Windows, Part 6

more than 144 pounds over just a single day! A standard four by four foot window has sixteen square feet of glass and twenty thousand pounds of pressure on those panes of glass. This window might “breathe.

As more and more moist air enters the space between the panes the drying agent finally fills with moisture and can no longer hold any more. At this point the moisture settles on the interior surface of the window and make the window “fog,” or look like a shower door after you have taken a shower.

Cardinal Glass and others have tried to solve this problem by adding a thin vent tube. The vent tube is maybe even a foot long and is hidden inside the edge of the window frame. As the panes of glass balloon in and out from temperature and pressure changes, a little air can move up and down inside that tube. The tube is long enough that no outside air actually gets into the window.

Beware.

Installing dual pane windows can be tricky and the edge seal of the window can break even upon installation of the window in the home and yet the window won’t fog for many years because the drying agent keeps the window looking good ’till the warranty period has been passed!

Yes, shoddy installation can destroy the window seal and you won’t discover it until the warranty expires. There is usually more than enough absorbant in the window edge to keep the problem a secret.

There are other reasons for the window seal to fail. The home can shift on its foundation or there can be an earthquake or there can be other factors which twist or bend the window (even a deep loud noise can shake the window) and the seal between the panes can be broken. Once that seal is broken the window will eventually fog. When the window fogs the homeowner, today, faces about a $1,600 replacement cost for each window (if they go back to the same supplier).

What all of the information above has told you is that dual pane windows are a fact of life, that they are delicate, that they do work -- for a while -- and that they even can save you money on your energy bill.

Of course, there is no way that you can possibly ever save enough money on your energy bill to replace a $1,600 window every five or ten years... Unless that is, you live on some very cold and windy spot in Antarctica.

How can this be? Well, lets take the average home in a place with four seasons. Two of