Appliances and other items that qualify for the federal government's Energy Star program use less energy than other products in their category. An Energy Star-qualified refrigerator, for example, uses at least 20 percent less energy than the maximum amount allowed under the current federal standards.

But in an interesting twist, Energy Star qualification could lead some people to buy a product that uses more energy than one that doesn't. How's that?

A look at snack foods can help explain this conundrum. In recent years, health experts have warned consumers against ignoring the serving sizes of low-fat snack foods, as noted in a study from Cornell University. It turns out that some folks tend to wolf down more of a food labeled low-fat and end up eating as many as or more calories than they otherwise would have. A similar thing happens when people buy a more power-hungry product just because it carries the Energy Star sticker.

"Energy Star, in some cases, can be somewhat misleading for consumers and can even lead to a perverse incentive for people to purchase larger and more energy-consumptive products," says Jennifer Thorne Amann, director of the buildings program for the American Council for an Energy-Efficient Economy, a Washington, D.C.-based nonprofit that promotes energy efficiency. "By buying on Energy Star alone, some people are actually costing themselves a lot—not only by buying a more expensive product but also by spending much more to operate it."

Consider the 48-inch GE Profile PSB48LSRBV built-in side-by-side and the 327/8-inch GE GTS22ISSRSS top-freezer. The $6,950 side-by-side uses 645 kWh annually and is Energy Star qualified while the $1,179 top-freezer uses about 18 percent less energy but does not qualify for Energy Star because it uses more energy than the most efficient top-freezers with similar capacity.

We're not suggesting that these are apples-to-apples comparisons—consumers who prefer the above side-by-side should buy it, knowing that it is among the most efficient built-in side-by-sides on the market. But you don't want to shop based on Energy Star qualification alone since it does not guarantee absolute energy savings.

You'll also need to use the information on the Federal Trade Commission's EnergyGuide label (shown) for the products you're considering and compare their annual energy use. (Before you shop, refer to your monthly utility bill to see how much you pay for electricity and/or gas. That cost will help you determine the annual operating cost of an appliance or other product.) 

And don't forget to do your research on ConsumerReports.org before you head to the store. Not only will you get valuable buying advice, including ratings and brand repair history, but for many products you'll also find our efficiency ratings, which we believe better reflect how you use the products you buy and how much they'll cost you each year. Armed with this information, you'll make wiser choices all around.—Ed Perratore