Take a look at your power bill and see what your total khw (kilowatt hour) useage was for the month with the Cary SLI-80 used. Compare the bill with the month before, or a couple of months before. Also check the number of days in the billing cycle. Chances are your utility company's "Energy charge", per khw, was higher for the month the bill was higher.
Also depending where you live colder weather, even with gas heat, the furnace motor runs longer and more often. That will increase the kwh useage.
Also depending where you live colder weather, even with gas heat, the furnace motor runs longer and more often. That will increase the kwh useage.