Energy Efficient Ratio (EER)The EER or Energy Efficiency Ratio measures the cooling efficiency of an air conditioner or HVAC system, determined by comparing the energy output to the energy input of a unit. Combined Energy Efficient Ratio (CEER)You might also see a CEER rating, or Combined Energy Efficiency Ratio, on your window air conditioner. Along with a variety of energy efficiency ratings set by the Environmental Protection Agency and the Department of Energy, Energy Star is a voluntary program for manufacturers and businesses that is administered by the EPA. Energy Star certification can apply to anything from a window air conditioner to a dishwasher or washer and dryer. Energy-Efficient Air Conditioners We RecommendOver the last couple of months, we've been vetting and testing portable and window air conditioner units.