How efficient are mini AC units?

As of 2015, the Department of Energy certifies 22 models of air conditioners with outputs less than 6,000 Btus as energy-efficient appliances through its Energy Star program. These units must have a minimum energy efficiency ratio of 10.0 or better to qualify for Energy Star certification.

Most mini air conditioner units have an output of approximately 5,000 Btus, sufficient for cooling rooms of 150 square feet in area or less, though no industry-wide definition of which units qualify as mini air conditioners exists. Energy-efficient mini air conditioners are estimated to use 15 percent less energy than air conditioners that do not have Energy Star certification.