People tend to anthropomorphize their animals (especially pets). Your chickens are a lot tougher than you dealing with the cold. The heat and humidity here in north Texas are far more dangerous to them than our mild winters. They do not need to "acclimate". They are wearing a full body down coat.
Beth, your chickens will be fine. no need for heat lamps. There are folks from Canada on this forum who do not heat their coops in any way. As long as they are not out in the open with winds blowing right on them they will be fine.