Make a Simple Solar Air Heater

Heat a room or outhouse with a solar heater made from recycled aluminium cans

Using the sun to heat water (1) is a very cost effective way to save energy. Typically payback on even the most expensive systems is under ten years, with DIY Solar Water Heaters (2) paying for themselves in just a few months. Similar techniques can be used to make a Solar Space Heater - a device which warms the air inside a room or building.

Solar Garage Heater

Pictured above is a simple small passive solar heater made from recycled aluminium drinks cans and used to heat a garage. If the building to be heated is well insultated, a solar heater such as this can lift the temperature by a significant number of degrees. A larger heater or a number of similar heaters can be used to heat larger spaces, or to heat smaller spaces to a higher temperature.

Offcuts of 2 x 4 and a sheet of plywood were used to build a box to tightly hold 5 rows of 10 black-painted aluminium drinks cans. The inside of the box was then sealed using caulk to prevent hot air from escaping. Cold air is drawn in from a hole at the bottom of the box, and the heated air emerges from the top passing through a pipe into the garage to be heated. A plexi-glass sheet was glued to the box to let sunlight in but not let the hot air escape.

Click here to find out more about this basic almost free garage heat (3) project. Read on to find out how to make your own solar heater.

Building a Solar Space Heater

This type of solar space heater works by drawing the air to be heated into the bottom can of a column of cans. The air is then heated inside the cans by the sun's energy and the hot air within them rises upwards (thanks to convection) to be fed into a pipe which re-enters the building to be heated.

Building the Box

First of all make a box out of whatever scrap materials you have to hand. Set the dimensions to that the width of the interior of the box is exactly the same as the width of however many columns of cans you would like to use in your heater.
The height of the box should be the same as however many cans you would like to have in each column plus a few centimeters.

For increased efficiency, you may choose to insulate the box to prevent heat escaping (by conduction) through the plywood. If so, size your box so that the cans and insulation will fit snuggly.

Drilling the Cans

For the air to pass through a column of cans, holes must be drilled into them. Remember that there is already a hole at the top of each can out of which the drink is poured. That just leaves holes at the bottom of each can to be drilled.

In the bottom can of each column a 1/2 to 1 inch hole is drilled in the side. (see image below)

Drill a hole in the side of the bottom can of each column

The rest of the cans in the column have a similiarly sized hole drilled into the bottom. See image below)

Drill holes in the bottom of all of the other cans

Building the Can Columns and Painting

Then the cans of each column are glued together using caulk or silicon adhesive and painted using black paint to help them absorb the sun's energy. Barbecue or fireplace/stove paint is excellent for this as it will not flake off, but any marine grade paint will do a similar job - just make sure it has a totally matt finish.

Cans painted black inside the solar heating box

The inside of the box must also be painted with the same paint before the columns of cans are glued into position using caulk or silicon adhesive. The outside of the box should be treated with preservative, varnish, or paint to help it survive the elements for many years.

Sealing the Solar Heating Box

Ideally the whole unit will be sealed with a sheet of tempered glass - of the type used in car windscreens. This glass is very strong and resilient to heat. However, tempered glass (unless you can find and recycle a sheet) is also very expensive. Therefore plexi-glass (plastic) can be used, but it will degrade far more quickly and become opaque blocking out the sunlight.

A hole at the top of the box acts as the hot air outlet and can be connected to the building/room to be heated using an insulated pipe.

Possible Improvements to the Design

Pictured above is an alternative design in which the cans are all joined together in a snake. The illustrations shows an array of just 3 x 3 cans for simplicity however hundreds of cans could be joined in this way to make a larger heater.

Air inside this snake would rise much more slowly through the heater (than was the case in the previous design) since it has a much longer path to travel, and it is obstructed from rising straight upwards. Therefore the air can be heated to a much greater temperature.

An example of the type of CPU fan which can be used to drive air through a solar heater

A PV Electric Solar Panel could be used to power a small fan (such as that used to cool the processor in a computer) to drive air through the snake. The final temperature achieved would be lower, but having a large quantity of 30 degree Celcius air entering a room is much better than a much smaller quantity of 50 degree Celcius air.

Solar Heating Links

Instructions on building a similar Beer Can Solar Heater (4) are available on the Squidoo website. An alternative very simple but larger design is detailed on this instructables page: Solar Heater (5) - no cans required.

Web Link References

(1) http://www.reuk.co.uk/Introduction-to-Solar-Water-Heating.htm
(2) http://www.reuk.co.uk/DIY-Solar-Water-Heating.htm
(3) http://blog.hemmings.com/index.php/2007/04/26/almost-free-garage-heat-just-drink-a-lot-of-soda/
(4) http://www.squidoo.com/beercansolarheater
(5) http://www.instructables.com/id/EMU06ULZ1MEY95WRNU/