Some of you will probably laugh at me but I put out a heat lamp the other day when we went from the 70's to the low twenties in one day. Here, the worst it ever gets would be to go down to 15. But I did see that they didn't seem to care about the low twenties. If they were cold, they would have huddled near the lamp but they weren't.
My coop connects to an enclosed run and so it's the run that I lock up to keep predators out. Anyway, the coop doesn't have a door so they go out to the run whenever they wake up (and so I don't have to get up). That morning, they were down in the run not giving a crap about 23 degrees and these are birds that live in Texas! The run is covered in sand and I wondered if I should put hay down, but they didn't seem to care.
So, I learned I don't need to worry so much about them in the cold. I just put an aquarium heater in their water to keep it from freezing and won't worry. I do need to work on some wind blocks for the run for when fronts come through.
I think people should take care of their chickens how they see fit. If they want to provide heat, fine. I know I slept better. I did learn that my birds didn't need it in the temps I get here. If they were going through a hard molt and a front like that came through, I'd probably stick a lamp out there again.