It often surprises people to learn that with today’s water-conserving dishwashers and typical practices for hand-washing, properly filled automated dishwashers use less water and energy. If you wash dishes by hand and leave the water running when washing or rinsing, hand-washing almost certainly uses more water. Even if you try to be miserly and use plastic tubs for wash water and rinse water, you may well be using more than the most efficient of today’s dishwashers, a few of which use less than four gallons for a full wash and rinse cycle.

About 60% of the energy used by dishwashers is to heat the water—both by the water heater in your house and through an integrated booster heater in the dishwasher. That booster heater takes the incoming hot water, say at 120 degrees F, and boosts the temperature to about 140 degrees. Dishwasher detergents need such hot water to work most effectively, and the high temperature also aids drying of dishes. Most of the other energy used in dishwashers is to operate pumps and dry dishes at the end of the final rinse cycle.

If you’re buying a new dishwasher, look for an Energy Star model. For a standard-size dishwasher, federal law, as of January 2007, requires that it have an Energy Factor greater than 0.46. (The Energy Factor for dishwashers accounts for mechanical energy use, the energy for water heating, and the energy for drying; it measures the number of cycles a dishwasher can run using 1 kilowatt-hour (kWh) of electricity.) To carry an Energy Star logo, a dishwasher has be have an Energy Factor of at least 0.65—41% higher than the federal minimum. Both the federal standard and Energy Star standards are scheduled to be further tightened over the next two years.

Here are other recommendations when buying and installing a new dishwasher:

• Look for the soil sensing feature. “Soil sensor” technology, available on more advanced dishwashers, automatically adjusts the water consumption according to how soiled the dishes are. Less water and energy are used for a load of relatively clean dishes.

• Make sure the dishwasher has energy-saving wash cycles. The ability to select different wash cycles depending on how dirty the dishes are may save water and energy. It is common to have “light wash,” “normal,” and either “pots and pans” or “heavy wash” cycles.

• Make sure there is a no-heat drying option. This allows you to avoid use of the energy-guzzling electric heating element at the end of the last rinse cycle for drying dishes.

• If possible, avoid installing the dishwasher next to the refrigerator, as waste heat from the dishwasher will make your refrigerator compressor work harder.

• Whether you have a new or older dishwasher, here are some tips for using it more efficiently:

  • Scrape dishes before loading them. Modern dishwashers do a great job, and don’t require pre-rinsing. If you insist on pre-rinsing, at least use cold water, and turn on the water only as needed.
  • Don’t always wash dishes after a single use. In our household, we each have our own water glass and use it multiple times before washing, and I’ll sometimes reuse a plate that only had a sandwich on it.
  • Fill the dishwasher completely. Avoid washing partial loads; wait until the dishwasher is filled before running it, even if that takes several days. You might need to buy some extra silverware or dishes if you find you operate the dishwasher only partially full because you’ve run out of clean dishes or utensils.
  • Fill the dishwasher according to the manufacturer’s recommendations. The water spray should be able to reach all of the dishes, so you can’t pack them too tightly—but you don’t want to leave empty space either.
  • Use energy-saving wash and dry cycles. Whenever possible use the “light wash” cycle, and you should almost always be able to use the energy-saving “no heat dry” setting. At home, we almost always use the “no heat dry” setting. Partially opening the dishwasher door after the rinse cycle will speed up air-drying.
  • Turn down your central water heater temperature—probably. If you currently have your water heater set to “high”—about 140 degrees F—it usually makes sense to turn it down to about 120 degrees. With your water heater set at a lower temperature, the dishwasher will boost the temperature to about 140 degrees. If you heat your water very inexpensively, however, such as with a wood boiler during the winter, keeping the temperature setting higher so that the dishwasher’s electric booster heater isn’t needed may make sense, since electricity is more expensive than wood heat.

  For more on dishwashers, the Consumer Guide to Home Energy Savings, published by the American Council for an Energy Efficient Economy (ACEEE), is a handy resource. The 9th edition of this book should be available at the library, through a local book store, or at www.aceee.org.