Solar Air Heater

  • How can solar energy be used to heat homes passively (without the use of solar cells or solar panels)?
  • What parts of the country or world might this be useful for?

Recommended Items:

  • Thermometer
  • Acrylic paint
  • Cardboard
  • Tape

Concepts used:

  • Air flow (convection), Color, Solar heating


The sun is a natural source of energy and a great source of heat. When sunlight is absorbed by an object the object will heat up. Different materials can get hot faster than other materials. For example leather seats in a car are hotter to the touch than fabric seats. Also, darkly colored objects absorb more light (reflect less light) than lightly colored objects, making dark objects hotter if they are left in the sun. It is also interesting to note that as air is heated it expands, thus causing it to rise. Conversely, cool air sinks. Because of this, it is possible to use this type of passive solar heating (heating just by using the sun’s energy without using solar cells or electricity) to actually heat a home.

In this experiment, take a sunny house window and cover it with cardboard (leaving an air gap between the cardboard and window). Paint the inside of the cardboard so that it absorbs as much heat as possible. Cut vents in the bottom and in the top of the cardboard. As the sun’s energy is absorbed by the painted cardboard, the trapped air between the window and the cardboard will heat. As it heats, the air will rise and escape through the vents cut into the top of the cardboard. This process will draw air from the room in through the bottom vents where that air will then be heated. Since the room air is cooler than the air heated between the window and the cardboard, this process will produce some warming in the room. In order to ascertain how much heating is possible and at what rate, multiple measurements should be made of the temperature of the air flowing in through the bottom vents and of the air flowing out through the top vents. Overall room temperatures can also be monitored to see how well the idea works.

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