I probably have the 2nd best insulated hives on this forum after Derekm, but I don’t quite agree with Derekm in this case. I have experimented with hives made from materials ranging from 19mm wood to 50mm of foam. By the time you get to 2” thick polystyrene (insulation board), a hive gets a little bulky. The big box stores in Michigan just carry up to 2” extruded foam board and cutting the foam that thick becomes a little more dangerous on the table saw IMO. So I stopped experimenting at 2” thick polystyrene. Still, 2” thick foam bee hives would probably classify as ‘super insulated.
Heat loss calculations do say that a heat source of 10 to 20 watts would maintain a temperature differential on the order of 30 to 40F with respect to the outside temp. HOWEVER the real variable here is the heat source; namely the bees. Turns out they don’t make many watts of heat if they’re not in cluster, not raising brood, or not aggravated. If you’ve ever watched bees in such a condition they just hang around on the frames and pretty much do nothing. Doing nothing generates very little watts.
So once the brooding stops in the late fall (Michigan), the watts of heat from the bees drop and even super insulated foam hives drop down to the 50F to 60F range and the bees go into a light cluster. Once they go into cluster, they do start generating a descent amount of watts again and since it doesn’t take many watts to keep a super insulated hive +30 to +40F above ambient, my hives tend to maintain a temp of between 45F and 60F all winter.
However once they stop brooding for the year, even the bees in my super insulated hives do drop back to a loose winter cluster. IMO the advantage of super insulation is it prevents the bees from being exposed to the really bitter cold night time temps.
