SEER is a type of rating system for Air Conditioners. It stands for Seasonal Energy Efficiency Ratio. Think of it like gas mileage, the higher the number, the less electricity used while delivering the same cooling. Most A/Cs installed before 2009 are 10 S.E.E.R., after that the government mandated a minimum of 13 S.E.E.R. While Carrier offers units well over 21 SEER, our cooling season is so short upgrading that high may not be warranted. A lot of homeowners are choosing 15-17 S.E.E.R. and are able to take advantage of rebates from ComED.