Buyer's Guide to Solar Heating

Image Gallery Solar hot-air collectors can warm your home’s interior - and blend seamlessly into its exterior. LEN CHURCHILL

Are you freezing in the winter to keep your fuel bill down? Or paying an arm and a leg to stay warm? Either way, it’s probably time to consider installing a solar hot-air system. There are several options, and these systems are a hot commodity right now — in recent months several suppliers have reported increased consumer interest.
Solar hot-air systems capture sunlight energy and use it to heat incoming air. Heated air is then transferred into your home, often with a small electric fan. The solar energy costs what it always has cost — nothing. Solar hot-air systems can help alleviate homeowners’ worries about rising fuel costs and provide years of inexpensive, maintenance-free comfort. They can heat homes, offices, workshops, garages and barns.

Solar Simplicity

All solar hot-air systems rely on hot-air panels or collectors. Collectors are typically mounted on south-facing walls, roofs or even on the ground, if it’s unshaded during the heating season.

Some commercial systems are simple thermosiphon collectors that rely entirely on convection to distribute hot air, but most use fans or blowers controlled by relatively simple electronics. A temperature sensor mounted inside the collector monitors internal temperature. When it reaches 110 degrees, it sends a signal to a thermostat mounted inside the home, which turns on the fan if room temperature is below the desired level. When the temperature inside the collector drops to 90 degrees, or the room reaches its setting, the thermostat turns the fan off.

Solar hot-air systems actively produce heat only in the daytime, but some of that heat is absorbed by the building’s thermal mass: drywall, tile, framing lumber, etc. At night, the heat stored in the thermal mass radiates into the rooms. The more thermal mass, the greater the nighttime benefit.

Hot Air vs. Hot Water

Solar hot-air systems are far simpler and easier to install than solar heating systems that circulate water as the heat-transfer medium. They’re also less expensive, and don’t use potentially troublesome chemicals or require complicated electronic controls. You can even build a solar hot-air system yourself (see “Build a Simple Solar Heater”).

Solar hot-air systems also produce heat earlier and later in the day than water-based systems. As a result, they may produce more usable energy over a heating season than water-based systems of the same size, according to the U.S. Department of Energy’s online publication, Consumer Guide to Energy Efficiency and Renewable Energy. Moreover, air systems do not freeze. Minor leaks in the collector or distribution ducts, which cause significant problems in water-based systems, also are less troublesome in hot-air systems. (Water-based heating systems do have one major advantage: They can store heat for use at night in water tanks inside the home.)