An air conditioner with a "seasonal energy efficiency ratio," or SEER, of 13 has a certain degree of efficiency in regards to its cooling output and energy input on an annual basis. Compared to a SEER 10 air conditioner, a SEER 13 air conditioner is 30 percent more energy-efficient.
A mandate by the U.S. federal government on January 2006 made SEER 13 the new minimum requirement for central air conditioning systems. Air conditioning equipment with higher SEER ratings are now available. Over the lifespan of an air conditioning system, a higher SEER rating typically results in lower operating costs and fewer greenhouse gases being released into the atmosphere.