The SEER (seasonal energy efficiency ratio) is how the efficiency of your heating and cooling equipment is measured. The SEER is the amount of cooling your system will deliver per dollar spent on electricity, as compared to other systems. For example, a 3-ton unit may have a SEER efficiency rating of 13, 14, or 15. The higher the SEER the more efficient the system will be. The SEER rating of any given unit can range anywhere from 13 to 21.