VIDEO- A Home Built thermo-siphon solar air heater in Bozeman, Montana


With this short video program General contractor Peter Brown describes an innovative owner built residential solar air heater on a garage in Bozeman, Montana. This solar air heater takes advantage of this garage’s very large south facing wall. The simple passive thermo-siphon design uses only the buoyancy of heated air to create circulation through the collector.



How it’s built

This collector is a series of 4’ wide 2-by-6 frames attached to the side of the building. A series of vents are cut thru the wall into the building at both the top and bottom of each frame. Within each 2×6 frame a strip of common black aluminum window screen material is suspended. This black vinyl screen acts as an absorber to capture the heat energy from the sun. Clear corrugated polycarbonate panels cover the frame and screen to provide an airtight exterior seal over the solar air heater.

How it works

Sun light passes thru the clear panels, and is absorbed by the aluminum screen. The air around the screen warms, expands, and rises, creating convection current. The vents that pass through the wall at the top and bottom of the solar air heater to allow air from within the building to circulate through it. Cool air enters the lower vents, is heated by the absorber while it rises to the upper vents where it returns to the interior of the building, as much as 80 degrees warmer. Air circulation continues as long as the sun shines on the collector, and the sun does all the work – there are no moving parts to wear out. Simple back-flaps automatically prevent reverse airflow at night or on cloudy days. During summer, the higher angle of the sun means no unwanted heat is created.  During winter in our sunny climate these heaters work exceptionally well and are augmented by reflection of sunlight off the snowy ground in front of the collector.

Readily available components

The homeowner was able to build this heating system using common materials that are readily available in local hardware stores. He was able to build and install it in about three working days.

Energy savings

With the aid of data-logging equipment the homeowner monitors the energy produced by the solar air heater and concludes that it produces about $350-400 worth of heat per winter! With this simple technology you can heat arenas, barns, workshops, garages, commercial and industrial spaces or even your home with free heat from the sun


  1. I am considering adding this system to the south-facing wall of my attached two-car garage. I live in WI. I am curious as to your thoughts about possibly filling the stud cavities behind the collector with concrete instead of insulation. I would remove the siding and use black sheathing behind the collector. I figure this would help maintain the temp longer into the evening. I don’t know if this would be better than adding double glazed panels in a cavity or two or not.

  2. Nice job with the video Gary. This system is ideal for your situation. The sun’s reflection off the snow really works. simple plastic flaps to prevent heat loss… very nice.

  3. I have a south facing porch on a second floor with a ~30″ x 20′ high railing that I want to install a passive solar panel upon. I issues I see are that since the panel will be exposed to ambient temperature on both front and back I will need to insulate the 5 non front sides to hold heat. I could easily use 2′ closed cell foam at a minimum and uses insulated heat ducting to bring the heated air to the house. I suspect a problem with using convection so a thermostatically controlled fan may be necessary to push(pull?) air through the heater. Do you see any flaws in this plan of have suggestions to increase efficiency? Located near Hibbing MN. Very cold temps very high electricity costs (co-op rip off $45/mo. before turning on a single light)

  4. Jim McDonald

    Considering building some of these to heat my 40 x 40 shop. Thinking of using cement board (the kind used as underlayment for tile floors) painted black as a heat sink. Would add a bit more to the weight of the collector, but suppose that could still be feasible.

  5. Gerry

    Hey Mike I applaud your efforts to install one of these. I’m doing research myself on solar heaters for a cabin in northern Minnesota. in my research I’ve come across a few YouTube videos in which people have mounted a solar panel outside their garage / shed which powers a small fan to provide more flow. if you are any sort of computer programmer, there are also programmable devices that you can install which will read from a thermometer inside the solar heater and once the temperature reaches a certain threshold the device will trigger the fan to turn on. thus not having to worry about backflow at night or running when its cold. unfortunately now that I say this I can’t locate the YouTube video which pointed out that design but I’m sure it’s easily found in many YouTube videos. good luck and let us know how it turns out.

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