Also in Chicago, and last night was -2F. I have 3 Easter egger bantams who have never had any eggs yet, they are about 6months old now. No heat in my plywood coop. Just pine shavings and hay. Heated dog waterer was able to keep water unfrozen all night. I left the coop windows cracked open for ventilation. Give my chickens extra mealworms and scratch before bed. This morning I opened the coop door and they were alive standing on their roost. They seemed OK. Hope it gets warmer though, I know they have been spending most of the day inside the coop even though their run has hay and clear tarps for wind blocks.