Clothes washers are defined by type: front-loading or top-loading; and by capacity: standard or compact.
In December 2007, Congress enacted EISA, setting the first minimum water efficiency requirements for clothes washers. Minimum energy efficiency requirements, however, were left unchanged from the existing levels set by DOE in 2001, which became effective in January 2007. The 2007 standards which went into effect on January 1, 2011, required residential clothes washers to be manufactured with a modified energy factor (MEF) of at least 1.26 and a maximum water factor (WF) of 9.5 or less. MEF is expressed in cubic feet of washer capacity per kWh per cycle and incorporates the machine electrical energy consumption, the hot water energy consumption, and the energy required to remove the remaining moisture in the clothes. WF is expressed in gallons per cubic feet of capacity. A higher MEF indicates better energy efficiency while a lower WF indicates better water efficiency.
In May 2012, DOE adopted new clothes washer standards based on a 2010 agreement between manufacturers and efficiency proponents. DOE uses new metrics called IMEF (integrated modified energy factor) and IWF (integrated water factor) which add standby and off-mode energy consumption into the formula. The IMEF/IWF standard levels in the 2012 final rule are equivalent to the the MEF/WF levels in the negotiated agreement. Top-loading washers have a two-phase standard with a minimum 1.29 IMEF (correlates to 1.72 MEF) and maximum 8.4 IWF (correlates to 8.0 WF) effective March 2015 and 1.57 IMEF (2.0 MEF) and 6.5 IWF (6.0 WF) effective January 2018. Energy and water savings relative to current standards are about 33% and 19% respectively for the 2018 standard. Front-loading washers standards effective in March 2015 are 1.84 IMEF (2.2 MEF) and 4.7 IWF (4.5 WF) with 15% energy savings and 35% water savings relative to the current standards. According to DOE, the standards will save about 2 quads of energy, 3 trillion gallons of water and about 113 million metric tons of CO2 emissions over 30 years. DOE estimates total net dollar savings for U.S. consumers over that same period will exceed $31 billion. Currently, ENERGY STAR-qualified products must meet a minimum MEF of 2.0 and a maximum WF of 6.0.
Front-loaders are generally more efficient than top-loaders, although manufacturers have introduced some new high-efficiency top-loading models that are as efficient as some front-loaders. Until recently, top-loaders were much more common than front-loaders, but front-loaders now make up about half of annual sales. Clothes washer efficiency improvements can be achieved through advances in mechanical technology (efficient motors); reductions in the amount of water consumed to clean a given volume of laundry; and higher spin speeds to remove more moisture from the clothes at the end of the cycle.
Federal Documentation (DOE Web site)