Seal drafts; save money

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Warmed or air-conditioned air mixes with outside air through gaps in your homes thermal envelope -- exterior walls, windows, doors, the roof, and floors.

Such air leaks can waste large amounts of energy.

Most experts agree that caulking and weather stripping any gaps will pay for itself within one year in energy savings. Caulking and weather stripping will also alleviate drafts and help your home feel warmer when its cold outside.

However, these two weatherization techniques cant replace the need for proper insulation throughout your home.

Assessing air quality

Because caulk and weatherstripping limit indoor-outdoor air circulation, you should assess your indoor air quality before you apply them. Some homes contain dust, mold, carbon dioxide, and other indoor air contaminants.

Sealing air leaks in these homes, without proper ventilation, can also seal in their indoor air pollutants. Therefore, any plan to tighten the thermal envelope of a home should be accompanied by a look at your homes ventilation needs.

Detecting air leaks

You may already know where some air leakage occurs in your home, such as an under-the-door draft that makes you want to put on socks. But youll probably need to search to find the less obvious gaps.

Look at areas where different materials meet, like between brick and wood siding, between foundation and walls, and between the chimney and siding. Also inspect around the following for any cracks and gaps that could cause air leaks:

  • Door and window frames
  • Mail chutes
  • Electrical and gas service entrances
  • Cable TV and phone lines
  • Outdoor water faucets
  • Where dryer vents pass through walls
  • Bricks, siding, stucco, and foundation
  • Air conditioners
  • Vents and fans.

Depressurize your home to help detect leaks. On a cool, very windy day, turn off the furnace. Shut all windows and doors. Turn on all fans that blow air outside, such as bathroom fans or stove vents. Then light an incense stick and pass it around the edges of common leak sites. Wherever the smoke is sucked out of or blown into the room, theres a draft.

Or just turn on all your exhaust fans (dont need to turn off the furnace) and try one of these methods:

  • At night, shine a flashlight over all potential gaps while a partner observes the house from outside. Large cracks will show up as rays of light. Not a good way to detect small cracks.
  • Shut a door or window on a piece of paper. If you can pull it out without tearing, youre losing energy.

For a more thorough and accurate measurement of air leakage, you can hire a technician to conduct a blower door test in your home.

Blower doors are variable speed fans with a frame and shroud that allows them to fit inside a variety of door frames. Pressure gauges determine airflow through the fan, as well as fan-induced pressure.

The leakier a house, the more airflow required to induce a pressure difference. When used as a diagnostic tool, a blower door can also reveal the location of many leaks.

Caulking selection

You can use a caulking compound to seal leaks in a variety of places throughout your home, including around windows and door frames.

In addition to plugging air leaks, caulking can also prevent water damage inside and outside of the home when applied around faucets, ceiling fixtures, water pipes, drains, bathtubs and other plumbing fixtures.

Caulk forms a flexible seal for cracks, gaps, or joints less than one-quarter-inch wide. Most caulking compounds come in disposable cartridges that fit in half-barrel caulking guns (if possible, purchase one with an automatic release). Some pressurized cartridges do not require caulking guns.

When deciding how much caulking to purchase, consider that youll probably need a half-cartridge per window or door and four cartridges for the foundation sill.

Caulking compounds can also be found in aerosol cans, squeeze tubes, and ropes for small jobs or special applications. Water-based caulk can be cleaned with water, while solvent-based compounds require a solvent for cleanup. Caulking compounds also vary in strength, properties, and prices.


Although not a high-tech operation, caulking can be tricky.

Read and follow the instructions on the compound cartridge. And save yourself some trouble by remembering a few important tips:

  • Clean all areas to be caulked for good adhesion. Remove any old caulk and paint, using a putty knife or a large screwdriver. Make sure the area is dry so you wont seal in moisture.
  • Hold the gun at a consistent angle. Forty-five degrees is best for getting deep into the crack. You know youve got the right angle when the caulk is immediately forced into the crack as it comes out of the tube.
  • Caulk in one straight continuous stream, if possible. Avoid stops and starts.
  • Send caulk to the bottom of an opening to avoid bubbles.
  • Make sure the caulk sticks to both sides of a crack or seam.
  • Release the trigger before pulling the gun away to avoid applying too much caulking compound. A caulking gun with an automatic release makes this so much easier.
  • If caulk oozes out of a crack, use a putty knife to push it back in.
  • Dont skimp. If the caulk shrinks, reapply it to form a smooth bead that will seal the crack completely.

This document was produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national laboratory. The document was produced by the Information and Outreach Program at NREL for the DOE Office of Energy Efficiency and Renewable Energy.

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