The seasonal energy efficiency ratio (SEER) is a measure of the seasonal or annual efficiency of a central air conditioner or air conditioning heat pump. SEER takes into account the variations in temperature that can occur within a season and is the average number of BTU (British thermal units) of cooling delivered for every watt-hour of electricity used by the heat pump over a cooling season. It is determined using specified federal test procedures. The higher the SEER, the more efficient the unit and the lower the operating cost.