SEER (Seasonal Energy Efficiency Ratio) ratings gauge the efficiency of an A/C unit. Find out how to find your unit's SEER rating and what the best rating is. SEER is a central air conditioning unit’s Seasonal Energy Efficiency Rating. Unlike the EER (Energy Efficiency Rating), the SEER estimates a unit’s performance over an entire cooling season, rather than measuring its performance at a given temperature and humidity level. In short, it measures the seasonal performance of the unit based on the cooling accomplished (in BTUs of energy) divided by the electricity consumed (in kWh).