I've got 10 Gold Star layer chicks in a 4' X 8' well insulated, draft-free coop in Zone 3 (northern Wisconsin). I started the chicks late in the season. They are now 9 weeks old. I've obviously been heating the coop up to this point. Outdoor temps have been down to 20 degrees F. at night. Most recently I've had a single red heat lamp running, with the thermometer on the floor reading about 45 degrees on the worst nights. (It's much warmer up near the roosts, but they aren't all roosting yet!) I'm wondering when the chicks would be sufficiently feathered out to be comfortable without supplemental heat. Any rules of thumb as to when a hen is "fully feathered?"