How to Find Leaks in a Window Frame

Leaking window frames are a source of heat loss.

Leaking window frames are a source of heat loss.

Loose fitting window frames are a common source of drafts during cold, windy weather. In addition to causing discomfort, they can increase the cost of heating and cooling your house. The source of a small window leak may not be obvious on casual inspection. Knowing what to look for and how to look simplifies finding these potentially expensive leaks.

Initial Inspection


Inspect the window frame for leaks visually by looking for light coming through any part of the window other than the glass. Gaps around the outside of the frame or between the sliding portion of the window and frame large enough to admit light provide an easy path for air transfer in and out of the house.


Gently shake the sliding portion of the window. The gaps that allow a window section to rattle or is shake loosely inside the track are often the source of a leak.


Shake the exterior window frame. If the frame moves easily inside the framed opening, it is probably leaking air and should be secured in position and caulked.

Negative Pressure


Close all exterior doors and windows as well as any other open fireplace or furnace flues.


Turn off any forced air heating or cooling systems. The breeze coming out of the heating/cooling vents may make detecting drafts difficult.


Create negative pressure inside the house by turning on any bathroom and kitchen exhaust fans. Drawing air from the inside of the house makes a slight vacuum and forces outside air into the house through any available opening.


Light a stick of incense.


Hold the incense two to three inches from the window frame. Move it slowly around the outside and inside of the frame while watching the trail of smoke. A disturbance in the smoke trail indicates the presence of a leak.

Things You Will Need

  • Incense stick

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