A SEER (Seasonal Energy Efficiency Ratio) rating predicts your central AC, heat pump, or mini-split AC unit's energy input and output. It is calculated by taking the total cooling output and dividing it by the total energy input of an AC unit over one year. The higher an AC unit's SEER rating, the more energy-efficient it is. The Department of Energy (DOE) requires a minimum SEER rating of 13 for all AC units manufactured after 2005. Energy Star-labeled AC units also must have a SEER rating of at least 14 and utilize 8% less energy than other AC units.