We are about 1.5 hrs SW of Pueblo at almost 8500 ft elevation (so colder weather than your area). I don't use a heat lamp. Instead I use a mamma heating pad and brood in the coop. I got chicks when they were 2 weeks old (had heat during this time.). Once at my house, they had the mamma heating pad for another two weeks. Since then, they have had no heat source. They are now 7 weeks old and doing great. Starting this week, I've been letting them out of the brooder so they can start integrating with the hens in the run. Today the chicks were confined to the brooder as it was snowing here.