I have 15 9 week old pullets in a insulated coop outside. I live in central Wisconsin where it can get very cold, especially at night. Some nights, not too many this year, it can go well below zero. I currently have 2 250 watt heat lights in there, but do turn off one when it gets nice. What I am wondering is, how long do I actually need to keep any heat in there on them? I want them to be as comfortable as necessary but would also like a lower electric bill ! Any one with any advice, thank you in advance!!