I wish I had stumbled upon this thread sooner! I raised my second batch of girls (12 black comets) in a brooder in my basement (heat lamp for first 4 weeks, then no supplemental heat). Now they are approx. 9 weeks old, and are going completely stir crazy!
I could use some advice at this point-
The new coop isn't finished yet, will probably be another two weeks or so. The weather here is still pretty chilly (today high of 39, overnight below freezing, but the next 10 days or so should be at or above 50 during the day, again with night temps in the 30's).
I have a space for them under my deck to use until the coop is ready, a decent sized run with perches, and a makeshift coop to protect them from the cold and to sleep. Since the birds are so big, using a MHP out there will only benefit one bird at a time, which won't necessarily do much overnight when they are trying to sleep, and the temps are at their coldest.
Will they need supplemental heat at this point, since they haven't really been "hardened off"? The basement is pretty consistently in the mid 60's, but on warmer days I have been leaving the door to the basement open to get some of the cooler air in there.