When my chicks were 7 days old I put them in their coop with a heat lamp & a wire cage that I kept covered to keep the wind off of them. They haven't had heat for two weeks. They were completely feathered out at 4 weeks. I however do live in Texas. They went through some cold weather & did fine. They grew their feathers extremely fast & are very healthy. They now all roost at night & are 6 weeks old.
Here's a picture of them I think they were about 10 days old.