The efficiency of a furnace is measured in a rating known as A.F.U.E. (Annual Fuel Utilization Efficiency). A lot like your car’s miles per gallon rating, A.F.U.E. tells you how efficiently the furnace converts fuel (gas, oil or propane) into heat. An A.F.U.E. of 80% means that 80% of the fuel is used to heat your home, while the other 20% basically goes up the chimney. In 1992, the government mandated a minimum A.F.U.E. rating of 78% for furnaces installed in new homes. (In contrast, many furnaces manufactured before 1992 had A.F.U.E. ratings as low as 60% — so nearly half the fuel was being wasted.) Furnaces with A.F.U.E. ratings of 78% to 80% are considered “mid-efficiency”, while those with ratings of 90% or higher are termed “high efficiency”. In general, a higher efficiency furnace usually means two things:

  • lower monthly operating costs
  • higher comfort levels

If you have an older furnace (10-15 years old with an estimated A.F.U.E. of around 60%), you could save up to 40% on your heating bills by replacing it with a new high-efficiency furnace. So the cost to replace your older, inefficient furnace is paid back through lower utility bills.”