Hmmmm....an insulated (various materials to use for insulation) 5 gallon bucket with horizontal nipples instead of the vertical ones. Set the bucket on a couple cinder blocks with the holes in the blocks up. You'll get a bit of heat from the ground if your blocks are on straw or shaving type bedding. If you top off your bucket with hot water in the morning, it won't freeze down to the bottom if you have circulation and your lows only get to 10. We get temperatures below zero during the worst part of winter. In my polish pen, I have a 2 quart container with the horizontal nipples. It sits on a cinder block upon which I put one of those seedling heat mats. At 18 below zero outside (I'm not sure of the temp in the coop) that little bottle never froze.
