Hardwood Flooring Over Radiant Heating
 Radiant heating is a growing source of heating in North America,
both in residential and commercial installations. Consequently, it's
important for installers to understand how radiant heating works
with hardwood flooring installations.
Radiant heating does not heat air directly as do more conventional
forms of heating, such as baseboard convectors or forced air
circulation. Radiant heat is "omni-directional." Unlike warm air,
which tends to rise, radiant energy tends to travel in all
directions. A large area of mild surface temperatures, such as a
warm floor, is capable of transferring as much heat as a small
surface area, such as a steam radiator, at high surface
temperatures.
Radiant heat beneath wood flooring involves tubing in concrete, or
tubing under plywood subfloors.
The most important factor in a successful wood flooring installation
over radiant heat is a dry slab and a dry subfloor. The only sure
way to dry a slab and sub floor system is to turn on the radiant
heating system before installing the hardwood flooring. If this
isn't done, moisture left in the slab will enter the wood flooring
as soon as the heat is turned on. The result is floors that will
expand, contract, shrink, crack, cup and bow excessively. If the
heat
can't be turned on, then everyone involved - down to the homeowner -
should understand and accept the compromises that will appear down
the road.
Opinions on the amount of time required vary widely. Some say the
heating system should be turned on at least 72 hours before
installation, with a preferred time of five to six days. That
assumes that the slab has been in place for at least 60 days. (See
'Testing concrete".) If the slab is relatively new, the
recommendation is to have the heating system turned on for 30 to 60 days before installing wood
floors. As always, follow the recommendations of your wood flooring
manufacturer.
Wood dries rapidly when the heat is first turned on. It dries to a
lower moisture content toward the end of the heating season. When
the radiant heat is turned off, moisture once again starts to
seep into the wood subfloor and radiant slab. Abruptly turning on
the radiant heat in the fall will subject wood flooring to rapid and
easily noticed movement: Evidence f this movement will be cupping or
crowning of the boards. Finally, shrinkage cracks will appear
between individual floor boards. Alternatively, gradually turning
the heat on before the first really cool
ay will begin the seasonal movement more gradually. Thus, the
movement of the floor will be much less noticeable. As always,
humidity controls can help offset flooring expansion and
contraction.
Not all species of wood are good candidates for an installation over
radiant heating. It's best to follow the
manufacturer's recommendation for a species' suitability over
radiant heat. When possible, choose a species that is known for its
stability. Quartersawn or rift-sawn flooring is preferable to
plainsawn in the search for stability. Strip flooring is also a
better choice than plank flooring, because narrow boards expand and
contract less than wide boards do. Using narrow boards also means
there are more seams in a floor to take up movement. Because of its
dimensional stability, laminated flooring is another good choice.
Radiant heating systems are currently designed to run cooler than
they did years ago, although water supplied to the systems generally
range from 90 degrees to 140 degrees. In years past, when water
temperatures exceeded 140 degrees, wood fibers were repeatedly
traumatized, causing stress fractures, gaps and twisting. Repeated
heating and cooling also broke down the adhesive that bonded the
hardwood to the slab. (see installation diagrams)
But today, a set of thermostat controls can help avoid those
problems. It is recommended to have three thermostats - one to
control the tubing water supply temperature; one to control the room
temperature with different zone controls; and one for outside the
house. This three-thermostat system is kindest to wood flooring,
because it moderates the floor temperature. People tend to crank up
the heat when they're cold. but with three thermostats, the system
adapts itself to conditions both inside and out. The outside
thermostat gears up the system for the arrival of colder weather,
and a thermostat adjusting the control water temperature on the
tubing will keep the temperature at the homeowner's comfort level.
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Fast Facts > Learn More > Related >
Choosing A Wood Floor Contractor
Domestic Species
Exotic Imported Species
Finishing Wood Floors
History of Wood Floors
Installing Wood Floors
Problems & Cures
Styles & Types of Hardwood Floors
Technical Help
Types of Finishes
Wood Cuts & Grades
Wood Floor TV
Wood & Water
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