Baby chicks are now 7 weeks -9 weeks old. 7 wks are going out to the coop this week. It got down to 39 last night and the 9 weeks old were in the 2x4x2 coop with a light bulb on. Seemed to do fine Thinking it will get to 32 and below soon ...What temp is the lowest they can handle when a young age but have all their feathers without a heat source of some kind.?