The efficiency of gas and oil furnaces 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 90% means that 90% of the fuel is used to heat your home, while the other 10% basically goes up the chimney.

In 1992, the U.S. government established a minimum AFUE rating for furnaces installed in new homes at 78%. (In contrast, many furnaces manufactured before 1992 had AFUE ratings as low as 60% &151 – so nearly half the fuel was being wasted.) Furnaces with AFUE ratings of 78% to 80% are considered “mid- efficiency”; those with ratings of 90% or higher are known as “high-efficiency.” The maximum furnace efficiency available is around 96.6%.

The cooling efficiency for air conditioners and heat pumps is measured in a rating known as SEER (Seasonal Energy Efficiency Ratio). The higher the number, the greater the efficiency.

The typical SEER rating of units manufactured prior to 1992 is about 6.0. In 1992, the government established the minimum cooling efficiency standard for units installed in new homes at 10 SEER. High-efficiency units have a SEER of at least 12.0; the maximum available is about 17.

Heat pumps also have heating efficiency ratings, indicated as an HSPF (Heating Seasonal Performance Factor). In general, the higher the HSPF rating, the less electricity the unit will use to heat your home.

The 1992 government minimum heating efficiency standards for new heat pumps is 6.8 HSPF. Most heat pumps manufactured before 1992 have HSPF ratings below 5.0. Today, an HSPF of 7.5 or higher is considered “high-efficiency”; the maximum available is 10.