What are solar air heaters?

Is a solar air heater a good solution for your home? Let's talk first about what it is and what it isn't. A solar air heater is an active system as opposed to a passive system. Passive solar systems rely on heat absorbing structural materials and building orientation that takes advantage of southern exposure. Active solar systems use solar panels to collect solar energy and fans to move the energy to a different place.

A solar air heater is intended to supplement your existing heating system, not replace it. The most efficient way to utilize a solar air heater is to install it where it can blow or diffuse warm air directly into a room that sees a lot of daytime use. Drawing on the principle that warm air rises and cool air sinks, the solar air heater pulls cooled air from the bottom of a room, circulates it through the solar collector where it picks up heat, then blows the warmed air back into the room.

Solar air heaters use roof, wall or window mounted solar collectors to heat the air that passes through them. The solar collector must be mounted on a south-facing roof or wall where it gets full sun exposure that isn't obstructed by trees, tall buildings or other shade producers. Smaller window units can be mounted under a sunny south-facing window. This type of solar air heater extends through the window, so you won't need to install any ducts or vents to enable air flow. These simple, direct-transfer systems don't store heat, so they won't work at night or on cloudy days.

Some larger systems use heat sinks, which consist of materials that can absorb and hold heat for a short time. During the day, excess heat is transferred to the heat sink for storage; when the sun goes down, heated air is transferred from storage to your house. Although a heat sink might extend your use of solar thermal energy into the night, incorporating one into a retrofit heating system is expensive. It can also be hazardous to your health. Moisture that collects in a heat sink fosters mold and bacterial growth on the rocks. When the blower pulls warm air from the heat sink, it also gathers up these contaminants and blows them into your home.

On the next page, we'll talk about costs, installation and maintenance for a solar air heater. Keep reading to see if it's a viable solution for your home.

Depending on the complexity of the system, commercial solar air heaters range from under $1,000 for single room heating to $6,000 for large-space or multi-room applications [source: Darling, altE]. But keep in mind that these are supplemental heat sources; you'll still need your conventional heating system. Solar systems designed to provide central heating aim to replace 40 to 80 percent of conventional heating. They're most cost effective when providing 50 percent of the home's heat [source: NC Solar Center, U.S. Department of Energy]. A simple room heating unit, of course, won't cut your heating costs by that percentage. It will, however, reduce the amount of conventional heat you need to keep your home comfortable.

Installation is an extra expense. Simple unit installation is within the capacity of an experienced DIY-er, but solar air collectors measure around 4 feet (1.2 meters) wide by 7 feet (2.1 meters) high. And they're heavy, so you'll need a helper or two to mount one on a roof. You may need a building permit, and you'll definitely need to make sure that adding the collector to the roof won't exceed its load limit. Larger or more complex systems require ductwork and electrical wiring, but commercial manufacturers are making strides to simplify installations with integrated fans and thermostats that you can plug into existing outlets in your home. If you choose to hire a contractor, look for one with experience in solar installation technology.

Each home is different and climate conditions range widely from place to place, so how much money a solar air heater shaves off your heating bill depends on the condition of your house and where you live. If your house is poorly sealed and insulated, installing a solar heat unit won't save very much energy; solar heated air leaks out just as quickly as conventionally heated air does. Solar air heaters do their best work in areas with long, cold, sunny winters. In warmer regions with short winters, designing the system to do double-duty for household water heating during the summer increases cost effectiveness and accelerates ROI. This is more complicated than adding solar room heating. It requires the addition of an air-to-water heat exchanger to the system. Some designs also require plumbing. Like the solar air heater, this is supplemental energy. It won't replace electricity or natural gas for water heating in most climates, but you can make it work to reduce the cost of this function.

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