I've noticed quite a few posts asking about heating the coop. Having recently discovered the beauty of rocket mass stoves, I quickly began brainstorming and connecting coops to this idea. Well, I live in North TX so we don't typically get cold enough to justify heating coops, but I might try something like this myself just for fun. The theory behind rocket mass stoves can be found in depth on youtube. But my thought is burying the duct work underground and use the ground as the thermal mass. I'm not sure how much heat would be generated, but I'm sure it would depend on the diameter of duct you use. I originally thought about using this method as a heat source for my greenhouse, and I still am... Just need to get a free 2 or 3 weekends to do it is the main hold back. I would love to have a greenhouse butted up to the coop and share a common heated cob wall that heated both coop and greenhouse. I'm sure it's doable, and I know lots of you are very handy, so get to work!