we have rather extreme cold, not normal for north Texas, currently 15 degrees F, wind chill about -4 F. I have chicks locked in coop with my old birds, and heat lamp on chick side of coop. Only drafts would be edges of east side and around door, top ventilation about 1 inch. They made it thru last night ok, I took hot mash (layer pellets and hot water) out for all of them this morning - 4 dishes of it, they have their Start n grow on their side of the coop divider by the heat lamp. I'm worried, temps will be about 13 degrees here again tonight, don't clear freezing until at least Friday noon I think. I know my chickens don't need that heat lamp, but the chicks are not that big. 6 weeks old and fully feathered. Lamp hangs from a chain far from the straw but low enough to heat their feeding area. Last night they perched on the lower 2 bars of perch near the light.