CEER stands for Combined Energy Efficiency Ratio and is most typically associated with room air conditioner or window air conditioner HVAC units. CEER measures the combined efficiency of the unit when it is in standby and when it's actually cooling a space. It is the ratio of measured cooling output (in BTU per hour) to measured average electrical energy input (in Watts) and measured standby/off-mode power consumption (in Watts).

As of June 1, 2014, CEER became the required means of measurement to certify room air conditioners with Energy Star. EER requirements were used in the Energy Star certification for room air conditioners prior to June 1, 2014.

More information on the certification change can be found in 10 CFR 430, Subpart B, Appendix F.