Ok so I go out to check on my birds. I have a one piece coop with a run below it. All banked up with snow and a clear tarp around the "run" area. I check the temp outside on my phone and check the temp in the coop without any birds in it. There is no wind today. So I go out is 14F and the coop is cool. No chickens in it. And then later on I go out to put them to bed and there is no change in the weather other than it's dark outside and actually probably colder. But the coop is nice and warm. I have 4 chickens. Do they heat the coop to 68F nope but they do heat the coop. Maybe by 2-3 degrees.
Now I'm confused. I'm a bit south of you and it was 10 degrees at 5:30 this morning. Right now it's only 11. Right now 14 would be almost balmy. LOL! My coop when it's dark runs 10 to 15 degrees warmer than the outside temps. On sunny days the coop will warm up to 50 or 60 with the little door open and the run stays relatively warm all day. The coop is 8 x 10 and the run is 8 x 14 and I only have 6 chickens.