IR temperature measurements started on 12-Nov-2017 without the Bee Cozy. See a previous post, bee respiration, for measurement method. On 2-Jan-2018, the 17.0°F outdoor temperature convinced me to add the Bee Cozy to two vertically stacked hives. Only the queen excluder portion of a cloake board separate these hives. 1 Bee Cozy is added to the bottom hive (4 boxes) and 2 overlapping Bee Cozys are added to the top hive (5 boxes). The Bee Cozy is designed for 10 frame equipment. So, the Bee Cozy easily slips over my 8 frame boxes and cloake board with no effort. This 2-Jan-2018 measurement point appears as a blue dot in the lower left corner of dots - Paver temperature equals 17.0°F and Top Vent temperature equals 31.0°F. On the graph, think of the horizontal axis as outdoor temperature and vertical axis as the bee respiration temperature.
All graph points lie above the green line (x= y) which is consistent with an active and alive hive. Blue dots are measurements without the Bee Cozy and trend beneath orange dots which are measurements with the Bee Cozy. Excluding a few points, the Bee Cozy consistently increases bee respiration (Top Vent) temperature.
Wondering why I went into winter with such a tall stack of boxes which requires step ladder beekeeping - there's no good reason other than lazy beekeeping.