Since January 2006, all residential air conditioners sold in the United States must have at least a 13 SEER. SEER is the abbreviation for Seasonal Energy Efficiency Ratio and it is a U.S. government standard energy rating and reflects the overall system efficiency of your cooling system. An EER is short for Energy Efficiency Ratio and doesn’t take into consideration the time of year, but rather the system’s energy efficiency at the peak operating use. Both ratings should be considered in choosing cooling products. The rating is a ratio of the cooling output divided by the power consumption and measures the cooling performance of the system. The Federal government developed an ENERGY STAR program for high efficiency central air conditioning systems that in order to qualify must have a SEER of at least 14.