Build Your Own Solar Furnace

Six shining soda can bottoms against a black background.
What You'll Need
50 empty aluminum soda cans
Wood glue
Adhesive caulk
Black spray paint
An old vacuum hose

Capture the energy of the sun with your own DIY solar furnace and help heat areas of your home for basically nothing. You can find many of the necessary materials lying about your home. You’ll save money, recycle some cans, warm up a room, and keep your environment a little greener. This is great for winter days that are both sunny and cold. When caulked, painted, and under plexiglass, it looks like a high-tech appliance and not a recycled project.

Step 1 - Collect and Prep 50 Cans

Depending on your rate of beverage consumption, this could be the most time-consuming part of the project. You need 50 empty, cleaned 12-ounce cans. The only requirement is that they all be stackable, so the bottoms all fit snugly on the tops. You're going to make five stacks, each with 10 cans. These cans act as the absorbing plate for your homemade solar furnace.

Once you’ve collected them all, thoroughly wash them so you don’t have to worry about any insects or gross smells. Then, drill a hole in the bottom of each can.

Step 2 - Make a Box

Now make a box using plywood for the back and 1x4 lumber for the sides. The size

Now make a box using plywood for the back and 1x4 lumber for the sides. The size of the box is dictated by the number of soda cans. A 12-ounce can is 4 3/4-inches high and 2 1/2-inches across. You’ll need two inches to the height of the box for air to circulate, so the box needs to be 49 1/2-inches high by 12 1/2-inches across.

Cut the plywood to that size, and then cut the 1x4s to fit the sides and top and bottom of the box. Glue 1x4s to the plywood and then screw them in place. You're using glue and screws because you want it to be both secure and airtight.

Step 3 - Caulk and Stack

After assembling the box, apply adhesive caulk to all the joints to keep air from escaping. Make sure to use a caulk rated for high heat, otherwise you could run into issues.

Stack the cans in the box, caulking them together as you go. Each stack of cans is a chimney, so you don't want air escaping as it travels up the flue, so make sure each can is sealed well to the next one in the stack. Allow the adhesive to dry before proceeding to paint them.

Step 4 - Drill Holes and Add Hose

Drilling through wood

At the top of the box, drill a hole to fit the vacuum hose you will insert here. These hoses are usually 1 1/2 to two inches in diameter, so make the hole whichever size you need. The hose will disperse the heated air from the absorption plate (soda cans). Make sure the hole is caulked around the hose and that the hose is anchored to the box.

Drill a hole through the base, matching up with the bottom of each stack. These will draw cool air inside.

Step 5 - Paint Everything Black

Once the adhesive dries, paint the cans and exposed surfaces of the interior of the box with black spray paint. Again, use a product rated for high heat. This helps absorb the sun’s energy. Paint the outside of the box too, to protect it from the elements.

Step 6 - Attach Plexiglass

A small rectangle of plexiglass

Cut a piece of plexiglass to the dimensions of the box to make a cover. Set it over the open side of the box and caulk and screw it into place. Make sure it's airtight.

Step 7 - Aim It at the Sun

Now that the solar furnace is complete, set it in a place where it will capture the most sunlight. Keep the base off the ground so it will let cool air in. As the air rises through the stacks, it heats up, gathers in the gap at the top of the stacks, and exits through the hose. Having it mobile allows it to be set in the best position which can help heat a portion of the home or possibly a small work space in a garage or shed. Set the other end of the hose wherever you want to feel the warmth. You may need to experiment with angling your new solar furnace to discover the best spot to capture the sun’s rays.