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. SEER ratings range from 13 SEER (which is the lowest possible efficiency air conditioner product that is manufactured - and thus is the unit which uses the most energy to operate) to over 20 SEER (the most efficient manufactured air conditioners which uses the least amount of energy).