Nyna and Chirpy-
I know CO has many days of sunshine each winter; not so sure about Montana.
I have posted on other occasions about solar coops. If you have good southern windows, your coops can gain a lot of heat on sunny days. I had insulated shutters that I closed over the windows at night, to help keep the heat in. That's the big question: how to keep all that wonderful daytime heat from escaping at night?
Thermal mass is the answer. You insulate the OUTSIDE of the coop (blueboard is best) and add mass to the inside. Adding a double thickness of sheetrock is one easy way to do so. Another easy way is to add a few (2-3) dark-colored 30 gallon trash cans of water in a place where the sun will hit them most of the day. Or, if you don't get regular sunny days, use smaller, one-gallon containers. For years in Indiana, I had cold frames and lined the north wall with one-gallon milk jugs which I had painted black. I never had supplemental heat in those cold frames, and the only time I ever had a freezing problem was one two-week cloudy spell with temps going into the negative teens every night.
If those kinds of ideas interest you, search "solar greenhouse" on the internet, and you'll find more.
I have also kept an active compost bin in my greenhouse before, just for the heat it gave off. I think the hens might go crazy on it, but its something to thing about, too!