How to Build Homemade Passive Solar Air Heaters

Written by ruth de jauregui Google
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How to Build Homemade Passive Solar Air Heaters
The sun is a valuable energy resource. (Sun image by KPICKS from

Passive solar air heater exchangers are simple devices that take advantage of the fact that hot air rises. A solar air heater can easily be built at home in a south-facing window, using foam core board, black paint, duct tape and a thermometer with a sensor. This project can be done by a parent and child in an afternoon.

Skill level:

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Things you need

  • 2 sheets foam core board
  • Flat black paint
  • Exacto knife
  • Metal ruler
  • Duct tape
  • Thermometer with a wire sensor

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  1. 1

    Choose a south-facing window and remove everything on the windowsill. Clean the window thoroughly.

  2. 2

    Cut the first piece of foam core board a little smaller than the window. On the bottom edge, using the exacto knife and metal ruler, cut out several 1-inch-high by 6-inch-wide strips, so it has "feet." Paint the board flat black on both sides.

  3. 3

    Cut the second piece of foam core board to exactly fit into the window. Do not paint it, leave it white. Cut a similar set of feet on the bottom edge. On the top edge of the board, mark several 1- by 2-inch notches. Cut down one inch, but only score the bottom edge. Carefully fold the strip inward, so it makes a flap. Cut three or four of these flaps, spaced equally across the top of the board.

  4. 4

    Using duct tape, carefully tape the top edges of the flaps on the white board to the top edge of the black board. The bottoms of the two boards will not be even. Place the assembled air heater in the window.The bottom edge of the black board is on the inside, angled toward the window glass, and the white board just fits into the inner edge of the window. The flaps should hold the two boards apart so air flows between them. Duct tape the sides of the white board to the wall so it holds the entire unit in the window. Do not tape the top and bottom.

  5. 5

    Mount the thermometer on the wall and insert the sensor inside the unit, on the top. The cooler air of the room will flow in on the bottom of the unit, past the feet. As the sun shines in the window, the air warms and rises, flowing out of the top of the air heater. Depending on the season and time of day, a solar air heater can provide a significant change of temperature.

Tips and warnings

  • If you have several south-facing windows of the same size, this would make an interesting science fair project. Vary the colours of the angled board as the variable in the project, documenting the temperature variations between, for example, a white, a red, a green and a black board.
  • You can purchase black foam core board at art supply stores.
  • Make sure the solar air heater is easily removable from the window in case of emergency.
  • Use caution with the exacto knife; it is very sharp.

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