How do you keep double-pane insulated windows from from getting cloudy?
Friday, May 22, 2020
The haze that obscures the glass in double-pane windows is caused by loss of the insulating gas sealed between the panes. This allows air to seep in, and then the humidity in the air to condense on the interior surface of the panes. Dust particles in the incoming air adhere to the wet glass and build up in layers over several years time. All double-pane windows lose their insulating gas evenutally, but there are two things you can do to keep the seal intact longer:
•• Do not pressure wash the windows. Pressure washing flexes the outside pane, with corresponding movement at the seal. It is possible to break the seal sufficiently to lose all the inert gas quickly when blasting a window with high-pressure water. We sometimes inspect a home less than 10-years old that the homeowner has pressure-washed and 90% of the windows are clouded over.
•• Provide shade at windows with direct afternoon sun exposure. “Thermal pumping" is the repetitive flexing in and out of the glass, due to expansion and contraction, of the glass and surrounding frame and seals that is caused by big, abrupt changes in temperature. Sides of a home exposed to direct sun are more prone to the effects of thermal pumping, and windows with southern exposure are the most likely to have this problem. Shading those areas with an awning or foliage, for example, will reduce thermal pumping.
And premature failure of the window seals can be caused by a manufacuturing defect. This is the most likely scenario if most of the windows fail within a few years. Vinyl windows have a higher rate of expansion/contraction that other window frame materials, resulting in more stress on the seals, and may have a higher early failure rate. The vinyl window shown at the top of this page has a southern exposure, no shade, and had lost its gas and began to haze over at three years old.
Also, double-pane sliding glass doors can have this problem too.
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