I'm sure the first thing you noticed is the huge difference in annual heating costs between a tuned up furnace running at 80% efficiency and a neglected or worn out furnace operating at only 65%.
If you don't know the efficiency of your heating plant, call the folks who service it to find out how efficient it's running. If your furnace or boiler hasn't been given the once-over in a while, now would be the perfect time to find out how efficiently your heating dollars are being spent.
Generally speaking, if your furnace or boiler is more than 15 years old you should consider replacing it with one of the newer high efficency units. If you have yet to take advantage of the Federal incentives for energy efficient appliances you are still elegible for up to $500 in tax credits.
* Fuel costs per unit are taken from the Fuel Comparison Chart on this site. ** Fuel Consumed is based on 90 Mil BTU; the approximate number of BTUs needed to heat a 1,800 -2,000 sq. ft. home for one heating season in the Northeast including hot water. The exceptions to this are corn, wood, and wood pellet stoves which provide supplemental heat and no hot water.