What does your coop have for ventilation? It should have a window, and that window should be covered with hardware cloth to make it predator proof. As long as you've worked on weaning them from heat, they should be fine to move outdoors. My 4.5 week old chicks spent last night without extra heat. I moved them into the old coop, and there's a window at either end, adjacent to the 4' long perch. I did put them in a cat carrier instead of leaving them on top of the perch where they had settled, but tonight, I'm going to let them make their own choice. These chicks were raised with a heating pad, and it's the easiest batch I've ever raised. They moved outside with their HP at 1 week, and I moved an other batch of 1 week old chicks outside last night with their heating pad. Gotta love it. Check out Blooie's thread.