Even tiny air leaks around windows and doors can lead to significant increases in the cost of heating or cooling a home. As the winter months approach, it is especially important to replace old weather stripping and identify any points of vulnerability. Once you know where they are, you can immediately resolve the problem.
The easiest way to check for window and door air leaks is to use your sense of touch. This won't work for tiny cracks, but it should reveal any major gaps between windows and doors and their frames. Simply hold your hand one or two inches from the frame and move it slowly around each door and window. If you feel a draft or a change in air temperature, it could signal the presence of an air leak.
This works best when the temperature outside is considerably different from the temperature inside. The best time to use this method is during the heat of the summer. It is also most effective to wet your hand prior to conducting the test. If the temperatures are not significantly varied, other methods will work better.
Another way to check for window and door air leaks is employ a flashlight at night. Remove as many other light sources as possible (e.g. table lamps, floor lamps, outdoor flood lights), then turn on a high-powered flash. One person holds the flash inside while another follows his progress outside.
When the flashlight is aimed at the edges of each door and window, the outside partner looks for any light leaks. Move slowly around the frame and communicate about light angle and any other considerations.
Sometimes light and ambient air aren't reliable indicators of air leaks in doors and windows. A third option is to close a piece of notebook or copy paper in a door or window. Tug on the paper, and if it slides out without ripping, there is likely too much of a gap.
Perhaps the most reliable way to test for window and door air leaks is the pressurization test. It isn't foolproof because you aren't using expensive equipment. However, it will reveal smaller cracks and gaps that the other methods will not.
Turn off all heating or air conditioning units in the house. Close windows, doors, and fireplace flues, then run all the exhaust vents in the house. Stovetop and bathroom fans work well for this purpose.
This method requires two people unless there is significant wind. One person goes outside with a portable fan, while the other remains inside with a candle, incense stick, or disposable lighter. The inside partner sparks a flame and moves it around each door and window while the outside person directs air with the fan. If the smoke changes direction or the flame is extinguished inside, there is probably a leak.