heat pump back-up problems

[kiwimisterweewee]

I'm new to this so please exuse me if I'm not doing this right. I live in Pacific north west area and got a heat pump last may/08. I have an oil furnace back-up. This past winter the back up never came on until the temp got to about minus 6 c or 7. Now the back up comes on even when the temp is only minus 1 or 2. The only differance is we have had a week of fog....will this make a differance?