I didn't heat the coop. I put a brooder lamp with a 100 w bulb in it, which probably provided some nominal heat, but not a ton. My chickens did just fine. I did have a heated waterer though.
I also have the water warmed bowl. I use the heat lamp, but like Lisa, I leave the little pop door open..so..funny that this was brought up, because just today, I was in there watching one of my hens. I noticed that it was still quite cold in there, but the wind was really going, like usual in windy city here in the mornings. It's actually warmer at night when the wind isn't blowing so hard. I'm thinking just a light next year too. I like them laying through the winter.
