SEER Rating: SEER stands for the Seasonal Energy Efficiency Ratio of an air conditioner or heat pump. It measures the amount of energy used over a typical cooling season. The higher the number, the more energy efficient the unit.

AFUE Rating: AFUE stands for Annual Fuel Utilization Efficiency, and it measures furnace efficiency. A higher AFUE means a more efficient furnace. The U.S. government stipulates a minimum AFUE of 78 percent for all gas and oil furnaces.

HSPF Rating: HSPF is the abbreviation for the Heating Seasonal Performance Factor. The HSPF number identifies the heating efficiency of a heat pump. The higher the HSPF number, the more efficient the heating performance of the heat pump.