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Doing The Dishwasher

Our dishwasher is about 10 years old and seems to get louder each year. I also have to pre-rinse the dishes or they don’t get clean. Are the new dishwashers quieter and more efficient?—Paula N.

The use of an old water-guzzling dishwasher can have a significant impact on your water and power bills. Energy is used to power your water heater for the wash water and to operate the pumps and controls. Water is consumed for the actual washing.

Some of the new dishwashers use less than 5 gallons of water for a standard wash cycle. They have built-in water heating coils, so you do not have to keep your water heater temperature set excessively high. Different types of motors, pumps, and insulation improve the overall efficiency.

The newest dishwashers are not only more energy efficient, but quieter. Some manufacturers’ engineers told me their best models are more than 55 percent quieter than their best ones made 10 years ago.

The cleaning process is also improved, with some models having five spraying levels to reach every dish. The placement and design of the spray heads provide room for larger loads. A cleaning standard to which many new dishwashers are tested requires 10 place settings covered with egg yolk, oatmeal, tomato sauce, etc., dried on for two hours, to be thoroughly cleaned without pre-rinsing.

“Intelligent” dishwashers sense how dirty the dishes are and automatically run the proper number of wash and rinse cycles at the proper temperature to clean them. If left up to the homeowners, dishwashers usually get set to a maximum cleaning setting, which is overkill that wastes water and energy.

Most intelligent dishwashers sense the turbidity (cloudiness) of the wash water of each cycle to determine when the dishes are clean and no more cycles are needed. Some designs shine a beam of light through the rinse water to determine the turbidity.

Another method uses a pressure switch in the water circulation system. When the water is still dirty, tiny food particles build up on the filter screen. This buildup increases the pressure drop across the filter, indicating particles are still in the water. An electronic “brain” starts a brief filter flush cycle to clean it, and then the dishwasher continues to run until the screen indicates no more particles.

The energy efficiency of dishwashers is primarily a function of the hot water use, how long the dishwasher runs, and the level of insulation. Some internal water heating elements warm the water to as high as 170 degrees for faster cleaning. Some of the sound insulation is also effective for keeping the water warmer.

The most energy-efficient dishwasher models use a two-pump design with a separate smaller wash pump and a drain pump. By using two small pumps, the depth of the water reservoir can be reduced so less water is needed. One-pump designs reverse the pump rotation to switch from washing to draining. These are less expensive to make, but the larger pump requires a larger reservoir.

Another efficient option for small families is mini-dishwashers (called dishdrawers) that mount one above another in any cabinet under the countertop. They look like deep drawers and use only 2.4 gallons of water per cycle. Use just one for small loads or two together for medium loads.

The newer dishwashers also have many convenient features. A delay-start feature will run the dishwasher while you sleep. A built-in water softener can reduce spots. High-temperature antibacterial cycles are good for families with children.

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