It was -10 air temp here last night. I think the high here is only 4 degrees, ick! We have four 250 watt bulbs going, and that is just for the bottle calves. I have my husbands work lights as heat lamps in the coop. He adjusted the timer for me (I could never figure that darn thing out, lol!) so it comes on earlier in the evening, and stays on later in the morning.