I think the ventilation comes via the large front "windows" and then up and out the top windows. I would expect that the birds create heat currents asthey heat up the air around them. THere would be some loss via the body and some via the breathing. Since warm air rises, I bet there is more air moing in to replace it. I expect the coop would be colder than some of the cooops I have now. But in a healthy way.
Will be interesting to see if Jack has other thoughts/ideas.
Q--- how many birdscan live in a 10 x 16 unti as the coop, not the run?? haven't found that info yet.