I saw a smaller version of this instructable a while back: here. At the time I was volunteering with a local animal rescue center. We had just installed a new 20' x 40' wooden barn as an indoor recreational area for the animals, but as the shelter was off grid there was difficulty heating such a large space. I decided to upscale the idea and see if it would work for us.

For this instructable you will need:

8 x 4 sheet of 1/2" marine plywood, the marine ply allows the unit to be outdoors without the worry of delamination.
128 full size (500ml) beer cans.
1 sheet of 8 x 4 6mm laminated glass (please use laminated safety glass cut by a specialist glazier as glass cuts are nasty).
Lots of 3x2 timber.
2 x 4" dryer vent kits with ducts.
2 x 4" PC case fans.
1 x 15W solar panel.
Black Barbecue or oven paint (this is required for its resistance to the high temperatures inside the heater)
Assorted screws & high temperature sealant.

Step 1: Prepare the Cans

First let me warn against trying to make all the empty cans yourself, this much beer is not healthy!

We put out an appeal for empty, un-crushed and washed out beer cans.

Each can will form part of a hot air stack or chimney, for this wee need to allow for air flow. The easy part is to remove the pull tabs from the top of each can, next you will need to make a similar hole in the bottom of the can. I used a step drill to make a 20mm hole.

Cans are designed to stack so this part is easy, I placed one can on top of the other and used some sealant as both a glue and a method to keep the hot air in.

I needed to leave space on the 8 x 4 sheet for a collection area above and below the cans so I limited my stacks to 8 cans high and the best fit for the sheet was 16 stacks wide.

Step 2: Prepare the Housing

Unfortunately my camera ran out of power so I have no photographs of this section.

Make a frame around the edge of the 8 x 4 using the 3 x 2 timer (mounted with the 3" as the upright)

Also make a retaining bar for the cans at the top and the bottom of the stacks, each of the retaining bars will need a 40mm hole drilled corresponding to the stack above or below, this will let the air through.

Finally drill a 100 mm (4") hole in the top and bottom collector areas, your vents will fit here later.

Step 3: Finish the Heater

Once all of the timbers are in place and the holes drilled, insert the stacks into the chamber and paint the whole inside of the unit black with the barbecue paint, the black paint will allow the unit to absorb more heat (rather than reflecting it, also the thin walls of the cans allow for a very fast heat transfer).

For my unit I wanted to have a degree of control over the heat passing through the unit, I had read that the heaters are quite efficient even on relatively overcast days so I decided I didn't want lots of heat on already hot days.

To prevent this I fitted 2 x 4" PC case fans and a small 15W solar panel, there are no fancy electronics here just the principle that the more sun light the hits the solar panel, the more power is generated and the faster the fans blow, the faster the fans blow the less time the air has to heat up in the unit and hey presto less heat on an already hot day!

Finally mount the glass, I had this predrilled by my glazier as drilling glass is a dangerous business and I'm not set up for that. Before I locked the glass down I gave the inside a good clean (as access is no longer an option and sealed the glass to the frame with the high temperature sealant.

Step 4: Mounting

The heater is great but at the moment its just a big hot lump of parts. I decided to mount it on a free standing frame (other instructables mount directly to the wall). I obviously wanted the unit to be as efficient as possible so I placed it on the south face of the barn and after a quick check for my latitude (Dublin, Ireland) it found that 35 degrees is the optimum angle for a solar panel (this goes for air and water heaters as well as PV cells)

I drilled corresponding 4" holes in the barn and mounted the dryer ducts. The duct on the bottom draws cold air from near the floor and pulls it into the unit, the air heats in the stacks and blows back into the barn near the ceiling, I know this means I am heating the highest space first but the building has a low 6' 6" ceiling height, also the air coming from the unit is about 15 degrees C hotter than it went in from the bottom.

I fitted the one way louvered vent on the top duct, this means that hot air can blow in on a cold day but it doesn't get drawn back out on a cold night when the heater is not working.