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Office of Energy Efficiency Links


Personal: Residential

Repairing or Improving
Existing Windows or Doors


Finding Air Leaks

One of the quickest and easiest ways to reduce heat loss through windows is to seal air leaks with caulking and weatherstripping. This low-cost, do-it-yourself project can lower your heating bills and make your home more comfortable.

Finding air leaks is simple. On a cold or windy day, take a thin piece of tissue or plastic and hold it near your window frames. If the tissue or plastic flutters, you've found an air leak. You can also detect a draft by using the smoke of a lit incense stick as an indicator.

The next step is to seal the leak with caulking or weatherstripping.

Exterior Caulking

Exterior caulking prevents rain from entering the wall from the outside. The outside of a window should be caulked only after interior sealing is complete. If the exterior is caulked first, it can trap warm, moist air in the wall. In time, this can damage the wall.

Do not use exterior caulking products indoors – they may give off harmful fumes.

Interior Caulking

Caulking is used at fixed joints, such as where the interior window trim meets the wall or where the sash and frame come together in a fixed window.

Make sure the product is:

  • intended for indoor use
  • can be painted
  • is of good quality

On some windows, air leakage can be reduced by applying a continuous bead of caulking around the window trim, at the mitred joints of the trim, and between the trim and the frame. If a window is particularly leaky around the trim area and if the trim can be easily removed and re-installed, consider removing the trim, adding insulation and sealing the gap before re-applying the trim. If the gap is small (6 mm [¼ in.] or less), it may be enough to insulate the gap and then to caulk. Larger gaps may require the use of either a backer rod with caulking or an insulating low-expansion foam applied from an aerosol dispenser.

If you have operable windows that you do not intend to open and that are not needed as emergency exits, consider sealing them shut for the winter by using easy-to-remove tape or peel-and-strip caulking.

Figure 48