How to Find Air Leaks in Your House (and Seal Them Cheaply)

To find air leaks in your house, walk around on a cold or windy day and feel for drafts with a damp hand, or hold a lit incense stick near windows, doors, outlets, and pipes and watch for smoke that moves sideways. The biggest leaks are often hidden in the attic and basement, so check there too. Most leaks can be sealed in an afternoon with caulk, weatherstripping, and foam.

The Department of Energy says air leaks can account for up to 30 percent of a home's heating and cooling energy use. Finding and sealing them makes rooms more comfortable and lowers your bills.

7 easy ways to find air leaks

1. The damp hand test

Wet your hand and slowly move it around window frames, door edges, outlets, and baseboards. Moving air feels cool on wet skin, so drafts are easy to notice. This works best on a cold or windy day.

2. The incense or candle test

Close all windows and doors, turn off the furnace and fans, and turn on bathroom and kitchen exhaust fans. This pulls air out of the house so outside air comes in through leaks. Then slowly move a lit incense stick around likely spots. If the smoke blows sideways or gets sucked in, you found a leak.

Safety: Keep flames away from curtains and anything that can burn, and never leave them unattended.

3. The dollar bill test

Close a door or window on a dollar bill. If you can pull it out without any drag, the seal is too loose and air is getting through.

4. The flashlight test

At night, have one person shine a bright flashlight around a door or window frame from inside while another person watches from outside. Light shining through a gap means air can get through too.

5. Look for clues

• Dirty spots on carpet edges or insulation, where air has been filtering through
• Spider webs that move in corners
• Light coming in under doors
• Rooms that feel much colder than the rest of the house

6. Use a thermal camera

A thermal camera or a phone add-on shows cold spots as dark colors. Some hardware stores and libraries lend them out.

7. Get a blower door test

For the most complete check, hire an energy auditor. They use a big fan in a doorway to pull air out of the house, which makes every leak easy to find. Some utility companies offer free or low-cost energy audits.

The most common air leak spots

Many people only check windows and doors. But the biggest leaks are often in the attic and basement, because warm air rises and escapes through the top of the house while cold air is pulled in at the bottom.

How to seal air leaks

Tips for sealing

• Clean and dry the surface before using caulk or tape.
• Use the right caulk. Silicone works well outside, and paintable acrylic latex is good inside.
• Turn off power before putting gaskets behind outlet covers.
• Do not seal around furnace flues or chimneys with regular foam. Use fire-rated materials made for high heat.
• Keep the house breathing. A very tight home still needs fresh air. Run bathroom and kitchen fans, and keep an eye on humidity.

Sealing leaks helps with more than energy bills

• Fewer bugs. The same gaps let in pests. Our guide on keeping stink bugs out explains how sealing helps.
• Less condensation. Cold drafts near windows can lead to wet glass. See why windows get condensation.
• Warmer rooms. If some rooms stay cold even after sealing, your heating system may need attention. Check our guide on a furnace that blows cold air.
• Less dust blowing in from the attic and outside.

When to call a pro

• You cannot find the source of a cold draft
• Your attic has little or no insulation
• You want to seal around chimneys or furnace flues
• You want a full energy audit with a blower door test

Signs your home has air leaks

You may have leaks worth sealing if you notice:

• Drafts near windows, doors, or outlets
• Rooms that are hard to heat or cool compared to the rest of the house
• High heating and cooling bills, even when you keep the thermostat steady
• A dusty house, since leaks pull in dust from the attic and outside
• Dust marks on carpet edges under baseboards
• Ice dams on the roof in winter, often from warm air leaking into the attic

Seal first, then insulate

ENERGY STAR says homeowners can save an average of 15 percent on heating and cooling costs by sealing air leaks and adding insulation in attics, floors over crawl spaces, and basements. The order matters.

1. Seal the big leaks first. Start in the attic, then the basement or crawl space. These spots have the largest hidden holes.
2. Then add insulation. Insulation slows heat, but air can still move through it if gaps are not sealed.
3. Check how much insulation you have. ENERGY STAR notes that homes in warmer areas often need about 13 to 14 inches of attic insulation, and colder areas about 16 to 18 inches.

Caulk or weatherstripping?

A simple rule from the U.S. Department of Energy:

• Caulk is for gaps between parts that do not move, like where a window frame meets the wall. It works for cracks up to about 3/8 inch wide.
• Weatherstripping is for parts that move, like doors and windows you open.

Both are cheap, and the DOE says these projects often pay for themselves in a year or less.

A quick yearly air leak routine

• Fall: Check weatherstripping on doors and windows before the cold season.
• Winter: Do the damp hand or incense test on a windy day.
• Spring: Look at outside caulk around windows, pipes, and siding.
• Summer: Check the attic hatch seal and any holes around new wires or cables.

Many utility companies also offer free or low-cost home energy checks. Call yours or check its website.

What does a home energy audit cost?

A professional energy audit finds leaks you cannot see, often with a blower door test and a thermal camera.

Before you pay, call your electric or gas company. Many offer free or cheap audits, and some give rebates for air sealing done by an approved contractor.

Renting? Draft fixes you can take with you

If you rent, you may not be allowed to caulk or change weatherstripping. These fixes are easy to remove when you move out:

• Removable caulk for window gaps
• Window insulation film that shrinks tight with a hair dryer
• Thermal curtains to block cold air at night
• Draft stoppers at the bottom of doors
• Rugs on cold floors

Tell your landlord about big drafts. Fixing them saves energy for the owner, too.

The bottom line

Finding air leaks is easy with a damp hand, an incense stick, or the dollar bill test. Check windows and doors, but do not skip the attic and basement, where the biggest leaks often hide. Most leaks can be sealed with caulk, foam, weatherstripping, and door sweeps for less than $100, and the savings on your heating and cooling bills start right away.