I live in northern Ontario and its already been -1 here at night. I have a heat lamp in the coop and I went out in the middle of the night to check the temp and it said it was 10 C degrees in there. our winters are long and cold the norm temps here in winter are around -25 but we get a lot of -35 to -40 nights and some days when there is a cold snap. I worry about my chickens getting too cold and getting sick or dying. today it wasn't windy or super cold in fact it was sunny and warm most of the day and they went out. When should I worry about not letting them out in your opinion?? the coop is large 10x12 and its an in-barn coop, I haven't insulated it yet for winter but that is soon to be done.