Just thought I would share with you what I am trying for a little warmth for my chickens this winter. I built a heater out of an old window and 30 aluminum cans. I just stacked up cans with holes drilled in them to allow the heat to rise thru them when the sun hits them and painted them flat black and siliconed them together. It took me about 2 hours worht of time so if it does not work I am not really out anything. I will update how it is working once winter gets here.Started out with an old window and some aluminum cans. drilled a hole in the side of the bottom row of cans and then a hole in the bottom of the rest for the heated air to flow thru Measured and cut holes in the coop wall, lower to pull air in form the coop and the upper to allow the heated air to return into the coop siliconed the can stacks together and painted them flat black to absorb the heat from the sun here is a view of the openings from the inside of the coop the install is complete view of my coop ( old ice fishing shack) , c'mon sun heat the cans.