What is EER.? E.E.R is short for energy efficiency ratio. This method of rating air conditioning efficiency was introduced in 1975 by the Air Conditioning and Refrigeration institute (ARI).
EER is the cooling capacity of the air conditioning system in btu’s (British Thermal Units) divided by the power consumption in watts.
A 2 ton system is 24000 btu’s (12000 btu per ton)
If this system were using 2500 watts
24000 btu / 2500 watts = EER 9.6
EER is a measurement of a system running under specific conditions and does not take into account such things as seasonal changes in performance, system cycling etc..
SEER (Seasonal Energy Efficiency Ratio) is the more commonly used residential air conditioning efficiency rating these days. For a reasons I don’t agree with certain EER ratings are still a requirement for some tax credit and rebate programs.