For hardwood floors laid over a subfloor with a radiant heating system, do not raise or lower the temperature by more than 5°F per day and never exceed a surface temperature of 80°F to 85°F.
While floor-heating temperatures do not harm the wood, it does affect its moisture content and variances in moisture content will cause the floor to move in numerous ways. Moisture content is a key factor to successful floor performance and adding heat to the floor makes attention to moisture even more critical.
As the temperature goes up, the moisture content generally goes down. Heating the wood too much will cause it to shrink and gaps will occur between the boards. Once the temperature is lowered, the moisture returns and the gaps close up. Low, even temperature distribution is the key. Uneven heating of the floor can cause cupping.
In most climates, winter air is dryer than summer air. This can cause seasonal gapping between boards and willoccur regardless of whether or not there is a floor heating system installed. If an indoor humidity control is not present,occupants should expect some degree of seasonal gappingon any wood floor with or without radiant heating.
Temperature and humidity levels must be kept uniform, the ideal levels are 60°F to 85°F and 35% to 55% relative humidity.