Uniform energy factor
UEF
Uniform energy factor (UEF) is the federal efficiency rating for residential water heaters: the higher the number, the less energy the water heater uses for the same hot water.
DOE’s Federal Energy Management Program describes UEF as a metric used to compare the energy conversion efficiency of residential appliances and equipment. Electric resistance and gas water heaters rate below 1; heat pump water heaters rate above 1 because they move heat from the air instead of making it.
Reference points: a standard electric tank at 0.95, ENERGY STAR gas storage models at 0.81 or 0.86 depending on size, ENERGY STAR gas tankless at 0.95, and ENERGY STAR integrated heat pump water heaters at 3.30 or more. For the same fuel, energy use scales with 1 ÷ UEF.
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