How much heating oil does it take to heat your house?

My house is 2600sq ft in size and i have worked out that the oil burner is using about 2 gallon (9 ltrs) of oil every day and that is only with the heat being on from 5 to 10 at night.This is a new house so should be well insulated and has double glazing. The boiler has not been serviced since we moved in which was 7 years ago so could this be part off the problem? How much oil do you use at this time of the year and what size is the property i just want a rough idea so i can compare with it.