Adding heat has always been a controversial subject, some people are totally against adding heat, others use it regularly. It's definitely a personal decision. Adding heat does not necessarily equate to using a heat lamp, there are lots of other ways to heat a coop or a single bird that is totally safe and will not burn a coop down.
I have found in my flocks over the years there are definitely times when heat is needed. Chickens can and do indeed get cold at times, whether or not they need a heat relies intirely on our ability to decern their needs. Some flocks can tolerate frigid temps well below zero and others get chilled at 20F. Health and age of the flock plays a huge part as to how well they tolerate the cold. Sick birds can and do die in frigid cold temps.
I have rarely added heat to the entire coop all night long, even turning on a panel heater when it's -5F can have birds getting off the roost bars and seeking out cooler spots in the coop at night. A healthy bird can adapt to any environmental temp over time.
Very young birds, weak or sick birds, molting birds that are shivering and senior birds can all use a dose of heat at times, especially the senior birds. I have kept several birds aged well into their teens and I have learned that without heat, they will freeze to death and die. Like an old person, they lose muscle mass, muscles generate heat, old birds become quite thin. All my old birds starting around the age of 8 had to be watched, adding heat when temps were in the 20s. By the time they reached the age of 10, the temp tolerance was in the low 30s. Hens in their teens couldn't tolerate temps below 40F. Never ignore your senior birds, they need special attention as they age and adding heat will allow them to live a lot healthier and happier as they age.
