IMPERIAL UNITS (UNITED STATES)
So let’s say there is a wall that contains R-10 insulation, and the wall measures 8 feet high by 10 feet long, or 80 square feet. It is 70°F indoors and 30°F outdoors, or a 40°F temperature difference. The calculation looks like this:
80 square feet * 40°F difference / 10 (R-10 insulation) = 320 BTU’s
METRIC UNITS (CANADA EUROPEAN UNION)
Calculation shown using °C, meters, SI R-values and watts.
Let’s say there is a wall 2.4 meters high and 3 meters wide (7.2 square meters). The outside temperature is -1 °C, while the inside temperature is 21° C (22°C temperature difference), and the insulation is SI R-1.8. The calculation looks like this:
7.2 square meters * 22°C difference / 1.8 (SI R-1.8) = 88 watts
(If you multiply watts by 3.4 you get approximate BTU’s)
In other words, you would need a heater producing 320 BTU’s to compensate for the heat loss through that wall, and that heater would be running continuously.
BEE COZY ON A BEEHIVE EXAMPLE
A standard Langstroth beehive is 0.23 square meters and the outside ambient temperature is -30ºC (-22ºF) while the cluster inside the hive is working to keep the temperature at a balmy 27°C (81ºF). The outside vs. inside temperature difference is 57. A Bee Cozy Winter Hive Wrap contains SI R-1.4 (R-8) insulation and a beehive has approximately SI R-0.13 (R-0.71)1. The equation looks like:
0.23 x 57 / (1.4 + 0.13) = 8.6 watts
(If you multiply watts by 3.4 you get approximate BTU’s and vice-versa)
In other words, you would need a heater producing, or the bees will need to work to heat the hive, 29 BTU’s to compensate for the heat loss through the walls.
Whereas if there is no insulation on the beehives, the bees will need to work to compensate for 343 BTU’s.