Thought I would add my 2 cents. I hatched 7 chicks just before Thanksgiving, had a regular 75w bulb on them for about 2 weeks, the bathroom they are in stays 60-70 degrees. Took the bulb away as they were feathering nicely, then last weekend put them outside in a small run with a dog crate to huddle in at night. They are doing great, no huddling or acting cold,they are actively running around pen. My feelings are that we are creating non-hardy chicks and chickens by giving them too much heat too long. They are much more adaptable and hardier than people think. I have loved having chicks this time of year and they should lay late spring when people will just be getting their chicks. The Temps here have been 30-50 degrees, which I understand is a little warmer than where some of you are. My parents have both had chickens since they were kids and my dad is 83, he remembers the kerosene incubator his parents used when he was abot 6 yrs old.
Joy