More than 60 percent of American kitchens have a dishwasher, and 93 percent of newly built homes include them. According to the Consortium for Energy Efficiency, dishwashers account for 2.5 percent of the energy used in a typical household.

Energy Guide label Dishwashers are one of the types of appliances for which the federal government sets efficiency standards. This EnergyGuide label found on all new dishwashers estimates the amount of energy in kilowatt-hours (kWh) that this model consumes, provides an estimate of its yearly operating cost, and compares it with the energy use of similar models. Since the label is created by the U.S. Department of Energy and not the appliance's manufacturer, it provides shopping consumers with a valuable comparison tool.

Efficiency standards have made dishwashers much more efficient. Today's dishwashers use less than half as much energy and water as those made before 1994. Since almost 60 percent of the energy a dishwasher uses goes toward heating water, models that use less water also use less energy.

Energy and water savings can be even more impressive in dishwashers displaying the ENERGY STAR label. These efficient models feature energy efficient motors and such advanced technology as:

  • Soil sensors that assess how dirty dishes are throughout the wash and adjust the cycle to clean with a minimum amount of water and energy;
  • Improved water filtration to remove food particles to insure dishes come out sparkling;
  • More efficient jets and innovative dish rack designs to maximize cleaning.

A pre-1994 dishwasher uses an extra $40 worth of energy a year and wastes more than 10 gallons of water per cycle compared to a new ENERGY STAR model. Since a dishwasher has an average lifespan of 11 years, an ENERGY STAR qualified dishwasher will save an average of 1,300 gallons of water over its lifetime, compared to an old machine.

Types of dishwashers

Mechanical dishwashers all work in a similar way - they spray soapy hot water over and across dishes to clean them. The water must be at least 140 degrees to melt dishwasher soap and clean greasy dishes. All dishwashers manufactured in the US today include a booster heater that increases and maintains the temperature of your home's hot water.

There are several types of dishwashers:

  • The traditional, built-in, under-the-counter dishwasher
    This style is permanently plumbed into your home's water and plumbing system. Standard width is 24 inches. ENERGY STAR estimates a "standard" dishwasher has "a capacity greater than or equal to eight place settings and six serving pieces."
  • Compact built-in, under-the-counter dishwashers
    ENERGY STAR defines a compact dishwasher as one "being able to fit less than eight place settings and six serving pieces." These are usually 18 inches wide, designed for tight spaces and small kitchens.
  • Portable dishwashers
    Portable dishwashers come in both standard and compact sizes, are mounted on wheels, have finished sides, usually feature butcher-block tops and come with water hookups to attach to your sink faucet. They drain into your sink. They offer an option when cabinet space in your kitchen is at a premium and a standard dishwasher cannot be installed. Portables can be rolled into a closet or across the room when not in use. They offer an easy option for renters who want a dishwasher but can't remodel a kitchen that doesn't have one.
  • Countertop portables
    A variation on the roll-around dishwasher, these models, roughly the size of a microwave oven, sit on a counter. Most units are no more than 17 inches tall and fit between the counter and any overhead cabinets. They provide a good choice for apartments, office kitchens or tiny kitchens. When in use, they are temporarily connected to the faucet and they drain into the sink. Some models claim to hold as many as six normal-sized place settings.

Smart Buying

Consider these energy tips when shopping for a new dishwasher:

  • Check the EnergyGuide label to compare the energy usage of different models. ENERGY STAR qualified dishwashers are the most energy saving.
  • Consider the size of your family. A compact dryer might be better suited to the needs of just one or two people. Compact models use less energy, but they also hold fewer dishes. Having to run a compact dishwasher several times to clean your family's dishes will result in greater energy use.
  • Know how much space you have to install the dishwasher. If your kitchen is tight, you might choose to go with a portable model.
  • Look for features like "energy-saving" and "short-wash" cycles. Using more efficient operating cycles helps you use less water and save energy.
  • Choose a dishwasher that gives you heat-drying and air-drying options. Heat-drying elements use considerable energy; air-drying options use very little.
  • Consider a model that allows you to set the time for the dishwasher to run. This way you can wash dishes later in the day, when electricity rates may be cheaper.

Smart Use

Once you've purchased an efficient dishwasher, consider these tips to cut the amount of energy and money you spend operating it:

  • Try to wash only full loads - the savings will surprise you.
  • Use short cycles for everything but the dirtiest dishes. Short cycles use less energy and work just as well.
  • Most new dishwashers clean well enough that you don't need to pre-rinse your dishes. If you do rinse dishes before loading them, use cold water. Don't waste water by letting the faucet run continuously.
  • Avoid using the "rinse hold" setting on your dishwasher. This feature uses 3 to 7 more gallons of hot water for each use. Never use "rinse hold" for just a few dirty dishes. Instead consider the old-fashioned hand wash/rinse basin option.
  • If your dishwasher has an air-dry setting, choose it instead of the heat-dry setting. You will cut your dishwasher's energy use from 15 percent to 50 percent. If there's no air-dry setting, turn the dishwasher off after its final rinse and open the door. The dishes will dry without using any extra electricity.
  • Because new dishwashers automatically heat water to 140 degrees, you can lower the thermostat setting on your hot water heater to 120 degrees F. Each 10-degree reduction in water heater temperature setting can save up to 13 percent on your hot water heating bill. Setting the water heater to 120 degrees F. also reduces the danger of scalding.
  • If you have a choice, install your dishwasher away from your refrigerator. The dishwasher's heat and moisture increase your refrigerator's energy consumption. If you have to put them next to each other, place a sheet of foam insulation between them.

Dishwashing vs. handwashing - which is greener?

Which is better for the environment, washing dishes by machine or by hand? Which technique uses less water?

It's a frequently asked but complicated question. The prevailing opinion is that machine-washing is greener by far, but the answer depends on variables like these:

  • How efficient - or how big - is your dishwasher?
  • Do you use it as efficiently as possible, running full loads and using the light cycle when possible?
  • If you're washing dishes by hand, do you let the water run?
  • Do you fill up the sink to wash and rinse?

One often-quoted study at the University of Bonn in Germany found that washing dishes by machine used only half the energy, one-sixth of the water, and less soap than washing by hand.

Cost savings will vary depending on the price of your water and energy, but the ENERGY STAR program estimates using one of their qualified machines instead of hand washing will save on average 5,000 gallons of water and $40 in utility costs each year, along with 230 hours of your time.

Remember, too - by saving water, you're also saving the energy used to pump it, treat it, and clean it up afterwards in your city's waste water facility. Up to 50 percent of a typical city's energy bill goes to supplying water and cleaning it after use! Saving water pays in many ways.