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Air Sealing

Air infiltration may contribute to as much as 30% of your building's heating and cooling costs. Infiltration wastes energy and money, and contributes to moisture, noise and dust problems. These openings may also serve as an entry way for unwanted pests.

Finding Leaks

Areas that may have significant leaks are near the attic, crawlspace, or basement, and around windows, doors, and chimneys. Plumbing chases, electrical outlets, attic accesses, and dropped ceilings are other likely suspects. Leaky ducts are also a big source of loss. Your heating system may be working hard to heat and distribute air that never reaches its intended destination.

An energy professional will use a blower door and other diagnostic tools to identify air leaks. You will be able to detect large cracks and gaps in the walls by the resulting drafts. You can hold an incense stick near suspect areas and watch the smoke for telltale drafts. However, you may need to hire a contractor to run tests to determine the location of smaller air leaks. An energy professional will use diagnostic tools such as a blower door to locate air leaks and pressure imbalances.

Fixing Leaks

Holes in the envelope of the house should be repaired from largest to smallest.

Air sealing should be performed before insulation is added as gaps and cracks in the wall will allow air passage, decreasing the effectiveness of the insulation.

Air sealing should be performed in conjunction with an assessment of the building's ventilation system to ensure adequate indoor air quality. This is especially important when combustion appliances, such as gas-fired water heaters, are present. Without proper ventilation these appliances can backdraft and draw exhaust gases, including carbon monoxide, into the living space. This can pose a potential health hazard.


There are several materials that may be used for air sealing, depending on the purpose.

Backer rod - Closed-cell foam or rope caulk. Press into crack or gap with screwdriver or putty knife. Often used with caulk around window and door rough openings.

Caulk- For sealing gaps of less than ½ inch.

Spray Foam- To fill large cracks and small holes. A few precautions should be heeded when using spray foam: do not use near flammable applications and do not use expanding foams around windows and doors.

Weatherstripping - To seal areas with moveable components such as doors and windows.

For larger areas:

Housewrap - To form an airtight seal over the exterior sheathing, housewrap must be sealed with tape or caulk. Does not provide a vapor barrier.

Polyethylene Plastic - To serve as a vapor and air barrier. This material may be used for sealing complicated leakage areas that may be of irregular shape.

 Insulation Basics
 Duct Sealing and Insulation
 Caulking and Weatherstripping
 Do it Yourself Maintenance Schedule
 ENERGY STAR Home Sealing
 DOE Energy Savers - Air Sealing
 Building Envelope Links

Content updated May 28, 2009

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