Windows fail for a variety of reasons:
1. Flaws to the window during manufactuing. This includes voids and seperation of seals and the spacer bar.
2. Damage caused during transporation and installation.
3. Exposure and building pressure.
4. Day to Day atmospheric pressure.
Radiant Heat caused by atmospheric pressure is by far the most destructive.
During the day as the sun rises, the air
molecules between the panes of glass
are heated. As the space is heated, this
causes the window glass to expand
apart.
As the sun sets in the evening and temperatures drop,
the molecules between the two panes of glass cool.
This causes contraction of the air space resulting in
the panes of glass contracting in towards each other.
This process of heating and cooling of the airspace is
called Solar Pumping. As the air between the glass cools,
it cannot hold as much water vapor as warm air.
The result is water droplets in your window.
This is the same process that creates dew on the grass.
If Solar Pumping is a natural process, why don't all windows show moisture?
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