Does your smartphone use more energy than a refrigerator? A recent report by the Digital Power Group claimed that an average iPhone uses more juice for battery charging, data use, and wireless connectivity than a medium-sized, ENERGY STAR refrigerator.

But an iPhone's power requirements vary dramatically depending on how it's used for video, gaming, and other apps. And estimates for just how much data the average owner uses a month also vary widely, so the controversial study has <a href=">drawn critics who claim that the comparison is greatly overstated. (See quiz: "What You Don't Know About Electricity.")

Whether your mobile phone's power use rivals your fridge or not, the chances are good that hidden energy hogs in your home are burning more power and money than that refrigerator—sometimes much more. Here are half a dozen surprisingly power-hungry devices that may be feeding your electric bill.

Set-Top Boxes

These familiar electronic arrays sit on or near many televisions to connect cable to our entertainment systems. But it's not just their clocks that run when no one is watching. These devices function much like mini-computers that communicate with remote content sources or record favorite shows while you're out. That means they require a lot of energy.

"The issue with set-top boxes is that they never power down and they are almost always consuming their full power requirements even when you think you've turned it off," said Noah Horowitz, a senior scientist at Natural Resources Defense Council (NRDC). "If you have a DVR on your main TV, and a regular set-top box on a second TV, that could equal the energy use of a new refrigerator."

In 2010, an NRDC study found, the 160 million set-top boxes in the U.S. consumed the annual output of nine average coal-fired plants, some 27 billion kilowatt hours in all. That equals the total household electricity consumption of the entire state of Maryland. That kind of power costs money—more than $3 billion a year in electric bills—and most of that cash is spent on boxes running at full power while nobody is watching or recording their content. "We're spending about $2 billion a year in electricity bills to power set-top boxes when they are not even in use," Horowitz said. (See related story: "Who's Watching? Privacy Concerns Persist as Smart Meters Roll Out.")

Marianne DiMascio, with the American Council for an Energy-Efficient Economy's Appliance Standards Awareness Project (ASAP), said while more efficiency gains are needed, the industry has set some voluntary efficiency standards and made some recent improvements. "Today you can ask your provider for an ENERGY STAR-rated set-top box, and that will help," she said.

Furnace Fans

"There's a major energy eater lurking in your basement," ASAP's Marianne DiMascio said. "Many people don't even realize that they have a furnace fan, or have any idea how much energy it consumes."

Furnace fans circulate air from your furnace or heat pump, through the duct system, and into every room in your home. In homes with central air conditioning, they circulate cool air through the same system. "It's on a lot, and it's a very high energy user," DiMascio said of the double-duty device.

In fact, though they are hidden away in the basement, these fans are among many households' biggest energy users, responsible for almost 10 percent of the average American household's total electricity use, or 1,000 kWh each year—double or triple refrigerator usage—according to ASAP stats. That total is split roughly evenly between heating and cooling costs.

Energy efficient motors, like brushless permanent magnet (BPM) models, can cut this daunting number by 60 percent. These motors aren't mandated by federal standards, at least not yet, but they are available on many condensing furnaces and an increasing number of traditional models as well.

Battery Chargers

Many of the devices we use every day, from mobile phones to power tools, run on rechargeable battery power. The U.S. Department of Energy estimates that some 800 million such devices are sold in the U.S. each year, and the ultimate source of their power is the electric grid.

Many charging systems use outdated technologies that waste electricity. The state of California has tackled this problem by establishing tougher in-state efficiency standards. Currently the U.S. Department of Energy is working on its own regulations to make the devices more energy-efficient. If California's standards were adopted nationwide, the savings could be enormous, DiMascio said. "If we improve standards for these battery chargers and external power supplies we could save American consumers about $1 billion annually," she said.

While other products offer homeowners a chance to realize their own savings by product choice, she argues, these devices are an example of where regulation plays the key role. "Nobody right now is going to go out and buy a computer or a cell phone according to how efficient the battery charger is. So in this case the standards are overcoming a market barrier of people not really being able to go out and buy efficient chargers for all of these devices."

(Energy-wise or an energy waster? Test yourself with our Personal Energy Meter.)

Microwave Ovens

You'd expect your microwave to eat up electricity when it's popping popcorn or heating up last night's leftovers. But the truth is, these appliances consume most of their electricity when they're simply sitting in your kitchen doing nothing. "You only use a microwave a tiny part of the time," DiMascio said. "But when it's not in use, it's consuming standby power because it's always sitting there ready to go."

An Appliance Standards Awareness Project study found that the typical microwave is only used about 70 hours a year. During the other 99 percent of the time, or 8,690 hours, it burns as much as 35 kilowatt hours in "vampire power" to illuminate the clock and keep electronic push button controls in standby mode.

"There are ways to make that standby power lower," DiMascio added, and new U.S. Department of Energy regulations announced in June may help do just that. The new standards coming into effect in 2016 will cut that wasteful consumption by 75 percent for most microwaves by upgrading efficiencies in power supplies, control boards, and cooking sensors.

Sara Mullen-Trento of the Electric Power Research Institute said smaller, cheaper electronics mean that more appliances will likely boast electronic features like those on microwaves. "You'll probably see this kind of technology incorporated to enhance their feature sets," she said. "Things like a digital display on a clothes washer. But I think with those consumer electronics playing a bigger role in consumption, we'll also see the newer efficiency standards recognize that this has an impact when you have ten of these devices in the home. In fact, some of those same feature sets may allow you to operate an appliance in a more energy-efficient way by using different settings."

Game Consoles

Powerful game consoles like the Xbox360 and PlayStation 3 have important power-saving features, but also some significant issues, said Noah Horowitz.

"They feature an on/off button, which puts the console into a standby mode with less than one watt of power usage, which is what it should be—they work great," he said. Unfortunately many users don't turn the units off, or turn off the television but leave the console powered up—a costly mistake.

"If you run the console 24/7 because you don't turn it off, it could cost you an extra hundred dollars a year," he said. Newer consoles now ship with an auto power-down feature that launches the standby mode after periods of inactivity. Older units have the feature too, Horowitz explained, but require users to visit the menu and make sure the device's power-saving mode is turned on.

Game consoles also hog power when they are used to stream movies, something makers like Sony and Microsoft are increasingly encouraging their users to do. "Streaming movies on a console like PlayStation 3 uses twice as much energy than if you stream the same movie with Netflix over a set-top box and about 30 times more energy than if you streamed the movie on Apple TV." The problem, Horowitz said, is one of power-scaling, and it's a challenge for console manufacturers.

"You'd like the console to turn off unused features. You don't need that powerful game processor when you're just streaming a movie, but right now the consoles are not designed to differentiate between those tasks."

(How much can you save by switching lighting at home? Try the Light Bulb Savings Calculator.)

Pool Pumps

Americans love to stay cool in their swimming pools and dig more than 150,000 in-ground units each year, adding to a total that's already more than 5 million. While some bemoan the heating costs for some pools, another, larger expense often goes unnoticed: the pool pump accounts for 70 percent of a typical pool's energy use and seven times that of a refrigerator.

The pump keeps pool water circulating and passes it through filters. Single-speed pumps always run at the same maximum speed, burning extra energy. But multi-speed pumps can be scaled up or down as needed for tasks like filtration and cleaning.

Using an ENERGY STAR-certified pump with multiple or variable speeds can cut energy use by over 80 percent and save hundreds of dollars a year. According to ENERGY STAR stats, these pumps will pay for themselves in five years and save owners more than $1,000 over the pump's lifetime. Some utilities are offering cash incentives to purchase them and, in California, sales of new standard single-speed pumps have been banned outright.

"An average refrigerator uses around 500 kilowatt hours a year, while the average pool pump uses 3,500 kilowatt hours a year," Marianne DiMascio said. "So we're looking to get these more efficient pumps into pools."

(See an interactive view of how countries around the world generate their power.)