From the US Department of Energy, published on December 31, 2008 and retrieved on Wednesday, January 7, 2009:
The U.S. Department of Energy (DOE) today announced the availability of ENERGY STAR® residential water heaters. With today’s announcement, the ENERGY STAR® program now addresses every major residential appliance found in most American homes. Introduction of this product provides significant potential savings to consumers. Water heating represents up to 15.5 percent of national residential energy consumption, the second largest end use of energy in homes, following heating and cooling. Using one of five specified water heating technologies, ENERGY STAR® qualified water heaters can reduce water heating bills from 7.5 percent to as much as 55 percent.
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Click here for a link to the Energy Star website.