I have a Lennox X15 heat pump and due to the lower electrical cost on my dual energy plan, it appears to be saving me a fair bit of money, while also providing A/C in the summer months. However, this year, I feel that my oil furnace is kicking in more often than it did last winter (about once / hour with an outside temp. of -8 C.). Of course, at -12 C. or below, only the oil furnace will operate. How often should I expect the oil furnace to operate when the outside temp. is in the -8 to -10 C range? My house was built in the 60s, and is insulated with 4" rockwool in the walls, and 12" of fibreglass in the attic.