Al, I think the reason my vents seem to be working pretty well is that the top vents are on opposite sides of the coop, providing air to flow through the whole coop at the top, venting out all the bad air. So far, the humidity in the coop has never been above that of the outside air, and the smell that greets you when you open the door isn't offensive. But, I do agree, better to have a bit too much venting than too little. For some reason I've just managed to make it work with less.