>My thoughts are that a bottom entrance as big as the top entrance should be ok for exchange of air. The incoming air will be colder, dryer, and condensed. The exhausting air, will have a higher RH, be warmer, and less condensed. Because of the coefficient of expansion of air as it warms, a smaller volume of air will enter then that which exits. How much air that enters the hive depends on how much air exits? The air will be pulled through the hive. 

The vent openings on my inner covers are widened to approximately 1 1/2 inch. The inner covers are placed with the thick rim side and vent opening down so there is about 3/8 inch of space between the inner cover surface and the tops of frames. Each winter I notice a few random colonies, less than 10%, reduce the top vent openings with propolis.

photo link: http://www.eccentricbeekeeper.com/imageshare/reducedentrance.jpg

There does not appear to be a common factor among the hives/colonies with reduced entrances. I have yet to observe a colony reduce the full width bottom entrance during winter.

Larry
Indiana

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