Yeah you are going to get a lot of different answers. You’ll even get different answers from me depending on circumstances. Instead of telling you what to do, I’ll tell you some of the things I’ve done.
First of all, my brooder is in the coop. I agree you have to be real careful of fire danger, but that’s true in your house too. My brooder is fairly big, 3’ x 6’, and well ventilated. I keep one area warm and let the rest cool off as it will. That way they can find their own comfort zone. What happens is that they play all over that brooder and go back to the heat when they need to warm up. That way they get acclimated to the cooler temperatures, just like they do when a broody raises them.
In colder weather I’ve kept them in the brooder under heat day and night for 5 weeks, in really cold weather when it is below freezing maybe a few days longer. In the heat of summer I’ve turned the daytime heat off at 2 days and the overnight heat off at 5 days. That’s days, not weeks.
I’ve put 5 week olds in my grow-put coop when the overnight lows were in the mid 40’s Fahrenheit. Just a few days later, when they were 5-1/2 weeks old, the overnight low hit the mid 20’s. They were fine. My grow-out coop does not have any heat source but it does have real good draft protection. It’s also well ventilated up high.
I have regular full-sized breeds, not the Silkies or other ornamental breeds and not bantams. I don’t know if that makes a difference or not since I don’t have any experience with them.
We’ve all got unique circumstances, not just weather but different breeds, different coops, different risk tolerances, different experience levels. What works for me in November does not work for me in July. There is no one magic age that works for all of us regardless of conditions or circumstance.
