I was just winter using my coop, and put duct tape and cardboard over the vents. I guess that was the wrong thing to do. I did notice it was really humid inside yesterday. I might drill some smaller vents, since my vents are big doors at the top on each side. I would think bottom venting would keep the heat from rising out. Or should I just not insulate the existing vents at the top, and keep them closed?
Actually, you WANT the hot air to leave, the warm air is the wet air, it's better for that hot wet air to get out so that drier (and yes, cooler) air can come in. Chickens are well equipped for cold, but not cold and wet. Moist air will just get them cold faster, like stepping out of the shower into a cold room what felt just fine and warm enough before you got yourself wet.