Simple Solar Unit Can Heat Room
QUESTION: I want to build an inexpensive (less than $100) solar heater myself to cut my high heating bills. I want it to be able to heat one large room and a small one. What simple do-it-yourself design do you suggest?
ANSWER: There is a simple design of solar heater that you should easily be able to build yourself for less than $100 in materials. On a sunny winter day, in a mild climate, it should easily produce enough hot air to keep your rooms comfortably warm.
This is a very simple air-type solar collector. Room air is heated as it circulates through the solar collector. You can mount the collector flat against your pitched roof, tilted up for greater efficiency, or against a south-facing wall.
The simplest design relies on “thermosiphoning.” This means that the less-dense warm air naturally flows up and out the top outlet. This draws cool room air in the bottom inlet to be heated, developing a continuous flow.
This design concept uses a slanted perforated metal collector sheet (painted black) inside a shallow insulated box. The sun shines on the collector plate and heats it. With it slanted inside the box, the room air is forced to pass through the openings in the hot metal sheet as it circulates from the inlet to outlet opening through the solar heater.
For even greater heat output, you can install an inexpensive electric blower. For a 4- by 8-foot collector, a small 100-cubic feet per minute (cfm) blower should be adequate. This also allows you to tilt it properly toward the sun for the greatest efficiency.
For the most inexpensive design, build a shallow box with 1/2-inch plywood. Make it 4 feet by 8 feet so that you can use standard size lumber. Leave the top of the box open. You will later cover the top with a glass or clear acrylic plastic sheet. Acrylic is inexpensive and easy to work with.
Using expanded metal lath is the easiest way to make the metal collector sheet. Wire three or four layers of it together, staggering each one a little to offset the openings.
In this way, the sun shines on most of the metal of each layer, yet the room air can easily flow through. Punching or drilling holes in aluminum sheets and spacing them slightly apart is also effective. Saw an inlet and an outlet opening in the ends of the box nearer to the open side.
Lay standard foil-backed fiberglass wall insulation in the bottom of the box. Mount the metal absorber plate slanted above the insulation. Attach the clear cover on the top and seal it.
During mild summer weather when you are not air-conditioning, use your solar heater as a natural whole-house ventilator. Disconnect the hot air outlet from your house and it will draw cool outdoor air in your windows.
You can write to me at the address below for Utility Bills Update No. 349 showing do-it-yourself instructions, diagrams, and materials list for making the above simple solar heater. Please include $1.50 and a self-addressed business-size envelope.
Aluminum Siding Gap Allows for Expansion
Q: I have aluminum siding on my house. There is a gap between the flashing around the window and the siding. Shouldn’t this gap be caulked to stop air leakage and rain?
A: The gap should not be caulked if the siding was installed properly. Metal siding, especially aluminum, expands as the temperature changes. The gap is necessary to accommodate this expansion without buckling.
The flashing around the window frame probably was caulked and nailed in place before the siding was installed. This provides the seal. Caulk the other openings without flashings, such as electrical outlets and faucets.
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.
