I’m wintering 5 frame double decker nucs and some 8 frame single nucs this winter. The 8 frame nucs didn’t build up quite as fast as I hoped in October so they’re probably only about 4 frames of bees at this point. So far both single story and doubles are wintering about equally well, but we have had a mild winter.
From a time management perspective, so far I prefer the single story nucs. They take a little less time to analyze and balance out when compared to the double deckers. The advantage of the double deckers would seem to be a potentially warmer heat bubble at the top of the second story. However that can be mitigated if the bees don’t have time to finish filling the second story combs with stores.
My nucs are currently using a bottom entrance and a rather small top vent. For my double decker medium nucs (next winter) I’m going to try Derekm’s heat bubble approach. No top vents, but with some breather holes on the bottom of the nucs for air exchange. Theoretically that would eliminate the chimney effect of heat escaping out the top.