Almost all my windows in my house have air vents over them. As soon as I noticed this I was stumped. What is the reason for placing air vents near windows?
Air vents are placed near windows to help prevent “drafty” rooms. Windows are the coldest part of a room, and as air near a window is cooled it drops and creates uncomfortable drafts near the floor of the room. Air vents help prevent this by warming up the air before it has an opportunity to circulate. Air vents can also help to warm any air leaking through a badly installed window, as well as “washing” windows to prevent condensation.
Preventing Drafts
The biggest reason air vents are placed near windows is to prevent drafts. Windows are the coldest part of any room, especially in older buildings. Even in new buildings, with double pane glass, the r-value (a measure of how insulative something is) of the window is around 3 to 3.7. In comparison, a typical 2×4 stud wall with batting insulation will have a r-value of about 12.03. It’s easy to test this, just put your hand on a window in your house during the winter and you’ll feel how cold it is. Naturally any air touching this window is cooling down fast. And if we remember our high school physics class, hot air rises and cold air falls. This cold air is going to fall from your window to the floor, and be pushed along the floor by the air that is coming right behind it. Very quickly a draft will be sucked straight along the floor. Having cold air pulling around our feet and ankles is very uncomfortable, as our bodies naturally want to have cool heads and warm feet. This effect reverses that, creating uncomfortable conditions for the inhabitants of a room.
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