In Huber's New Observations Upon Bees, there is a chapter on ventilation that every beekeeper should read. Ventilation is neither as complicated nor as simple as you might expect. Bees accomplish a lot with only one small opening and often accomplish less with multiple openings.
"Fourth Experiment. Same as Third, But Two Candles.
I wished to see whether my ventilator would provide enough air for two lighted candles. They burnt for 15 minutes and then went out together. In another test where the mill had not been started they burned for 3 minutes only.
"Fifth Experiment. Increase in Number of Openings Decreased Actual Ventilation.
We tried increasing the number of openings in the side of the box, but were not successful. One of the two candles went out at the end of 8 minutes. The other kept alight as long as the ventilator was in motion. I had therefore not obtained a stronger current by multiplying the openings.
"These experiments show that in a place with an opening only on one side, air can renew itself when there is some mechanical cause tending to displace it, and this seems to confirm our conjectures on the effect which the fanning of bees has on the hive."--Huber's New Observations on Bees Volume II Chapter 8
http://bushfarms.com/huber.htm