Question: Radiant floors are touted as saving energy, although they’re fairly expensive. A 2002 BuildingGreen.com article, Radiant-Floor Heating: When It Does-and Doesn’t-Make Sense, suggests that radiant floors aren’t necessarily a good option in passive solar or superinsulated homes. Is that still accurate today or have there been recent developments we should know about? – Cynthia Free, Portland, Oregon
Answer: Radiant-floor heating is a great heat-distribution option … for lousy houses. In new construction, I argue that it makes a lot more sense to take the $10,000 or more you would spend on a radiant floor slab and put it into the house envelope (R-40 walls, R-60 roof, R-20 foundation, triple-glazed, double-low-e windows, etc.). Get the heating load so small that just a small woodstove or electric mini-split heat pump would provide all the heat that’s needed; in a compact house you won’t even need distributed central heat. It’s not only a matter of economics, but in a superinsulated house, a radiant slab isn’t a good thermodynamic fit, because to avoid overheating the space the slab temperature has to be kept so low (just a degree or two above the air temperature) that it won’t even be warm to the touch.