Jay, in southern Ontario (Canada) wonders about wintering with screen bottoms.

I am near Albany, New York, where I suspect the winters are longer, if not colder, than in southern Ontario.  I winter with screen bottoms with no difficulty, and know another beekeeper (one of the best commercial operators around) who has done so for over 40 years!

As far as any drafts having any negative effect on the bees, recent studies have disproved the old myth about bees constantly rotating their position within the cluster.  Instead, bees maintain their position for several weeks, depending on how often a warm spell arrives.  Those on the outside of the cluster provide insulation and exist in a state of almost frozen...from which they readily recover.  Those on the inside generate heat and keep the cluster center at 90 degrees F.

My advice is save your effort, and bee disturbance, and keep the screens on all winter.

Lloyd
Lloyd Spear, Owner of Ross Rounds, Inc.
Manufacturer of round comb honey equipment and Sundance pollen traps