I have 13 chickens, larger breeds in a green house about 5'X8'. It is a hard framed green house. This is their actual coop, no vegetation inside, it has worked out great so far, they've been in it since may/june. They have an enclosed larger outside run. I am wondering about whether or not they will be warm enough in the winter? Any ideas, about using a green house, this is our first year with chickens..