where you are. The ceiling in a radiant floor
system is always much cooler than the floor area, just the way you would want
it. This cooler ceiling temperature means less energy is being wasted to the outside.
Less waste means higher efficiency.
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.
Why do we need to be heated?
Actually, we don't need to be heated, not in the same sense one
might think. Since we are living beings, we actually produce our own energy, or
heat, by consuming food (calories). Movements and other activities consume these
calories, and a by product of this consumption is heat. Our bodies operate at
around 98.6 Degrees F. By controlling the temperature of our surroundings, such
as chairs, walls, windows, etc., we will have more control over our own body's
heat loss, which will make us feel warmer and enhance comfort.
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.
Does a radiant house take a long time to heat up from a cold
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.
Does a radiant heating system have any impact on air circulation
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.
What type of floor construction should I use?
Any type of floor construction can be used with a radiant heat
system. The most common will be a slab on grade, or a frame floor. Some variations
of these may include a thin slab over a frame floor or a Sandwich application.
The important thing to remember is to inform the radiant designer of the exact
construction of the floor. There will be design variations between a frame floor
project and a slab on grade. Keep in mind, it is better to design the building
for what is required structurally and let the radiant system be designed around
the construction details.
What type of floor coverings can be used over a radiant heat
Most floor coverings can be used over a hydronic heating system,
keeping in mind that the system is designed for that particular covering.
Tile is the most efficient, since it is the most conductive. Hardwoods
come next, and then carpet and pad. Even vinyl or linoleum can be used. Typically
the only design variance between these three common floor coverings, is supply
I've heard hardwood floors should not be used. Why is that?
Hardwood floors can be used over a hydronic heating system if
extra time and care is used during the installation process. Wood floors are what
we call hydroscopic. That means the wood reacts to water, in much the same way
a sponge does. If the wood is dry and goes into a wet environment, then the wood
floor will adsorb moister and expand. Likewise, if the wood is too "wet" and is
installed into a dry environment, it will dry and shrink.
Wood floors continuously move, just like the door jams in your
home. In the summer they expand due to the increased humidity in the air and become
harder to shut And, in the winter the humidity is typically lower, and the doors
shrink, becoming easier to close.
Wood floors will also experience this seasonal change in dimensions.
However, there are some "tricks to the trade" that will help minimize these swings.
Use a wood that is kiln dried. This helps to ensure the wood's
moisture content is the same on the inside as it is on the outside.
Try to use a wood that is no wider than 3" to 3.5" in width. The
narrower the strip, the less movement it can induce.
A quarter-sawn wood is better than a plane-sawn wood. Plane sawn
woods tend to "grow" or expand in width, while a quarter-sawn wood will tend to
expand more in thickness. This helps reduce visual cracking and gapping.
The wood should be around 7% - 10% in moisture content. This may
require an acclimation period in order for the wood to reach this level. Sometimes,
it is best to have the radiant system installed before the wood. This will help
accelerate the acclimation process.
The wood floor should not be higher than 4% in moisture content
than the floor it is being installed onto. This will allow for the subfloor and
hardwood floor to move and react as a single unit. Otherwise, moisture maybe able
to travel from layer to layer.
What about the nails used with a hardwood floor?
Typically, hardwood installers use one nail that will allow for
the most use in the most variety of applications. However, this single nail tends
to penetrate the lower surface of the subfloor, placing the radiant heat tubing
in jeopardy. To eliminate this threat, ask the hardwood installers to use a shorter
nail, one that will not penetrate the subfloor. And, if possible, ask them to
try to keep the nails around the joists below. This way if there is some penetration,
it will more likely go into the joist and not the tubing. As with any radiant
heat installation it is a good idea to visually inspect the tubing after the wood
floor is down, along with the factory recommended pressure test.
Is there anything in my floor that can cause problems?
In new construction there really isn't much that can is used that
can cause a problem with a radiant heat system. If a vinyl floor is used, make
sure the adhesive used can withstand elevated temperatures.
However, in a remodel, one thing that can be problematic is the
use of tarpaper. This was used as a slip-sheet for hardwood floors to reduce squeeks
and to act as a vapor barrier. Tarpaper can "off-gas" when heated up, causing
an unpleasant odor to filter into the home. With today's construction techniques,
rosin paper is used instead of tarpaper, which removes the off-gassing problem.
How many zones can I have with my radiant heat system?
A hydronic heating can be designed with as many or as few zones
as desired. Some systems will have one zone per floor, while others will have
each individual room a zone. Keep in mind the more zones there are, generally
the higher the radiant heat system cost.
I'm remodeling my garage, do I have to install a boiler?
Heat sources are chosen based on the water temperatures required
and the total heat load needed for the space. For most full home hydronic heating
systems a boiler will be used, but in some cases, such as a single room addition,
a dedicated water heater may be used. This will be based on local code allowances
and other design considerations.
If a water heater is used, it is not recommended that his same
unit be used to supply the domestic hot water needs. The radiant fluid needs to
be isolated from the potable drinking water.
What is the best way to control my radiant heat system?
Controls are chosen mainly on how the homeowner/project owner
wants their system to respond to changes in outside conditions and on operational
ease. Most systems will use a type of relay control with standard thermostats.
More advanced systems will use outdoor sensors to anticipate climate changes.
These systems are called outdoor reset and they tend to operate more efficiently,
but they do cost a bit more.
Who should I have install my radiant system?
There are professional installers in most areas of the United
States and Canada that specialize in radiant systems. But, any professional building
or plumbing person can install a radiant system.
Can I install part of the system myself?
It is really up to the local code to dictate whether an installer
needs to be licensed. In some areas the general contractor will allow homeowners
to install the tubing while they supervise the work. In most areas a licensed
installer is required to install the heat source, especially if a boiler is being
used. Watts Radiant recommends a professional installer be consulted or used to
install the mechanical package used to control the radiant heat system.
How is heat transferred?
Heat is transferred from on location, or body, to another by three
basic modes. These modes are Convection, Conduction and Radiant Heat.
One basic rule to all three modes is this: heat does not rise,
hot air rises. Heat moves from a hot source to a cold source. Think of a hot air
balloon. It floats because the hot air inside is less dense than the cool air
outside. This literally causes the balloon to float in much the same way a boat
floats on water.
Another way to think of this is to imagine a metal skillet placed
on a stove burner. When the burner is turned on the handle is still cool to the
touch, but as the bottom of the pan warms, the heat moves from this now warm source,
to the cooler outer edges. Eventually the handle will become too hot to handle
and a cooking mitten will be required to handle the skillet.
Explain the types of Heat Transfer
Convective heat transfer is what most of us are familiar with.
This is how our forced air heating system or our baseboard system transfers energy
(heat) to a space. Air moves over a heating element, becomes warmer and expands
into the space. In a forced air environment, most of the hot air is at the ceiling,
much the same way the hot air balloon rises, so will the warm air in a room heated
with forced air. Convective heat transfer is the least efficient means to transfer
Conductive heat transfer refers to two surfaces touching each
other. Imagine a metal pan on the stove. If your hand is positioned an inch above
the hot handle, you really won't feel much from the handle, and you can keep your
hand there as long as you wish. But, when the handle is touched, your hand instantly
begins to feel hot. This is conductive heat transfer. The pot is giving off the
energy (heat) in the handle to your hand in a very fast, efficient manner. Conduction
is one of the more efficient modes of heat transfer.
Radiant heat transfer is the best because it isn't slowed down
by air. Radiant energy is only felt when the energy wave strikes another surface.
This means the surrounding surfaces all reach set temperature. By enclosing your
body by warm surfaces, we can better control how our bodies lose heat. Radiant
floor heat means better comfort with higher efficiency.
What type of piping should I use?
Watts Radiant offers two different types of radiant tubing options,
each has its own unique qualities. Watts Radiant's Onix tubing is the most diversified
product in the market today. It is the only product that can be installed under
a frame floor with no additional accessories required (no heat transfer plates,
no special clips). Since the Onix does not expand or contract with temperature
changes, it is the quietest system around.
Watts Radiant also offers a Pex line (cross-linked Polyethylene).
This product is typically used in slab or thin-slab applications, but can also
be installed under a frame floor with the use of heat transfer plates or clips.
As long as the tubing chosen is installed properly and per the
manufacture's recommendations, the radiant heat system will perform beyond expectations.
Are baseboard "radiators" really radiant heat?
Baseboards are actually convectors. They heat the air by creating
a temperature differential across the fins. This temperature difference "pulls"
the cooler air across the heated fins. The warmed air then rises, adding to the
Radiators operate in a similar fashion as a baseboard unit, but
with one difference. Because radiators have a much higher mass and tend to have
more exposed heated surface, they do provide a certain amount of radiant heat
to a space.