Dishwashers are one of the greatest kitchen conveniences, just ask anyone who has lived without one for any length of time. For a major appliance, the dishwasher doesn’t use much energy on its own. Where the energy impact occurs is in heating the water the dishwasher uses. Heating the water represents more than 80% of the dishwasher’s total energy use. Since this is the case, most of the measures you apply to improving your hot water efficiency will benefit dishwashing energy efficiency as well (see the section on water heating).
Dishwashers generally use between 8 and 14 gallons of water for a wash cycle. The range can be varied depending on which setting you select, from light rinse to pot-scrubber mode.
Some people keep their home's water heater temperature set at 140°F because their dishwasher requires this temperature to break down powdered dish soaps. However, most dishwashers have built-in heaters to boost water temperature up to 140°F to 145°F, the temperature range recommended by manufacturers for best dish washing performance. Having a booster heater allows you to turn your water heater thermostat down, which will reduce water heating costs.
Use your dishwasher's lightest wash setting that will do the job as the less water used, the lower the cost of operation. An easy way to save money on the dishwasher is to use the “no-heat dry” option. If your dishwasher does not offer this setting, wait for the final rinse cycle to finish then open the door and let the dishes dry rather than allowing the electric heating element to come on. And try to only run the dishwasher when it has a full load.
When looking for a new dishwasher, look for the Energy Guide label that tells how much electricity, in kilowatt-hours (kWh), the dishwasher will use in one year. Also look for the EnergyStar logo indicating the dishwasher exceeds federal standards by at least 13%.