clock menu more-arrow no yes mobile

Slash Your Utility Bill with a DIY Energy Audit

This Old House tells you how to find and fix 12 potential trouble spots to boost your home's efficiency and save you money

Use Less, Spend Less

Photo by Laura Moss

So you've swapped your incandescent lightbulbs for CFLs, turned down the thermostat, and only wash clothes on cold. Then why are your utility bills still so high? Air leaks are likely culprits, but so are "phantom" power suckers, such as flat-screen TVs, which draw energy even when they're off.

To help pinpoint exactly where you are burning through resources—and cash—we polled energy consultants across the country. The simplest route, they agree, is to have a professional auditor detect leaks with sophisticated tools, such as blower doors and infrared cameras. Your local utility may offer this service for free, but if it doesn't, the cost is typically $400. Or you can do some easy tests yourself and put your money toward addressing the problems. "There are many steps homeowners can take before calling a pro," says Jeffrey Gordon, spokesperson for the New York State Energy Research Development Authority. "With a little knowledge and determination, you might be surprised by your next power bill." Read on to learn how to spot and stop some of the biggest energy wasters.

Drafty Windows

Photo by Laura Moss

The problem: Outside air comes in and warmed air escapes through leaky frames, accounting for 10 to 25 percent of your heating costs.

How to spot it: On a blustery day, close all windows and exterior doors and the chimney-flue damper. Light a stick of incense, move it around the perimeter of each window, and watch for air that interrupts the delicate rise of smoke.

How to stop it: First check the window from the outside, paying close attention to where its casing meets your home's siding. "This is an area that often doesn't get the kind of attention it needs," says Ted Kidd, an energy consultant in Rochester, New York. Scrape out any cracked or dried caulk, and apply a fresh bead of paintable acrylic latex, such as DAP's Alex Plus. On the inside, add new weatherstripping. For a few hours' work, you can make an old wood double-hung airtight using a kit like the Easy-Stop Weather-Stripping System ($74 per window; The kit contains a silicone flap for the bottom rail of the lower sash and a pile strip for its top meeting rail. Also included are new paintable cellular PVC parting beads (narrow bands that separate the upper and lower sashes) with built-in insulation.

The payoff: Shave up to $20 off your annual energy bill for each window you weatherize.

Mystifying Utility Bill

Photo by Laura Moss

The problem: Most bills don't break down energy consumption by category, such as heating, cooking, and lighting, making it almost impossible to target where you are overspending.

How to spot it: Sign up for one of the dozens of new pilot programs offered by regional utility companies to help homeowners pinpoint and control their usage with a digital energy-management system.

How to stop it: Hook major appliances and electronics up to smart plugs, or relays, which transfer information to a Wi-Fi–enabled control panel that sits at a central location in your home, such as the kitchen counter. This device—it can also switch appliances on or off and adjust a programmable thermostat from home or remotely via a computer or smartphone—gives you a real-time look at how much energy you're using in kilowatt hours and dollars. "You can determine immediately what's costing you the most money and decide if it's worth keeping that item plugged in," says Paige Layne of Duke Energy, which is currently supplying customers with Cisco's Home Energy Controller (shown at left) free of charge in select markets in the South and Midwest. If your utility isn't offering such trials, you can buy a monitoring kit at an electronics store, such as Best Buy, for as little as $100.

The payoff: Save 10 to 25 percent on your electric bill by tracking down unwanted energy hogs and using the consumption data to change your habits.

Damaged Fireplace Damper

The problem: Ten to 20 percent of warmed air from your home can be drawn into the chimney flue, passing around a rusted, stuck, or loose-fitting damper.

How to spot it: With the damper closed, hold a lit candle inside the firebox and watch the flame. If it gets beaten around or blown out, air is flowing up the chimney.

How to stop it: Hire a chimney sweep. In addition to giving the chimney a good cleaning, lubricating and checking the damper is usually part of the $90 to $200 service call. In the off-season, when the fireplace isn't in use, you can seal the flue completely with a balloonlike plug, such as the Fireplace Draftstopper ($55;, that you inflate and insert up the chimney just in front of the damper. When cold weather starts again, simply deflate the plug for easy removal.

The payoff: Reduce your annual heating bill by up to $500.

"Phantom" Appliances and Electronics

Photo by Laura Moss

The problem: Devices with a so-called standby mode that sap power even when they aren't in use can account for 10 percent of your electricity costs.

How to spot it: If it has an indicator light, a charger or AC power adapter on the cord, or a digital clock, it's a phantom. When in doubt, plug the device into a Kill A Watt detector (shown below, $22;, which measures exactly how much power is being drawn from the outlet when the device is supposedly "off."

How to stop it: Put phone chargers, the flat-screen TV, and computer and stereo equipment on power strips. "That way you can easily flip a switch and cut power directly from the outlet before going to bed," says energy consultant John Meeks of AppleBlossom Energy in Concord, North Carolina. Plug devices that are best left on 24/7 directly into dedicated surge protectors, he says; your DVR, for instance, needs power to record programs when you aren't around to watch them. And if you get phone service through the Internet, you'll want to keep your router juiced, too.

The payoff: Save $55 a year just by cutting standby power to your DVD-VCR player, stereo tuner and CD player, and video-game console.

Tip: To cut your dishwasher's energy usage in half, pull out the racks after the final rinse cycle and let your dishes air-dry.

An Old Tank-Style Water Heater

Photo by Ryan Benyi

The problem: Heaters that are more than 10 years old tend to be lined with fiberglass insulation, which is less effective at preventing heat loss than the foam used today.

How to spot it: Check the heater's date of manufacture printed on a sticker or metal plate on the side of the tank. Next, touch the tank. If you feel warmth, it's lacking insulation.

How to stop it: Wrap the tank in a precut blanket with an insulating value of at least R-8. Some utilities offer rebates on the $10 to $20 jackets and will even install one for free. To further boost efficiency, fit foam sleeves or insulating tape around pipes. "If your hot-water lines are exposed, that's a lot of energy lost as water travels through them," says Logan Brown of Efficiency Vermont, a nonprofit energy advisory agency. Covering cold lines keeps condensation from beading up on the pipes, helping to prevent mold and mildew in your basement, says Brown.

The payoff: An insulating blanket alone can reduce annual water heating costs by up to 9 percent.

Under-the-Door Air Infiltration

Photo by Kindra Clineff

The problem: While most homeowners weatherstrip around the jamb, they often overlook the area beneath an exterior door.

How to spot it: Close the door on a piece of paper placed on the threshold and give it a tug. If it pulls out easily, air is passing through.

How to stop it: Install a sweep seal. This metal strip with a piece of vinyl attached uses spring action to close the space between the threshold and door. There are also foam, vinyl, and felt seals that fit under the door or on the threshold to prevent air transfer. Whichever type you choose, it's an easy DIY installation that'll cost just $10 to $20.

The payoff: Coupled with weatherstripping, a sweep seal can prevent 11 percent of the outside air that typically seeps in around exterior doors from getting into interior spaces.

Leaky Ductwork

Photo by Courtesy of

The problem: After years of service, the adhesive on tape that seals joints between duct sections can dry out, allowing heated or cooled air to escape. Damage can also occur when homeowners or tradespeople access or work in areas where ducts are installed, such as crawl spaces, attics, and basements.

How to spot it: With the furnace or AC on, shine a high-powered flashlight on ducts, especially at junctions where they connect with registers. "If you see where dust on the exterior of the ducts has been blown away, that's usually the sign of a leak," says Meeks.

How to stop it: Patch small holes or misalignments with a water-based mastic sealant and mesh tape. Use HVAC foil tape to seal joints between sections.

The payoff: Cut your heating bill by 3 to 10 percent by reducing air leakage by up to 15 percent.

Overworked Fridge

Photo by Laura Moss

The problem: Your fridge never gets a day off. Over time, wear and tear on the door's rubber gasket, as well as built-up dirt and dust on coils, erode its efficiency and make it more expensive to operate.

How to spot it: Close the refrigerator door on a piece of paper. If you don't feel resistance when you pull it out, the gasket seal is broken and chilled air is escaping. Mold or moisture on the gasket are other telltale signs, says Brown.

How to stop it: Order a new gasket from the fridge manufacturer for $60 to $90, depending on the make and model. Remove the damaged gasket and install the replacement yourself, following the manufacturer's instructions. While you're at it, use a long-handled duster to clean the exposed coils located underneath or on the back of the appliance. For a fridge more than 20 years old, no amount of maintenance will bring it up to today's efficiency standards. It's better to retire it and invest in a new, Energy Star–qualified model. KitchenAid's new Architect Series II French door fridge even goes a step further—it has an efficiency rating that's 20 percent higher than the U.S. Department of Energy standard.

The payoff: Replacing the gasket and cleaning the coils can improve your fridge's cooling abilities by 25 percent. Swapping a 1980s fridge for a new, Energy Star one can shave more than $100 per year off your electric bill and nearly $200 annually if you have a 1970s model.

Exterior Wall Openings

Photo by Courtesy of Black and Decker

The problem: Holes for sewer and water lines, exhaust vents, and cable and phone lines are typically rough cut and uninsulated, so warmed or cooled air from inside your house escapes and outside air seeps in.

How to spot it: Use a handheld infrared thermal leak detector, such as Black & Decker's TLD100 ($49.99; Pass the device over the solid wall near the hole, then the hole itself. If you see a significant difference in temperature, you've got an air leak.

How to stop it: Fill minor gaps of less than ¼ inch with silicone caulk. For larger voids up to 1 inch wide, use expanding polyurethane foam insulation. The long applicator straw on cans of spray-foam sealants, such as Great Stuff, are particularly handy for accessing hard-to-reach areas inside sink vanities and behind heavy washers and dryers. "If you're dealing with a gap near a combustible device, like a fireplace, make sure you're using products approved for high temperatures," says Brown.

The payoff: Prevent 17 percent of treated air from escaping your home by sealing gaps around exterior penetrations.

An Attic Hatch that's not Airtight

Photo by Karim Shamsi-Basha

The problem: Little more than a thin sheet of plywood (so that it can easily be pushed up and out of the way), an uninsulated hatch can suck as much treated air out of living quarters as a fireplace chimney.

How to spot it: With all windows and doors closed, turn on the air conditioner or furnace and do the incense-stick test around the hatch; watch for smoke seeping between the access panel and the wood trim frame it rests on.

How to stop it: Secure rigid foam insulation to the back side of the hatch with duct tape, and affix foam tape around the edges of the panel to create a gasketlike seal. For pull-down stairs, add an insulated fabric housing, such as the Attic Tent (starting at $200; Secured to the attic-side framing with staples, the tent has a zippered hatch for easy attic access.

The payoff: An airtight hatch leading to a well-insulated attic can save you 30 percent on your heating bill.

Uninsulated Switches and Outlets

Photo by Laura Moss

The problem: A thin metal or plastic plate isn't enough to prevent air from getting through what's basically a big hole in the wall.

How to spot it: Remove the plate and cover the opening with a ply of tissue affixed to the wall at the top with painter's tape, like a curtain. If the tissue billows, you've got a leak.

How to stop it: Insulate the opening with a precut foam gasket, about 10 cents each at home centers. Just fit the gasket over the opening and replace the cover. For extra protection for outlets when they aren't in use, insert plastic child-safety plugs.

The payoff: Two percent off heating and cooling costs.

Outmoded Furnace

Photo by Keller & Keller

The problem: While gas-fired furnaces can last 20 years or more, ones made before 1992 are only 55 to 78 percent efficient, compared with up to 97 percent for today's.

How to spot it: If your furnace has a pilot light, it's likely more than 20 years old and only about 60 percent efficient. If this telltale sign isn't present, ask an HVAC pro to inspect the furnace and assign it an annual fuel utilization efficiency (AFUE) rating based on its age. An AFUE of 80, for instance, means that 80 percent of the fuel burned is converted into heat for your home.

How to stop it: Replace an old furnace with a properly sized modern unit with a high AFUE. Manufacturers now display the rating right on the furnace so that consumers can easily compare the efficiency of various models. Expect to pay $2,500 to $4,000, including installation. On the high end are ultraefficient furnaces with a rating of 97, such as Trane's XV95. Its variable-speed fan motor adjusts to provide a consistent flow of warm air, making your home more cozy and saving you extra cash over the long haul.

The payoff: Cut your heating-fuel bill by more than 30 percent by replacing a 60-percent-efficient furnace with one that's 97 percent efficient.