Sometimes, we barely notice those who do the most for us. This is often true with dishwashers, those kitchen workhorses that clean up after dinner with little fuss. We might complain that they're noisy or feel vaguely guilty about the water and electricity they use, but mostly we're glad that the dishes are getting done.

Like all hard workers, though, the dishwasher deserves some attention. Especially if it's an older model, it might use a lot more energy than necessary-primarily in the process of heating water. Older machines are also thirsty creatures. According to Energy Star, dishwashers today have improved motors and pumps that allow them to use about 30 percent less water and electricity than those made in the early 1990s; they're also about 50 percent quieter.

All of which means that it can make sense to upgrade your dishwasher, particularly if it was made before 1994, the year that strict federal efficiency standards were put in place. And if you don't have a dishwasher at all? Consider getting one. Sweating over a sink full of dirty dishes isn't likely to earn you any eco-martyr points. In fact, a new, efficient dishwasher can use significantly less water than washing dishes by hand, and it gets them cleaner, too. You don't even need to rinse them first (though, as you probably know, you should watch what you wash out with your wastewater). So what more incentive do you need?

Here's what to look for when you shop:

Dishwashers are classified in two sizes: standard and compact. These sizes are defined not by the dimensions of the machines themselves-since differences in rack placement and design can mean that some slim dishwashers can hold more than some broad ones-but by overall capacity. A standard dishwasher will hold at least eight full place settings and six serving pieces. A compact model is anything that will hold less than this. You'll want to choose the size that suits your family and lifestyle, bearing in mind that it's always more efficient to run full loads. If you live alone or rarely cook at home, a compact model might be right for you.

Heat-drying versus air-drying: Most modern dishwashers have a heat-drying feature that uses electric heating elements to dry the dishes. This consumes a large amount of energy, and is only marginally convenient. Look for a machine with the option to turn this feature off, or to choose air-drying instead.

Soil sensor: This nifty option allows the dishwasher to gauge, during the course of the wash, how dirty the dishes are, and adjust water use and cycle length to account for that. This can conceivably save energy over a standard timed cycle, since the machine will run only as long as necessary.

Booster heater: Here's a feature that is generally touted as energy-saving, and it certainly can be. What it does is boost the temperature of the water that comes to the dishwasher from your water heater to 140 degrees or so, the optimal temperature for getting dishes clean. This means you could get by with a cooler setting on your water heater (since you won't need water that hot for other household uses), thereby saving energy. If you have an electric water heater, this can be a boon. However, as Alex Wilson, co-author of the American Council for an Energy Efficient Economy's Consumer Guide to Home Energy Savings, points out: "If you heat water with natural gas or heating oil, that's a lot less expensive than electricity. Since the booster uses electricity, the argument could be made to keep your water heater set at a higher temperature, so the booster doesn't need to work as hard." You'll have to evaluate your own hot-water heating costs to know for sure.

Wash-cycle choices: Many dishwashers come with several wash-cycle options, including "light wash" for dishes that aren't especially dirty and "heavy duty" for pots and pans. These features allow you to control the length of the cycle and the amount of water used, based on your needs for a particular load of dishes. Using the light cycle can deliver real water savings, as it will likely use about three gallons less than a normal run.

Energy Factor (EF) and kilowatt-hours per year (kWh/year) When shopping for a dishwasher, you're bound to encounter the acronym EF, which stands for Energy Factor. This is the performance metric that federal standards and Energy Star use to compare dishwashers. Expressed in cycles per kWh, it reflects the energy used by the machine itself, as well as the energy used by the water heater, for each dishwashing cycle. The higher the EF, the more efficient the machine. Other performance specifications, such as those set out by the Consortium for Energy Efficiency (CEE), use both the EF and the estimated kWh/year consumed-assuming 215 cycles per year-to compare and rate dishwasher efficiency. The lower the kWh/year number, the better.

Energy Star This program is sponsored jointly by the Environmental Protection Agency and the Department of Energy. For a dishwasher to earn the Energy Star seal, it must use at least 41 percent less energy than the federal minimum standard; that works out to an EF of .65 or higher for standard-size machines, and .88 or higher for compact models. When you see that familiar blue star, you know the model is among the better performers. But keep in mind that not all Energy Star-rated dishwashers are created equal, and some offer exceedingly high efficiency, well beyond the program's requirements.

EnergyGuide This yellow sticker-created by the Federal Trade Commission-is required to appear on all dishwashers and numerous other household appliances in retail stores. It tells you the amount of electricity, in kWh/year, that the dishwasher will consume, assuming normal use and 215 cycles per year, and compares that figure with the consumption of other models in the same size category (standard or compact). This sticker also gives an estimate of annual operating costs. This can be helpful but offers only a rough guide, since using certain features can change energy consumption considerably. The EnergyGuide label may or may not display the EF.

Just looking: where to find the current recommended models
Once you have a general sense of the style, size, and features you're looking for in a dishwasher, it's smart to do a little bit more homework before making a purchase. First, contact your local utility company, and find out if it offers a rebate for purchasing a dishwasher on its list. According to Howard Newman, communications director for the CEE, many utility companies do so as an incentive to get old water-guzzlers taken out of service. Some utilities have a list they have compiled; others use the CEE's list of top-performing dishwashers-many of which go beyond Energy Star specifications for efficiency. You can also check in with Energy Star and take a look at the product list. There, you'll see every Energy Star-approved model on the market, and can compare them by EF, and the percentage by which each exceeds the federal minimum standard. Armed with that information, you can decide what would be smartest for you.

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