Solar Heater Can Go in Window
QUESTION: We have a room with a south-facing window. How can I make a small, inexpensive solar heater that mounts in the window? I don’t want it to show from indoors and I would like to remove it in the summer.
ANSWER: There are several basic designs of small do-it-yourself solar heaters that you should be able to make over a weekend for less than $50 in materials. One can produce enough free solar heated air (at about 100 degrees) to keep a room comfortably warm on a sunny day.
The simplest type of solar heater mounts in your window and angles downward outdoors. The window closes down against the shallow (less than one-foot high) air inlet and outlet. It is barely noticeable from indoors.
If you air condition your home in the summer, you can easily remove the solar heater and just close the window as always. If you rely on natural ventilation, you can add a summer vent door in the outdoor portion of the heater. By opening this vent, the solar heater becomes a free exhaust fan by naturally drawing hot air out of your home.
Most do-it-yourself solar heater designs use a shallow plywood box with a clear top. An old storm door or window works well for the top. Mount the box in the bottom of your window and angle it downward outdoors.
The box is split inside by a collector divider panel (painted black) that creates two shallow chambers, one over the other. The divider panel is shorter than the box leaving a gap at the bottom that connects the chambers.
The sun shines through the glass on to the black divider panel and heats the air above the panel in the upper chamber. This hot air naturally rises upward (since the box is angled upward to the window) and flows out into your room. Cool room air is then drawn into the lower chamber.
You can increase the overall efficiency of the solar heater by insulating the sides and bottom of the box. This reduces the heat loss from the room air entering the heater and from the solar heated air as it flows back into your room. Since the solar heater does not get extremely hot, you can easily attach rigid foam insulation to the sides and bottom.
There are several designs you can use for the divider panel. A plywood sheet with insulation attached to the bottom is effective. You can also lay fiberglass insulation over the panel and paint the vapor barrier black.
Another design uses a corrugated aluminum collector sheet directly under the clear cover. The air is circulated beneath it in insulated chambers. This reduces heat loss back outdoors through the clear top.
You can write to me at the address below for Utility Bills Update No. 403 showing simple do-it- yourself instructions and diagrams for making several designs of solar room heaters. Please include $1.50 and a self-addressed business-size envelope.
Letters and questions to Dulley, a Cincinnati-based engineering consultant, may be sent to James Dulley, Los Angeles Times, 6906 Royalgreen Drive, Cincinnati, Ohio 45244.
