Buildings

Radiant Floor Heating

Q: My wife and I are planning a new house, and we've decided we want radiant floor heat, since it's the most efficient. We have our own well, and it seems to me that if we have water circulating through the floor it could also be used in the summer to cool the house, but I've never heard of anyone doing that. Will it work? If not, what's the best way to cool the house?

A: First of all, I'm not sure that radiant floors are the "most efficient" type of heating. I've been in a number of homes with radiant floors, I've talked with dozens of people who have them, and I am convinced of one thing: they are extremely comfortable in the winter. Most people, in fact, who have lived with radiant heat in any of its forms-hot water radiators or baseboard units, radiant wall or ceiling panels, passive solar, and even radiant wood stoves-tend to get a far away, contented look when talking about the comfort of their homes in winter.

In theory, since a warm floor heats up your feet, you will be comfortably warm at lower air temperatures, so the heating system will, in fact, provide comfort using less fuel than a conventional system. In addition, warm surfaces-walls, windows, ceilings, or floors — tend to "suck" less heat from your body and will provide comfort, even if the air in the room is cooler.

That theory makes sense to me, but I haven't seen any research showing that homes with radiant floors actually use less energy, and if they do, how much? If, for instance, you spend much of your time with your feet propped up in the Lazy Boy, I'm not sure the warm floor will have a big impact on your bill.

In financial terms, part of the problem is the one you've identified. Is there a way to heat with radiant floors and not have to spend the money for a forced air cooling system on top of it? The idea of circulating cool water through the floor seems to come up a lot, particularly from folks who have their own wells and figure they can circulate 55 o water through the slab to pull heat out of the house.

We know what happens to a cool ice tea glass when set out into a hot, humid room. Water condenses out of the air onto the glass. Similarly, if your strategy were successful, your floor would be cool enough to make moisture in the air condense, turning your entire house into a gigantic Slip 'n' Slide.

An air conditioner blows hot, humid air over a cold coil, the water condenses on the coil, drains into a pan, and then into the drain or the yard. Turning your entire floor into a huge condensate pan might be fun for the kids, but not so cool for the rest of us.

There are other strategies that can work. First, build your house tight and make sure you get a really good insulation job, not the typical low-bid job. Install a mechanical ventilation system for fresh air and moisture control. Use as many of the traditional methods of keeping heat out of the house as you can: minimize west- and east-facing windows, use wide overhangs, preserve or plant shade trees, or shade the house with porches, particularly on the west and east sides. High ceilings and paddle fans can both reduce the need for cooling.

Once you've reduced the cooling load, you can air condition the house in several ways that don't involve duct systems. High-efficiency window air conditioners mounted through the wall can be effective, very low-cost to install, and reasonably energy-efficient. The biggest problems are proper placement and noise. Similarly, through-the wall units, like those commonly found in motels, can be used to cool the space at relatively low up-front cost, but also tend to be noisy enough to annoy some people.

A newer type of air conditioner, called the "mini-split" system has some very attractive features for your situation. It uses an outdoor unit very similar to a conventional air conditioning system, but instead of a big air handler and duct system, panels are mounted inside various rooms. The panels, which look like window-type A/C units from the front, are only several inches thick, and they can be mounted anywhere, including on interior walls.

These systems are not cheap, but could be less expensive than installing a whole duct system in the house. The ones I've heard are much quieter than window or through-the-wall units, and the flexibility of being able to install them on interior or exterior walls is a big plus. Some of them have sophisticated electronic controls with a remote, so the family males will love it. So don't make them slide across a wet floor.