Are Your Windows Leaking Cold Air?

The cold air below your window
probably isn't leaking from outside!

Homeowners often falsely believe that their windows are leaking when they feel cold air moving near the bottom, or below, the sill of the window. Now, on the one hand, it could well be that some of the draft that  one feels when placing a hand at the bottom of the window really is from a leak, but under no circumstance would that be the only source of moving air. Consider that the glass of a window gets fairly cold, even on the inside of the house, when the weather is cold outside. Now, since air is up against the window, the air cools as well. Now ask yourself: what happens when air cools? Right--it sinks! Then, warmer air moves in to replace it, only to be cooled in turn, and to then sink toward the bottom of the window. Even then, as the air is sinking, it remains in contact with the window and cools further as it drops.

This cycle of cooling and sinking air creates a spot on the base of your windows which is cold and feels drafty, given that the air is moving toward the floor. The bottom line is: your windows probably aren't leaking, or at least, not as much as you imagine from feeling the airflow. So relax. I've seen people threatening to sue over supposed "leaks" which were in fact just air circulation--and they make first-rate idiots of themselves in the process. Don't be one of those people. Of course, if you can see a gap, that's a different story.