Radiant floor heating

With spring just around the corner, it feels like the wrong season to think about heating systems. But now's the time to consider how space heating options mesh with building or renovation plans for the upcoming construction season. One of the most comfortable, efficient and pleasant ways to heat your home is with a series of liquid-filled heating pipes built into your floor. This is called a radiant floor heating system and the technology has been around for almost 20 years.

Here's How It Works

The floor-mounted pipes that form one part of the system can be encased in the concrete that forms a slab-on-grade floor, or fastened to the underside of a conventional wood subfloor, using metal brackets. The pipes are connected to a boiler that heats water or antifreeze. The warmed liquid is then pumped to every corner of the floor where it gives up heat to the surroundings. Systems differ, of course, but the piping of a radiant system can be installed by any handy homeowner with simple tools. Leading manufacturers include: Ipex (866-473-9462; www.ipexinc.com), Radiantec (their free installation manual is worth the long distance call to Vermont - 802-626-5564; www.radiantec.com), and Thermo Floor (800-356-7887).

Heat Source Options

Pipes in your floor are only part of the deal, of course. The actual heat must be generated by a boiler of some sort, then piped into your under-floor network. The boiler can be an existing unit you're already using (perhaps with conventional radiators), a new boiler, or even a domestic hot water heater. This last option is especially attractive because it can also supply your household hot water needs. Although this sounds good on the surface, don't get your hopes up too high. There are limits to how much space heating you can expect from a water heater. A typical 40 gallon electric model, for instance, generates only 3500 watts of heat -- that's a little more than what you'll get from two portable, plug-in heaters. And don't forget you'll need to siphon off some heat for your hot water needs too. A gas water heater packs a much greater energy wallop than an electric one, but it's capacity is still low compared with typical boilers. If you have a small, well-insulated home, it can probably be heated with a large, gas-fired hot water heater. A general rule of thumb is that you'll need a heat source capable of generating 30-35 btu/hr (British thermal units per hour) of heat per square foot of floor area to keep a normally-insulated home warm down to 40 degrees below zero. At this rate, a 40 gallon gas-fired water heater will heat a 1200 sq. ft home on the coldest days. Another plus is the fact that the best, modern gas-fired boilers and water heaters don't need chimneys. They can vent through a wall with ordinary ABS drain pipe.

What About Leaks?

According to the manufacturers I've contacted, the best polyethylene piping used for radiant heating systems has a life expectancy of 100 years. Time will tell, of course, but even half that lifespan would be fine for most of us. Pipe problems can arise sooner, however, if physical damage occurs by nails, saws, drills or other implements of the renovator's trade. Broken pipes are a possibility, but they can always be fixed; sometimes easily, sometimes not. If your pipes are installed under a wood floor and remain accessible from below, then it's a simple matter to splice in a repair coupling at the break. Repairs to pipes encased in a slab-on-grade concrete floor require you to chisel into the concrete, complete the reconstructive surgery, then patch the entry point with new concrete.