<<Re. The other interesting idea often discussed is that winter sunshine on the box surface heats the inside of the colony.  I often get that argument from folks that wrap colonies with tar paper thinking they get a net solar gain because the surface of the tar paper feels hot.  Does someone have data on this? >>

The following hardly constitutes “data” but I’ll offer it up anyway.  I note that much has been written about the benefits of plastic hive cozies, but I eschew them.  

During winter-spring 2019 I overwintered 12 colonies in my Portland, Bonavista Bay (Newfoundland), apiary. Six were wrapped with roofing felt, while six were wrapped with plastic cozies. The insulation in three of these cozies was water saturated presumably because water entered through staple holes in the plastic. 

I measured the temperatures inside these two types of wrapping but unfortunately for one day only. I’d like to do this systematically with a large number of hives. You can see from the appended table that there was a significant difference in temps between the roofing felt and plastic cozy wrappings.

Method:

Shoved a digital poultry thermometer (temp probe is on a long metal wire) in under the roofing felt or the black plastic wrap (inside the cozy) and waited a couple of minutes for the temperature reading to stabilize.  The probe was situated in the middle of the second (top) deep, on top of the wood outer surface of the deep.

Ambient apiary air temperature was +4.5 deg. C. Weak sunshine, thin overcast. All hives were sun exposed.  Gusts of breeze periodically.   Colonies in hives 1-6 had a few bees flying while none of the colonies in hives 7-12 were flying.

Hive entrances faced slightly southeast. Apiary is fenced for protection. Hives are warm configuration with 7” wide entrance reducers in bottom entrances and ½-3/4” wide upper entrances located in the inner covers (crown board).  Pink fibreglass house insulation used in vent boxes above ventilated inner covers.

BTW I have had zero winter-spring losses in 5 consecutive seasons (touch wood) using roofing felt (+ much more, e.g., we are Varroa-free in Newfoundland).  Obviously my colony numbers are too small to say anything meaningful about this...
 


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