Lovely to know you are so caring for your chickens, Rick, but heating the coop really isn't a very good idea. Chickens are fantastically well insulated with duvet feathers and really don't need it, especially when temperatures are only marginally below freezing. If you raise the temperature in the coop, relative to what is outside, they will feel a big difference when they emerge in the morning - like you would, if you went outside from a warm bedroom in your pyjamas. Also, the temperature difference inside the coop may lead to condensation and damp, hence bronchial problems. It does help if you give them a warm mash of pellets and a bit of corn moistened with hot water before they go to roost, about 3.00, they will have full crops and be able to generate plenty of heat overnight for themselves. And get down there early in the morning with a fresh drinker of liquid water, of course. I think you can buy heating pads to go under drinkers, which could be useful for a techno chicken keeper who wants his birds to have all modern mod cons!
So long as they are dry and sheltered from direct wind inside, it's good to leave the ventilators open, and indeed I leave the pophole open all the time as well, and have never had any bronchial problems with any of my birds, over many years, Chickens manage cold temperatures much better than heat - when it comes to summer, they need help keeping cool.