I have not made them myself but I did see a video of a guy that did it with beer cans. He built a 3x6 wooden frame and cut the top/bottom off of all of the cans then attached them with some sort of epoxy then painted it all black.
He also added a fan to the very end of the can-line to pull air from the heater into his shed. He said on a 20/F day the heat coming out of the rig was close to 104/F and could heat the whole shed without issue (I dont remember how large it was but it could not have been more than 160sqft.).
When I was growing up we had some very large solar heaters that were made out of black PVC and had water and a radiator with a fan to pass heat into a greenhouse. They worked fairly well and extended the growing season by a few months in a very cold climate. They were (if I remember properly) about 12ft long, 2ft deep and used at least 4" PVC in a large circulating loop.
The water solar heaters sound very effective. If it's possible to make them out of PVC I might have to look into that method. I assume they would require expensive copper, but if the PVC is painted black it makes sense that it would still capture plenty of heat anyway. I'll have to look into this system as well.
They worked out well enough. You can actually get black PVC that you wont have to paint. It was contained in a large "box" with one side being glass/plexi (that would probably cost the most). Ill try to find some links for how they were built. I was very young when my family was using them. This would have been back in the late 90's.
(post is archived)