Air Leak Testing & Sealing

Seal air leaks and save money

Check your dryer vent

If cold air comes in through your dryer vent, check outside where the vent goes through the wall. The vent should have a flap (or flaps) at the end to stop air infiltration. Make sure there’s a flap and that it’s not stuck open. If the flap works well, check the caulking. If it’s cracking and peeling away, it’s probably allowing cold air to leak in. Cut away the old caulking, make sure the vent is flush against the siding, and apply new latex caulk.

If the flap doesn’t close on its own, try cleaning it and then spray silicone on the pivot point. If the flap still won’t close, replace it. A new vent costs about $5 at home centers, and installing it will only take about 15 minutes. Start by cutting away the caulking around the vent with a utility knife, remove any screws and unclamp the duct leading to the dryer. Slide the old vent out of the wall, slip in the new one and reattach it to the duct. Caulk around the vent flange.

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Fill gaps around electrical boxes

The gaps around electrical boxes in exterior walls and ceilings are breezeways for cold air. If the gap between the electrical box and the drywall is less than 1/4 in., fill it with latex caulk. If the gap is bigger and lopsided, use foam sealant that's formulated for use around doors and window framing. The minimally expanding foam won't drip down your walls.

Turn off the power to the electrical box and use a noncontact voltage tester to ensure there’s no power. Remove the cover plate. Spray the foam around the box to seal it. After it dries, cut away any protruding foam, add a foam gasket (to reduce drafts through the box) and replace the cover plate. Do the same around register openings on the inside of exterior walls.

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Seal leaky windows (Option 1)

Leaky windows are one of the biggest sources of energy loss in a typical home. If you don’t want to cover your entire window, a quick, low-cost solution is to seal the gaps with removable caulk. A $4.50 tube seals five 3 x 5-ft. windows.

Apply the caulk over the cracks between the movable parts of the window (sashes) and the stationary parts (jamb) and between the two sashes. Keep the bead between 3/16 and 1/2 in. wide. Don’t run your finger over the bead after caulking (the caulk will be harder to remove later). In the spring, simply pull off the caulk. Clean off any residue with mineral spirits.

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Seal leaky windows (Option 2)

If you don’t like the look of caulk on your windows all winter long, cover them with plastic film instead. A $13 kit covers five 3 x 5-ft. windows. The plastic also reduces window condensation and can be used with curtains or blinds. The film is available for the exterior and interior.

Apply double-sided tape (included) to the window casing. Cut the film roughly to size with scissors, leaving a few extra inches on each side. Starting at a top corner, apply the film firmly to the tape around all four sides of the window. Use a hair dryer to remove the wrinkles. When winter is over, take down the plastic and pull the tape off the casing. The tape removes easily without damaging the finish.

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Stop under-the-door-leaks

If you can feel the breeze and see daylight under your entry door, it’s costing you big-time. It also means you need to adjust your door threshold or install a new door sweep. Door sweeps start at $10. Usually, the hardest part about replacing the sweeps is taking off the door. Start by adjusting the threshold. Newer versions have screws that raise and lower the threshold. Turn all of the screws until the door opens and closes without much drag and any draft is eliminated. If that doesn’t work, or your threshold doesn’t have adjustment screws, replace the door sweep.

Close the door and pop out the hinge pins with a pin punch to remove the door. Set the door on a work surface and remove the old door sweep. Caulk the ends of the door, then install the replacement sweep. Some sweeps are tapped into place and stapled along the door bottom; others are screwed to the side along the door bottom.

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Caulk and cover room air conditioners

A room air conditioner keeps a section of the house cool. The problem is, it’ll keep the room cool all winter long if it isn’t covered properly. If you have a window unit, the best solution is to remove it so the cold air won’t flow through and around it. If you decide to leave it in or you have a permanently installed wall unit, grab some removable caulk and a $4 window air conditioner cover to keep out the cold.

Place the cover over the outside of the air conditioner, fitting the sewn-in corner straps over the bottom corners. Wrap the middle straps under and up the sides of the unit, then hook them over the top. Inside the house, apply removable caulk around the air conditioner where it meets the wall or window. If the air conditioner is a built-in unit, permanently seal it with latex caulk.

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Fill gaps under sinks

Pull back the escutcheons on plumbing pipes where they enter exterior walls and you'll probably see generous gaps around the pipes. In cold weather, you might also feel the draft coming in. All it takes is some $7-a-can expanding foam to seal those leaks. Shake the can vigorously, then squirt the foam around the pipes inside the wall. Don't completely fill the gap—the foam will expand. If it expands too much and you can’t get the escutcheon back on, wait for it to dry, then slice it flush with the wall with a utility knife.

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Find air leaks

Locating air leaks can be tricky. They're often so small as to be hardly noticeable. To find them, follow a trail of smoke. Close all the windows in the house, turn off all the fans and exhaust fans, and shut off the furnace. Light some incense and walk slowly around the outer walls of the house. Anywhere you notice the smoke blowing away from something or being sucked toward something, there's probably an air leak. Now that you've found it, seal it!

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Seal small attic holes with foam and caulk

Hot air rises, so leaks in the ceiling are even worse than leaks in walls. And in many homes, this airflow through ceilings and into the attic is the No. 1 source of heat loss. You can check for leaks around ceiling light fixtures and the attic access door using an incense stick. But the only way to detect other leaks is to crawl up into the attic, pull back the insulation and look for them. Most leaks occur where chimneys and electrical and plumbing lines pass through the ceiling. Although the attic is a nasty place to work, plugging these leaks is a simple project—mostly caulking and foaming gaps.

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Stop a draft in 60 seconds

In exterior walls, electrical boxes that hold switches or outlets can let in a lot of cold air. Worse, they can let warm, moist indoor air into walls, causing problems like wood rot or peeling exterior paint. One way to stop the airflow is to seal the gaps around them and the holes inside them with caulk—messy and time-consuming. But there's a much easier way: With foam gaskets, all you have to do is unscrew the cover plate, stick the gasket in place and put the plate back on. A pack of a dozen gaskets costs about $3 at home centers and hardware stores.

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