Either take them back or use them for brooding chicks. Your chickens are much better off in a well venilated, draft free coop. Heating the coop can be detrimental. If they're dependent on artificial heat and your power goes out, you have a bunch of chickens not adapted to cold weather. Going in and out can be uncomfortable for them, too. Imagine this. It's winter. You have on all of your cold-weather gear. You go outside and you're comfortable because you're dressed for the weather. Now come back in, but don't take off your coat, hat, gloves, scarf, ski pants or boots. Leave them on for a good hour or so. That's what it's like for your chickens. They can't take off their down coats. They are much more tolerant of cold than heat.