I agree. Bees are very good at keeping themselves warm if they are healthy, well-fed and DRY. Of course the colder it is the more stressful it is for them, and otherwise marginal hives might not be able to withstand the additional challenge. The research seems to indicate that about 40 degrees is the ‘ideal” temp for efficiency of stores. Any colder and they require more honey to stay warm; any warmer and they risk becoming active and also consume more honey. Because of this it’s presumed that it’s the ideal temp for overwintering and is likely the gentlest temp, leading to survival of the most marginal hives.
Of course one downside of keeping your bees in a shed, is that thy can’t make cleansing flights. Personally, I would rather have my bees face some cold temps but also enjoy some cleansing flights when we get a few nice days. Having the best of both worlds like Joe sounds great.
Of course there is also a lower limit to the size a cluster can be. As with anything the larger the mass, the smaller percentage that is on the exposed perimeter of the cluster. If you get too small there simply aren’t enough bees to keep themselves warm and fed if it gets cold or stays cold for too long. Taking it to extremes, it’s obvious a cluster of a hundred bees, for example, wouldn’t be viable. I expect you’ll find, Trever, that one and two frame hives won’t do well, but I’ve never tried anything smaller than 5 over 5; I shied away from it when I heard others fail with 5 frames. I’m interested to see what you find. I’m surprised with your success with 5 frame hives, since I’ve never heard others succeed without using heat tape or placing on top of full hives for shared warmth. Do you put them above full hives, or warm/insulate them in any way? I would think it would be hard to have enough stores in this configuration while also having room for a viable cluster. I do agree that large clusters are not necessary, but they do provide a bit of extra leeway when Mother Nature brings her worst.
Of course there is also the question of what you want your hives to look like in the spring. If you overwintered a colony that is filling 3 deeps, you will be able to split it into a dozen hives (if it survives). If you overwintered those same bees in six 5 frame nucs, you won’t be splitting each of them more than in half. I know Trever prefers the latter, because it’s not an all or nothing proposition. You’re not risking all your survival and splits on one queen. I can definitely see advantages to either method.
Anyway, there are plenty of ways to keep bees and we’ve heard successes and failures of many different techniques. Please keep trying new things and report what you find. When possible try to be as precise in your observations as possible to help tease out what the important factors are. If possible, as Scott suggests, do side by side comparisons. While small sample size will mean it’s not a true experiment, it is the best we’re going to get.
PS, as Scott points out the UW experiment shows (and there have been others with thermometers placed at different places in the hive) the bees do not heat the hive; they heat the cluster. This is why I don’t advocate insulation. In my opinion insulation is more damaging by restricting ventilation than it could ever help by insulating.