Posted on the 101
It is known that not all wood species are appropriate for radiant heat (RH) installations. Therefore if you prefer to use solid wood for radiant heat applications choose a species known for its *stability. Here in descending order are the best choices for in-floor heating as recommended by the National Wood Flooring Association (NWFA)
Floating wood floors and laminates - Most recommended because these types of floorings are not attached to the subfloor therefore free to move as a total unit to better accommodate for environmental (moisture and temperature) fluctuations
Engineered flooring –Works well over radiant heat because its unique plywood construction creates greater stability as each wood layer is positioned perpendicular to the other thereby resisting movement from environmental fluctuations. (Depending on selection can be nailed, glued or floated to the subflooring)
Solid wood - quarter-sawn or rift-sawn – This cut or style of flooring is most preferable to because it tends to expand more upwards in the direction of the grain with less side to side movement common with plain-sawn cut flooring. In addition, quarter-sawn solid flooring reduces the likelihood of gapping and board edge cupping due to environmental fluctuations.
Solid wood- strip flooring, boards 3” wide and less – A better choice than plank or wider flooring because narrow boards seams will allow for any excessive board movement and will expand and contract less than wide boards. As a general rule, the wider the boards the wider gaps can be.
When choosing to use solid boards or planks wider than 3" make sure the board moisture content is dry to around 6-9% before and maintained well after installation. For any wood application over radiant heat, the newly installed system should be operating some two weeks prior to the floor installation, this precaution helps to further dry out any unknown pockets of trapped moisture. Because of the wide array of systems on the market, each with its own features, please consult with your radiant heat provider for recommended installation methods. Hydronic systems must include in-floor temperature sensors and an outdoor thermostat that allows the system to adjust the water temperature according to anticipated heat loss. Radiant heat contributes to the drying out of all woods. Use of a humidification system may be required to maintain the proper humidity level. The indoor relative humidity must be maintained between 30-50% year round. Failure to do so can result in edge cupping, squeaking delamination, splintering, or face checking. Avoid shock to the floor, Before installation, run new systems to dissipate hidden or trapped moisture. During installation, reduce thermostat to 65°F. 48 hours after installation, slowly raise the temperature of the heating system to its preferred operating level over a period of 5 days. The surface temperature of the subfloor must never exceed 85°F in any location. The temperature setting must always remain within 15°F of normal operating level, and should never be turned completely off. Excessive heat, rapid heating, and/or failure to maintain humidity levels between 30% and 50% is likely to result in cracking, cupping, squeaking and other forms of floor issues. Slight surface splits (checking), particularly at the ends of planks, should be expected with installations over radiant heat and does not constitute a product failure.
*Wood stability refers to predictable movement that can be expected in a given wood species after installation once in service. Note that even when using an ideal species for radiant applications actual wood performance can still vary due to the radiant system construction, it operation and installation techniques.
Technical and Installation
Answered on 6/27/2012 by cc-2