CLamb, adding your location to profile would help. Some places where furnace gets lots of use need annual inspection, a spring or summer inspection may be cheaper and easier to schedule than in busy heating season. The furnace itself should be included in inspection.
Other, warmer, places recommended inspection may be every two, three years. It depends on how much hot, acidic gas is going up flue, general condition of flue and furnace, how effectivly it burns oil, and even chemical composition of oil used.
[CENTER][FONT=Comic Sans MS]Measure twice, cut once.[/FONT][/CENTER]
[CENTER][FONT=Comic Sans MS]Look at the nail, not the hammer. Watch the fence, not the blade.[/FONT][/CENTER]
[CENTER][FONT=Comic Sans MS]If you hook your thumb over your belt you won't hit it with the hammer or leave it layin on the saw table.[/FONT][/CENTER]