The efficiency of a dishwasher is measured by a term called the energy factor. The energy factor is somewhat similar to the miles per gallon for a car, but in this case the measure is cycles per kilowatt-hour of electricity. The minimum allowed energy factor rating for standard capacity dishwashers is 0.46. About 80% of the total energy used by a dishwasher goes towards heating the water. So the best way to improve the efficiency of a dishwasher is to reduce the amount of water needed to clean the dishes.
New dishwashers use about half the electricity of 25-year-old models. Most new dishwashers have a built-in booster heater, which raises the water temperature of the water during wash cycles to 140°F to kill germs and cut grease. While this feature adds somewhat to the dishwasher's electric demand, it enables you to lower the thermostat setting on your hot water heater to 120°F. Each 10°F reduction in the water heater temperature setting will save up to 13% of your hot water heating bill and also reduce the danger of scalding.
Most manufacturers offer high-efficiency dishwasher models. These dishwashers use less water and more significantly, less energy than the standard models. A typical high-efficiency dishwasher can wash a load of dishes using 5 to 7 gallons of water and use substantially less energy. Estimated annual energy use for high-efficiency dishwashers ranges from 214 to 558 Kilowatt-hours (kWh) per year with an average of 504 kWh.
Federal law requires that EnergyGuide labels be placed on all new dishwashers. These labels are bright yellow with black lettering. Look for the EPA’s ENERGY STAR label when purchasing a new dishwasher. This label indicates the machine is energy efficient. For information on the Energy Star program, specific high efficiency dishwashers, and where to purchase these machines visit the Energy Star web site.
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