Build a Simple Solar Air Heater

This low-cost solar air heater plan lets you turn any south wall into a source of free heat.

| December 2006/January 2007

  • SolarHeater
    The author and the south face of his Montana home equipped with a simple solar air heater.
    Phot by Gary Reysa
  • SolarDiagram
    Side-view diagram of the solar air heater shows the air flow pattern.
    Len Churchill
  • solar air heater - Gary Reysa checking air flow
    The author, Gary Reysa, checks airflow.
    Joaon Reysa
  • solar air heater - diagram of collector face
    Front-view diagram of the solar air heater panel.
    Matthew T. Stallbaumer
  • solar air heater - materials for collector
    The solar collector is built from these simple materials.
    Gary Reysa
  • solar air heater - closeup of window
    This close-up through the polycarbonate shows the absorber screen, the foam sealer molding, screws with EPDM washers, battens and a bottom vent.
    Gary Reysa

  • SolarHeater
  • SolarDiagram
  • solar air heater - Gary Reysa checking air flow
  • solar air heater - diagram of collector face
  • solar air heater - materials for collector
  • solar air heater - closeup of window

After walking into my workshop one December morning and feeling a bone-chilling 10 degrees, I decided to install a heating system. Given the rising costs of propane and my family’s environmental concerns about using nonrenewable fossil fuels, a solar solution seemed fitting.

I’m a retired aircraft engineer, but you don’t need a similar background to tackle this project. In fact, a solar air heater built into new construction or added to an existing building can be an easy and inexpensive heating solution. Following the simple principles and plan outlined here, you can heat your workshop, barn or even your home with free heat from the sun. If it works here in Bozeman, Mont., it’s bound to work wherever you are.

I reviewed many solar collector concepts and decided to install a thermosiphon air collector on the south wall of the workshop. The elegant, simple thermosiphon design uses only the buoyancy of heated air to create circulation through the collector, eliminating the cost, maintenance and power consumption of fans, sensors and controllers commonly used in other collector designs. On a sunny day, in a cold climate like ours, this simple system can produce heat equivalent to burning about $2 worth of propane (equivalent to about $3 for natural gas).

To minimize costs, I integrated the collector with the structure and used readily available materials. It cost me about $350 and took only one trip to the hardware store. I built and installed it in about three working days. Follow the suggestions below, and you may be able to do it faster!!



How It Works

The thermosiphon collector consists of clear, corrugated polycarbonate panels fastened to 2-by-6-inch studs. The clear panels admit sunlight, and an absorber suspended inside the collector captures the sun’s heat energy. The air around the absorber warms, expands and rises, creating a convection current. Vents at the top and bottom of the collector allow air to circulate through it. Cool air enters the lower vents from the interior, is heated by the absorber, rises to the upper vents and returns to the interior. Air circulation continues as long as the sun shines on the collector.

At night, airflow reverses as air in the collector cools to outside temperatures. Simple flapper valves on the top vents stop this reverse circulation and keep the heat inside.

masonxhamilton
8/28/2018 9:38:30 AM

Don't over look the hot air that gathers in your attic. Most of our roofs are massive solar collectors. My insulation is on the ceilings, not against my roof. My attic is routinely about 20-40 F warmer than the house. I put a fan with an intake duct to the high point of the attic with a large dust and bug air filter on the intake. The system can be closed off from the house in the summer, but in the winter it blows warm air into the house until dark. I use a manual KISS on-off switch, but it could easily be thermostatically controlled to make sure the attic air was warm enough to be beneficial before turning the system on.


masonxhamilton
8/28/2018 9:38:05 AM

Don't over look the hot air that gathers in your attic. Most of our roofs are massive solar collectors. My insulation is on the ceilings, not against my roof. My attic is routinely about 20-40 F warmer than the house. I put a fan with an intake duct to the high point of the attic with a large dust and bug air filter on the intake. The system can be closed off from the house in the summer, but in the winter it blows warm air into the house until dark. I use a manual KISS on-off switch, but it could easily be thermostatically controlled to make sure the attic air was warm enough to be beneficial before turning the system on.


gordy
10/6/2017 11:49:17 AM

This story is from December 2006/January 2007. Gary has continued to work on solar heaters, visit his web site builditsolar.com for better heater designs. Or a sister site simplysolar.com . Thermosiphon collectors do work, BUT a lot of heat is lost through the glazing because of the high temperatures in the collector. To get the most BTU's from your collector you are better off putting fans on the unit and getting a large volume of cooler air (100f to 120f), than getting a small volume of hot air (180f and higher). The cooler you can keep the collector, the less heat escapes it to the outside. I use 2 computer fans (50 cent each at a flea market), powered by 2 - 7 watt solar panels, and controlled by a snap disk switch normally open (N.O.) close on rise at 85f (turns on) and opens on fall at 80f (turns off). The switch is in the collector at the top. Gordy







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