In HVAC, SEER stands for Seasonal Energy Efficiency Ratio, which is a rating system of an air conditioners cooling capacity to power input. It is a measure of how energy efficient an air conditioning system is, and the higher the SEER rating, the more efficient the system is. The SEER rating is calculated by dividing the cooling output of the system during a typical cooling season by the power input. The SEER rating represents the potential efficiency of the unit under perfect conditions, but much of the system’s efficiency depends on the right sizing of the unit for your home, correct installation, and evaluation of other factors as well. The SEER rating is a maximum efficiency rating, and it is a good balance between the upfront cost of the unit and the amount you’ll save on your utility bills to choose a unit with a SEER rating between 15 and 18.