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