I believe that insulated glass, in its present form, is a
fundamentally flawed idea. For those who don't know it, an insulated
window is made of two pieces of glass with an air space separating
them. This dead air space, filled with inert nitrogen gas, is supposed
to reduce outside noise and lower temperature loss through the widow.
It does do an excellent job of noise reduction, but it does a
negligible job of saving energy.
The dead air space is protected by a rubber, silicon or petroleum
based seal that keeps the totally dry, dead air in and the moist air
out; for a while. The basic problem with this concept is that these
windows get alternately hot and cold 365 times a year, especially if
the windows get a lot of sun exposure. That means the seals expand and
contract until the inevitable breach occurs. It may take 15 years, or
15 days, but it's coming. When it does, the air inside the window will
expand and escape out the breach in the seal.
When the window cools, the air inside contracts and sucks in the
highly humid air we have here in Florida. Thus begins the fogging
effect that we begin to notice as that air gets hot and the moisture
turns to steam in between the panes. It usually starts as just a small
amount, but it grows and grows until the window is actually dripping
wet inside when it cools. I have seen this happen for 20 years, even
to windows that have never been power washed.
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