I have had a cooIp in Massachusetts and now Nebraska. Both can et very cold. In Mass I had a small coop with 6 chickens (Rhode Island Reds - picked for their cold hardiness). I did some basic insulating in their coop and did not add any heat. I did have to hear the water so I got a heated dog watering bowl and their waterer sat right in it, and kept it from freezing. The did slow down in the egg laying category but still produced. I did check for them more regularly though so they didn't freeze. In Nebr their coop is the second half of a greenhouse, so the sun keeps it from freezing during day, and I have dozens of water bottles painted black to gather the heat during the day, and helps to add heat during the night, No other heat added, and no added heat for the water either. Again, production is lower, but still producing. Rhode Island Reds and Barred Rocks this time. They do come outside during the day, mine don't like to walk through too deep of snow, but will stay out for long periods. Enjoy your girls.