structural:expansion
United States

Top-loading and front-loading clothes washers are covered by a single national standard regulating energy consumption. The old federal standards applicable before January 2011 did not restrict water consumption; there was no limit on how much unheated rinse water could be used. Energy consumption for clothes washers is quantified using the energy factor.

After new mandatory federal standards were introduced, many US washers were manufactured to be more energy- and water-efficient than required by the federal standard, or even than required by the more-stringent Energy Star standard. Manufacturers were further motivated to exceed mandatory standards by a program of direct-to-manufacturer tax credits.

In North America, the Energy Star program compares and lists energy-efficient clothes washers. Certified Energy Star units can be compared by their Modified Energy Factor (MEF) and Water Factor (WF) coefficients.

The MEF figure of merit states how many cubic feet (about 28.3 liters) of clothes are washed per kWh (kilowatt hour). The coefficient is influenced by factors including the configuration of the washer (top-loading, front-loading), its spin speed, and the temperatures and the amount of water used in the rinse and wash cycles.

Energy Star residential clothes washers must have an MEF of at least 2.0 (the higher the better); the best machines may reach 3.5. Energy Star washers must also have a WF of less than 6.0 (the lower the better).