SEER (Seasonal Energy Efficiency Ratio) is a system for rating the efficiency of cooling equipment. The higher the SEER rating, the less your unit will cost to operate.
HSPF (Heating Seasonal Performance Factor) is a measurement similar to SEER, but it measures the efficiency of the heating portion of a heat pump.
Energy Efficiency Ratio (EER) This measures the cooling output of a unit divided by its total energy consumption, measured during continuous operation at a given operating condition (95 degrees or full load).
Integrated Energy Efficiency Ratio (IEER) This measure expresses cooling part-load EER efficiency for commercial unitary air conditioning and heat pump equipment on the basis of weighted operation at various load capacities.