I just wanted to remind everyone, that not all states, or climates are the same. The Mid-West is much dryer as is Alaska than the Northern East Coast. We get the lake affect, as well as the weather off the ocean and have had VERY high humidity this year. It is NOT the cold that can hurt or kill them, it is the humidity. When the outside humidity is as high, or higher, than inside the coop, there are problems...we have had both this year. High High humidity and the frigid cold. I lived in MN for years, and even though it is colder than here, it was dryer and didn't feel as cold. Had I had chickens in MN, even when it was MUCH colder than here, I doubt I would have needed to add any heat. With the darn high humidity this year, even though we are only getting -20 pretty consistently and some -30 degree temps, combined with the 104% humidity, well, I put in a heat lamp. The birds were not comfortable and with the prolonged frigid temps and high humidity, I have changed my outlook on adding heat. Not above freezing...see my above post...but there are areas, in the county, that if we followed the "rules" we WOULD be losing birds. I have read of people losing birds around here also this winter. One person lost their whole flock. They went out in the morning and the flock was frozen, literally.
 
Yes, birds can take low temps, and temp extremes ok, but add that humidity and there is trouble.
 
 
 
I don't heat the coop unless the humidity AND the cold are going to be extreme. The birds tell me, very vocally, that they are not happy nor comfortable. I also don't advocate heating a coop above freezing, in the colder climates, BUT...if the birds are suffering, and like me, you are fighting a losing battle with the humidity outside the coop, it's time to rethink the "rules".