Since it's powered by the sun, and heats with hot air, the only mechanical or moving part is a simple fan that draws room temperature air into the heating panel through a series of heating channels, and then exhausts the heated air back into the room.

The basic solar window heater is 20" x 32" x 3.5" and framed in clear pine for painting or staining. Think of it as a box with an aluminum panel (collector) behind a sheet of air tight Plexiglas on the outside, and a sheet of thin wood on the inside to trap the collected heat.

Within the box are two baffles configured to look like a maze. This allows for a continuous stream of air to be heated as it is drawn through the box by the fan.

The aluminum collector panel is finished in flat black to maximize heat absorption from the sun. On a day with full sun, the panel will reach temperatures of 140 - 170 degrees.

A newer version of the solar window heater replaces the aluminum panel with high quality copper, also finished in flat black.

Located inside the panel is a thermostat switch. When the temperature of the heated air reaches 120 degrees, the switch automatically turns on the fan. When the air temperature cools to 90 degrees or less, the fan shuts itself off.

The small, efficient fan will move 102 cubic feet of air per minute or about 6,000 cubic feet per hour. The cost of electricity to operate the fan is around $3.00 per year.

The basic model sells for around $150.00. The newer, copper lined solar window heater sells for an additional $10.

The electrical components are available separately for $42.95. They include the fan, thermostat, junction control box and transformer. If you're handy, you could probably build your own solar window heater for around $80.