Dear Umbra,
We’re trying to build a really small house and be really economical as we do it. Radiant floor heating sounds practical for the first floor, although it’s expensive. What do you think about radiant floor heating, pluses, minuses, efficiency?
Radiantly yours,
Kerry
Florence, Mass.
Dearest Kerry,
Thank you for helping me to write about radiant floor heat basics by sending in your question as requested. How I have coveted a nice radiant floor.
And these little piggies were all warm and toasty.
Photo: iStockphoto
Radiant heat, also known as infrared radiation, heats your floor (and thus you) directly, instead of blowing air around. This is usually achieved through tubing laid below the floor. A classic installation would be a new floor, with insulation laid down, then hydronic tubing arrayed atop the insulation, and concrete poured over to form the body of the floor. Sometimes tiles are a final touch. A boiler or solar-heating system attached to the tubes circulates warm water through them, which warms the floor, which warms you as you happily scoot about in your bare feet. Electric radiant tubing exists but is less common. The tubes can also be installed under a wooden subfloor, between the joists, if you have access there. “Wet” installation in concrete is said to be the most efficient use of the technology, however.
Radiant floor heat has a number of comfort advantages over other common systems. You feel warmer with the thermostat at the same temperature, you get to walk around barefoot in the winter, there’s no forced air recirculating so there tends to be less dust, it’s silent, and there are no heat registers or radiators on the walls blocking your ideal furniture arrangement. It’s lovely, really. Great for someone who likes to lie about on the floor — and of course all the advertisements depict dogs and crawling babies partying down.
These systems have some energy-efficiency advantages, as well. They’re usually more efficient than forced air, partially because hot air is lost through forced-air ducts before it reaches its target, and are more efficient than baseboard heat. Also apparently radiant floors allow less infiltration by cold air from the outside, known as a “stack effect” — I don’t fully understand this, to be honest, but from what I can tell, hot air normally creates a pressure differential as it rises and exits the house, and cold air in turn enters the house. This happens less with radiant heat because there’s no phase where the house air gets hotter than the thermostat temperature. There also are claims that persons keep their thermostats set lower with radiant floors because they feel warmer at lower temperatures, but this is largely unproven.
Which leads us to the juicy article from Building Green that makes a persuasive argument that radiant floor heat is not necessarily the best choice for new green construction.
Remember, we’ve discovered over the years that the important first steps in green home design, including and especially remodeling, are to button down the house. Insulating, reducing leaks, reglazing or replacing windows, all come before the sexy radiant heating system. After the house shell has been made more energy efficient, then we can gauge the correct size of our heating and cooling systems. This juicy Building Green article makes the case that in well-built homes, radiant heat is not worth the costs, because the heating load of the home will be quite low. The article is quite thorough with its evaluation, so give it a read as you consult with your local expert. Apparently radiant systems can be very expensive, in the realm of $10,000. All else being equal, that right there is the main downside.
Still, they are dang cozy.
Dreamily,
Umbra
