I've slowly weaned them off the heat lamp and temps are in the 30s still here at night. I have one out there still just in case it goes lower and I see them piling. For now I have found a surprising substitute to the heat lamp....one very confused rooster.
My theory...and this is just a theory, mind you...is that I'd rather they put some of their energy right now into feather growth and maintaining warmth, while their bones are young and soft. They have plenty of time to pack on the weight when they aren't so young and they should have all their feathers grown by then. So right now we are at twice a day feedings, full on free range, fermented whole grains only and less heat at night. Will take it down to once a day feedings soon.