> What is too much ventilation? How is that defined for you? Does anyone use
> screened boards (open) with a top entrances in winter in non-insulated
> hives (not recommended in my humble opinion)?

Every year about this time the topic rolls around to wintering. This has been researched, debated, concluded, and revisited. Personally, I think screened bottom boards were a bad idea in the first place and see no good come from them. 

¶

Effects of Entrance Location on Cluster 

The bottom entrances were closed and the top entrances remained open on all colonies for a few days and then the openings were reversed. The bottom entrance had no effect on the reaction of the cluster because of temperature. Nor did the bottom entrance affect the temperature in the bottom body of the check or packed colonies. When the top entrance was closed, the cluster moved closer to it and did not draw back at night as it did when it was opened. Except for temperature changes caused by the cluster movement, the temperature distribution in the hives was not altered by changing the entrances.

Although the effects of the outside temperature on the cluster were reduced when the top entrance was closed, the bees were prevented from leaving the hive on warm days. Periodical bee flights in winter seem to make for a healthier colony. Without an upper entrance the bees were confined to the hive most of the winter and thus their chance for winter survival possibly was decreased. The lower body of the check and packed hives never warmed up enough to permit the bees to fly from the bottom entrance.

• The temperature within the cluster varies, but under normal conditions it is not closely correlated with outside temperatures. However, a pronounced change in the temperature during the day will cause an appreciable change in the cluster size and temperature.

• Honey bees make no attempt to maintain the temperature in the domicile outside the winter cluster. 

• Under normal winter conditions either insulated or non-insulated colonies should survive at Madison, Wis.

The Thermology of Wintering Honey Bee Colonies, CHARLES D. OWENS. Agricultural Engineering Research Division, 1971

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