“In-floor radiant heating systems save energy.”
Proponents of in-floor radiant heating systems often claim that such systems save energy compared with conventional heating systems. The idea is that people living in homes with warm floors are so comfortable they voluntarily lower their thermostats, thereby saving energy.
The only problem with the theory is that no reputable study has ever shown it to be true, while at least one study has disproved it. Canadian researchers visited 75 homes during the winter to note where the homeowners set their thermostats. The 50 houses with in-floor radiant heating systems had thermostats set at an average of 68.7°. This was actually a little bit higher than the thermostats at the 25 homes with other types of heat delivery (either forced air or hydronic baseboard), which averaged 67.6°F (see Notebook, 12/01). The researchers concluded, “There will generally be no energy savings due to lower thermostat settings with in-floor heating systems.”
Other radiant-floor proponents have suggested that homes with radiant floors have lower boiler temperatures compared with homes with baseboard units. This factor, however, would be responsible for only very minor energy savings, if any. It has also been suggested that homes with radiant floors might have reduced infiltration compared with homes with forced-air heat. While this is certainly possible, high infiltration rates are best solved by addressing air-barrier problems at the time of construction.
Radiant floors, like baseboard radiators, are heat-distribution systems. When it comes to heat distribution, a Btu is a Btu. The overall efficiency of a hydronic heating system is basically governed by the boiler; the distribution equipment plays only a minor role in system efficiency.
Finally, it should be noted that a home with a slab-on-grade radiant floor heating system may lose more heat to the ground than a home with a forced-air heating system would — a factor that might lower the radiant heating system’s overall efficiency. The best way to counteract this problem would be to increase the thickness of insulation under the slab.