I’m well on my way to raising a second batch of chicks without any supplemental heat. I do provide a huddle that the can get under. This is lined with radiant foil insulation and when they all get together under it they are able to stay warm. However I am not doing this in subzero temperature and there is 37 chicks, enough to keep themselves warm.
They have moved outside at 10 days old into a dog kennel that I have put some metal roofing over. They are scratching away and being chickens. This is inside the electric fence to protect from predators.