Solar Air Heaters 101
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.