chicks in brooder and fresh air.

I've been reading a lot about the benefits and importance of making sure chickens get plenty of fresh air inside the coop, even having part of it open (screened) to promote air flow. We have good ventilation in the barn so I'm not worried about the adults, my question is about my brooding chicks. I have 15 of them ranging from 2-6 weeks and they are inside the house in the bathroom. It has gotten pretty stuffy I'm there with 2 heat lamps and 15 little chicky bodies warming up the room, so I cracked the window to give them some fresh winter air. Thoughts?