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Simple Solar

A chilly room in my house faces south, but has only one small window for the sun to shine in. Is there an inexpensive solar heater I can put in the window for more free heat?—Sam W.

Whole-house solar heating is not always economically feasible, but making a small one yourself for just one room almost always pays back its cost very quickly. Building one will be a good family project to get your children interested in conservation.

Solar energy can also cool your house during the summer by creating a natural breeze through temperature differences. Also, cutting peak electricity demand during hot summer afternoons is good for you and your electric co-op.

I built a small solar window heater in my home, and it produces warm air at about 120 degrees on a sunny day. During the summer, it functions as a nonelectric exhaust fan to create a breeze through my home.

I spent about $100, but mine is fancy, with aluminum trim on all the edges and a double-pane top of clear acrylic plastic. You should be able to build one for about $50 or less if you have some scrap plywood and wall studs and an old storm door or window.

A solar window heater is basically an insulated flat box with a clear top and a divider panel inside to create two shallow chambers, one above the other. The divider panel is shorter than the box so the chambers are connected at the outdoor end. One end of the box is mounted in your window opening and sealed with weatherstripping against the sash and the window frame. The other end slopes downward outdoors with a clear top facing the sun’s rays.

The inside of the box is painted a flat black to act as a solar collector, heating the top chamber where the air expands and becomes less dense. This less-dense heated air flows up the sloped solar heater and into the room, creating a draft that draws air from the room into the bottom chamber.

It helps to insulate the top chamber from the lower one to increase the temperature difference. It is critical to insulate the outside walls of the box so the room air flowing down the lower chamber does not lose heat to the cold outdoor air.

The proper angle to slope the heater depends upon your climate. The farther north, the steeper it should be, because the winter sun is lower in the sky. Try different angles to see which warms your chilly room the most. A steeper slope may provide more airflow, but the output air may not be as hot.

Since I live in Cincinnati, which gets below zero some days, I built a clear top with two layers. I drilled several tiny weep holes in the lower edge to allow condensation to escape. I also screwed L-shaped aluminum angle stock (from any hardware store) on the divider collector panel in the warm chamber. The angle pieces increase heat transfer and also create air turbulence. Aluminum is an excellent heat conductor, so the air swirling around the pieces increases the heat flow.

For free cooling ventilation, install a hinged door in the top of the heater immediately outside the window. During the summer, block the top chamber warm-air opening from the heater to your room and open the outdoor hinged door. On a sunny day, the solar-heated air will exhaust out the hinged door and draw air from inside your room for a natural breeze indoors.

Write for Utility Bills Update 442, a list of solar window heaters Include $3.00, a business-size SASE, and Update number. Mail requests and questions to James Dulley, Kentucky Living, 6906 Royalgreen Drive, Cincinnati, OH 45244. Go to to instantly download.

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