While winter ventilation requirements fall under that "beekeeping is local" banner, it is one of those pesky questions that, after over 150 years of beekeeping in this locale (coastal PacNW ), remains unanswered, and therefore a perennial topic of discussion and disagreement amongst local beekeepers.

Two years ago BC beekeeper Rudi Peters presented to the BC Honey Producers Association on his experience studying overwintering practice, presentation and summaries here:
https://bchoneyproducers.ca/portfolio/rudi-peters-overwinter-hive-sensor-discoveries/
https://herewebee.wordpress.com/2017/03/14/snow-business/

Because I am often entering winter with smallish new queen colonies in which conservation of the heat rising off the cluster is important, I followed Rudi's advice and took away the winter upper entrance. I have had no problems with damp hive interiors: it appears the bees are very good at managing humidity and air currents in the hive, using a reduced lower front entrance, thanks to their useful little wings.

That fact is widely described in discussions on heating colonies to temperatures that will kill Varroa under cappings. They report that the bees do not tolerate this and fan very efficiently to defeat any attempts to heat brood frames to the required temperatures.

The Paradise EPS hives have no upper entrance at any time of year, and are widely used in Norway. No issues with condensation, probably due to the fact that as Rudi observed, an insulated inner cover does not present a cold surface on which moist air off the cluster will condense and drip down onto the bees.

Overwintering config is another aspect of basic practice that does not seem to garner research dollars. Alas.

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