It would not let too much heat out if you opened quickly for a little peek. It might offer the reassurance you desire. coop needs windows! Both for ventilation and natural light.
So, here's the lyrics, or part of them
Little Green Apples
Roger Miller
And I wake up in the mornin'
With my hair down in my eyes and she says "Hi"
And I stumble to the breakfast table
While the kids are goin' off to school…goodbye
And she reaches out 'n' takes my hand
And squeezes it 'n' says...
They are 5 weeks old now. They are just fine. If you are concerned, you can build them a huddle box. But, adding heat at this time would be totally counterproductive.
Yes, they are 4 weeks now. So one more week of hardening off, out during the day, back in the house for nights, then out for good next weekend.
And this is for Chicken George and you. Enjoy!
During the next week, you can increase their outdoor time. By the time they are 4 - 5 weeks old, they should be good to live in their permanent coop/run without heat with outdoor temps between 30 and 70*. If you are concerned about them moving outside, you can build them a huddle box.