Wednesday, January 25, 2012

Drafty Window...or Convective Looping?

Most everyone at one point or another has experienced cool air that shoots from the windows and into the rest of the room. The “Drafty Window” is one of the most common complaints we hear from homeowners looking for more comfort in their castle.  Conventional wisdom has always stated that the cold air coming through the window is the cause of the drafty window; a window that has its structure compromised—somehow—and lets in that cool air in during winter months.  The concept of the drafty window is a staple of our energy (in)efficiency language.       

The truth?  Most of the time, it isn’t the window leaking air—it’s convective looping.

As the graphic illustrates, warm air (which likes to sit at the top of our rooms) reaches the window and comes in contact with the cold glass.  What happens to cold air?  It sinks.  In fact, that air turns colder and colder, picking up speed as it slides down the window to the floor.  It hits the floor and, since it can’t go through the floor, it zooms to the center of the room where it eventually is displaced by the next cycle of colder air and then…rises to the top of the room.  So the cycle repeats.  Over and over and over…  

And another thing: in the event that cold air is actually coming from outside the home, it probably isn’t coming around the glass, the sash or the window itself: it is likely sneaking around the window trim or the casing around a window frame.  All too often, window and door trim (or baseboard, for that matter) isn’t caulked or sealed.  Frequently it is easier for that cold air to go around the window framing than through the window.  Look at the connection between the window trim and the wall.  Is there a crack or gap?  If so, that is the likely spot where cold air is getting into your house and stealing your money.

Now, if you do have a problem with a loose sash that is letting air through the body of the window itself, then there is a temporary fix for that that doesn't require you to seal the trouble spot permanently: Seal 'N Peel temporary caulk can be applied in winter and removed in Spring when you want to open your windows.  It's the best of both worlds.  (Though, it is scented like vanilla because it stinks pretty good.  Prepare for 24 hours of this.)      

To fix the leaky window trim problem: caulk will stop the infiltrating air.

To fix the convective loop problem: well, it can’t be stopped completely.  Heavy drapes can help, but won’t completely stop the air current.  Air can still be drawn in from the sides or top of drapes.  Weatherizing windows with plastic sheeting is the best way to mitigate the cold window surface that draws the air from the top of the room to the floor.

And if you are having difficulty identifying which problem you have, call us.  We can help.