EER is the Energy Efficiency Ratio, which is determined by U.S. Government standards and tests. The higher the EER number, the more energy-efficient the unit. According to Federal laws, all air conditioners must have the EER listed on a bright yellow tag attached to every unit. All air conditioners feature an EER of 8.0 or higher. The EER of a unit is calculated by dividing the number of BTU’s the unit is rated for, by the number of watts the unit uses.