The efficiency of a furnace is measured in a rating known as AFUE (Annual Fuel Utilization Efficiency). A lot like your car’s miles per gallon rating, AFUE tells you how efficiently the furnace converts fuel (gas or oil) into heat. An AFUE of 80% means that 80% of the fuel is used to heat your home, while the other 20% basically goes up the chimney.
The government mandated a minimum AFUE rating for furnaces installed in new homes is 80%. (In contrast, many furnaces manufactured before 1992 had AFUE ratings as low as 60% â€” so nearly half the fuel was being wasted.) Furnaces with AFUE ratings of 80% are considered “standard”; those with ratings of 90% or higher are known as “high efficiency.” The maximum furnace efficiency available is around 96.6%.
In general, a higher efficiency furnace usually means two things:
- higher price
- lower monthly operating cost
If you have an older furnace (with an AFUE of about 60%), you could save up to 60% on your heating bills by replacing it with a new high-efficiency furnace. So the cost to replace your old, inefficient furnace is paid back through lower utility bills.