Air can leak in and out of a home through cracks around doors and windows, joints between different materials, pipe and wire penetrations, and other gaps and openings. Recessed ceiling lights, electrical outlets and switch plates, plumbing penetrations and any joints between unlike materials are all potential sources of air leakage. This leakage can increase heating and cooling costs and reduce indoor comfort.

As part of your regular maintenance schedule, be sure to check your home for signs of air leakage. You can check for leakage yourself by simply holding your hand in front of potential leaks on a cold day and feeling for drafts. The most effective way to detect air leakage sites is to have a qualified contractor perform a "blower door" test, which can often identify leaks in places you wouldn’t think to look. Many contractors now offer this service, often combined with a full range of corrective measures. Sealing air leakage through the use of caulking, weatherstripping or other measures can save a substantial amount on your heating and cooling bills without requiring outside help. Reducing air leakage can also improve comfort by eliminating cold winter drafts.

As a general rule, you should caulk any cracks or openings between surfaces which do not move relative to each other and where a permanent seal is desired.

Most types of caulk can be applied on either the inside or outside of the home. Caulk interior cracks, joints, and other openings to help prevent conditioned air from leaking out of your home. In the winter the heated indoor air contains water vapor which can condense if allowed to reach a cold surface. Inside surfaces should be made as airtight as possible to prevent conditioned air and water vapor from escaping toward the outside. If the air is allowed to leak into wall cavities, the resulting moisture can damage insulation and other materials

Caulk exterior openings or penetrations to prevent moisture from entering the structure and to help "weatherproof" your home. Protect the outside of the building against rain and weather, but allow any moisture to escape that may migrate from the interior into wall cavities.

Caulking materials come in a variety of types, some for general applications and others for more specialized uses. Elastomeric caulks, including silicone, latex and acrylics, will remain flexible over time and are preferred over the older oil-based caulks. Be sure to check labels carefully to ensure that the type of caulk you select is suitable to your intended application. Today's improved caulking materials are designed to last for 20 years or longer, and to retain their flexibility to provide a tight seal under a wide range of conditions.

• Step 1

  Clean the surface of paint build-up, dirt, and deteriorated caulk with a screwdriver, putty knife, or wire brush. All surfaces should be clean and dry before application.

• Step 2

  Cut the tip of the caulk nozzle at a 45 degree angle. It is best to cut the hole a little smaller than you think you will need; you can always enlarge it later. Hold the caulking gun and cartridge at a 45 degree angle, squeeze the trigger slowly, and push or pull the gun and cartridge evenly along the joint. The bead of caulk should be just wide enough to adhere to both sides of the crack or joint. Apply the caulk in a continuous neat bead.

  Fill any cracks larger than 1/4 inch with fiberglass scraps or other suitable materials before sealing with caulk.

• Step 3

  Use a putty knife or the tip of your finger to tool the caulk into the crack and smooth the exterior surface.

Caulking materials which come in rope form can be pressed into cracks and later removed if desired. This is sometimes used as a form of temporary weatherstripping on old, loose windows.

Aerosol foam sealants can be used for sealing larger cracks and openings around pipe and wire penetrations, and at the foundation sill joint. These foams expand to fill the opening and provide a good, tight seal. Be sure to follow the manufacturer's instructions when using this type of product.

For electrical outlets and switches, pre-cut foam rubber gaskets can be purchased and installed directly behind the cover plates to eliminate air leakage through the outlet box.

Weatherstripping should be used in joints or between surfaces which must be free to move such as:

• where doors meet their frames (including doors to unconditioned spaces like garages)
• where windows meet their frames (depending on the type of window, these can include top and bottom sashes, center rails, and side channels)
• around attic access or drop-down stairs.

The weatherstripping product you purchase should have a minimum effective life of at least five years. Vinyl V-strip and spring metal weatherstripping both work well on most windows and doors. Adhesive backed weatherstripping should be stapled or tacked in place to ensure a useful life. Doors that have a gap at the bottom (between the door and the threshold) can be fitted with a "door sweep".