How does radiant heating work?
Unlike conventional forced air heating systems, radiant heating does not heat air directly. Warm air rises and much is lost, making forced air heating less energy efficient. Radiant heating works by transferring heat to objects, so when placed beneath wood flooring it heats the floor. Since less heat is lost through the air, radiant heating is more energy efficient than forced air heating systems.
Electric radiant heating systems use thin electric mats that work much like electric blankets. They are often used to heat small rooms like bathrooms and kitchens. For larger rooms, a hydronic radiant heating system is usually used. This involves tubing in a concrete slab, or tubing under plywood subfloors. Heated water is pumped through the tubing network where it releases its heat energy into the floor.
Installation guidelines
Dry subfloor
The most important factor in successfully installing hardwood floors over radiant heating is a dry subfloor. The only sure way to do this is to turn on the radiant heating system before installing the wood flooring. If this isn't done, moisture left in the subfloor will enter the wood flooring as soon as the heat is turned on. This will result in floors that expand, contract, crack and warp excessively. A high quality vapor retardant should also be installed over the subfloor to protect the hardwood floor from moisture.
Concrete floor
When installing over a concrete slab, the radiant heating system should ideally be turned on for several weeks before the hardwood flooring is installed. Also, the hardwood must be stored in the house for 7 to 10 days before installation so it can acclimate.
Excessive moisture?
To check for the presence of excessive moisture in the slab, tape a 4x4 foot section of polyethylene plastic sheeting to the slab and turn on the heat. If moisture appears under the plastic, heat the slab for another 24 hours, repeating the test until no moisture is visible.
Which wood for radiant-heat flooring?
It is best to choose a wood species that is known for its stability. American hardwoods such as cherry, oak, ash, maple, hickory and walnut are good choices for radiant-heat flooring. Parquet floors are an excellent choice in radiant heat applications. Laminated flooring is another good choice because of its dimensional stability.
What kind of board width?
It is best to use narrow boards, no wider than 3 inches. They will better accommodate the wood’s expansion and contraction across a floor because there are more seams in a floor to take up movement. Narrow boards also expand and contract less than wide boards do. The wider the board, the greater the potential for gaps between the boards when they contract with seasonal changes in temperature and humidity. If you must use planks wider than 3 inches, consider using quarter-sawn wood for enhanced dimensional stability.
Temperature control
Whilst temperature will not harm the wood, it does affect its moisture content. With the heat source is directly beneath the flooring, it can gain moisture or dry out faster than flooring in a home with a conventional heating system. It is important that the temperature variations are smooth and gentle, and that the surface temperature of the wood floor does not exceed 85 degrees. This is easily achieved with the following climate controls:
• mechanical humidity control – this keeps the relative humidity at an even level so the moisture content of the floor will remain stable.
• heat transfer point control – monitors the wood floor temperature to prevent overheating.
• exterior thermostat – protects the perimeter of the system from condensation absorption during rapid temperature changes.
Radiant heating is not only more economical in the long run, it is also a good choice for allergy sufferers who wish to avoid the dust blown about by forced air heating systems. Installing hardwood floors over radiant heating will enhance the value and aesthetics of your home and provide a warm, cosy and comfortable environment during the cold winter months.
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