MOTHER's Solar Air Heater

Because an earlier version of this solar air heater included an expensive, hard-to-obtain material, MOTHER EARTH NEWS' crack research team has come up with this alternative version.

| November/December 1978

solar air heater - diagram

Diagram shows air flow patterns generated as sunlight falls on the solar air heater.


The article "DIY Solar Heating with the Heat Grabber" featured a very interesting little solar air heater. The unit could be built in less than two hours for just $2.56 a square foot ($32.18 total). It fit right into any south-facing window that could be opened. And all by itself, it could heat a reasonably well-insulated room almost anywhere on the continent on almost any sunny but otherwise frigid day.

And it still can (which is why so many hundreds of people here in the U.S. and in Canada have constructed and are using our device).

The only real trouble with that original heat grabber, in fact, is the Celotex Thermax TF-610 that MOTHER EARTH NEWS' researchers specified as the major material for its construction. Dang it! The highly insulative and easy-to-work construction board simply isn't available in many parts of the country. And when it is available, we've had reports that various suppliers aren't above charging double for what little TF-610 there is to go around.

So here's our solar air heater all over again, only this time we're mostly fabricating the unit out of wood. The bad news is that it'll take you about six hours to construct this version. The good news is that [1] it'll cost you only $2.50 per square foot tops—and far less than that if you can scrounge up your lumber—to build this one; [2] this is a more rugged unit; [3] you should have no trouble finding everything you need for this version, and [4] we've added some refinements and improvements that if anything make this second heat grabber even more efficient than the first.

Before you start putting your own Btu-catcher together, though, remember this important fact: For maximum effectiveness, you should "custom design" your solar air heater to rest in a window at an angle up from the horizon equal to your latitude plus 10°.

This adds up to 45° for MOTHER EARTH NEWS' North Carolina offices (which are situated 35° north of the equator). And that's what we get when we cut both sets of boards on the sides of the unit (where the "collector" portion of the air heater meets the furnace's "window box") off at an angle of 67.5°.

catia hirsch
1/6/2013 3:52:58 AM

All my windows slide. No window sills. How can I mount it sideways?

11/30/2010 3:48:50 PM

All my windows slide. No window sills. How can I mount it sideways?

11/30/2010 3:46:10 PM

All my windows slide. No window sills. Can I mount it sideways?

11/14/2010 2:34:20 PM

I have one small problem with constructing this in the south window; I do not have one. Has anyone an idea on how to build around the corner to my window?

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