When we got our chicks, it was still cold outside and our pig started nesting so we gave her the heat lamp in case she had her babies on a cold night. Our chicks did fine in our spare bathroom from a little over a week old with no heat lamp. We just kept the door closed and turned up the heat in the house a little and that bathroom stayed much warmer than the rest of the house, around 78-80 degrees. They weren't acting cold (they weren't huddled together in a ball, they bounced around peeping and eating just fine). We moved them outdoors before they were fully feathered. They had outgrown their cage in the bathroom and had started growing their feathers. I'm in south georgia. So it was already in the 70s and 80s during the day and the 60s at night. We built a little temporary pen and kept a heat lamp for them outside and left the door to the pen cracked so they could go in and out as they pleased. When they moved out of their pen and stopped sleeping under the heat lamp we just turned it off. That was about the time they were fully feathered.
I don't know much about keeping chickens in a colder climate. I just know if they aren't staying under the heat lamp, or sleeping under it, they don't need it. Just keep moving the heat lamp up, and if they start acting cold move it back down a little. That way you can slowly get them used to lower temperatures. When you move them outside just make sure they have access to a heat lamp near their food and water in a place that will block the wind so it's easy for them to find it. If they are cold they will use it and stay under it.