Double pane windows provide insulation with an inert gas that the manufacturer seals into the space between the panes. It is usually argon or krypton, both of which are better insulators that air. 

    All insulated windows lose their gas over time as air gradually leaks into the gap between the panes, which brings along moisture. Manufacturers insert a desiccant, such as silica, between the panes to absorb any moisture intrusion, but it eventually becomes saturated and allows condensation to form on the interior surfaces of the glass. Dust in the air collects on the condensation and builds up over time, which gradually clouds the window. This is a normal process for a double or triple pane window as it reaches the end of its lifespan. The cloudiness is a cosmetic issue, but the loss of inert gas reduces the insulating ability of the window and affects the energy efficiency of the home.

    A back-and-forth action that has been dubbed “thermal pumping” contributes to the loss of the gas over time. It is the expansion and contraction, along with flexing in and out, of the glass and surrounding frame and seals with changes in temperature. Sides of a home exposed to direct sun are more prone to the effects of thermal pumping and it can’t be avoided. A window with southern exposure is most likely to have gas loss due to thermal pumping.

    But pressure washing double pane windows creates even more pressure and flexing of 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 visit a home less than 10-years old that the homeowner has pressure-washed and 90% of the windows are clouded over. 

    So don’t do it. Avoid expensive window replacements by washing your windows the old-fashioned way with a soapy solution and garden-hose water pressure. Although pressure washing is one cause of premature clouding of double pane windows, a manufacturing defect or poor installation that squeezes the frame can also cause seal failure. Further investigation may be necessary if you have a large number of windows in your home cloud over at the same time, but no history of pressure washing.

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  To learn more about doors and windows, see these other blog posts:

• What causes sweating (condensation) on the inside of windows in the winter? 

• Is every exterior door of a house required to have a landing outside? 

• What are the small slots at the bottom of the outside of my window? 

• Why does condensation form on the outside of some windows and not others in the morning? 

• Why is the garage door track a white tube? 

• What is the raised metal plate on the floor under the garage door?

• How many exit doors are required for a house?

• How many exit doors are required for a mobile/manufactured home? 

• Are openable windows required to have window screens? Will windows with no screens pass a home inspection? 

• Does a home inspector test all the windows and doors in a home? 

• How difficult is it to change a window to french doors or a sliding glass door?

• How do you determine if a door is left-handed or right-handed?

• Why are window security bars dangerous? 

• What are the common problems you find inspecting windows?

• What is causing a foggy haze on my windows? 

• What do those numbers on the manufacturer's stickers in new windows mean?

• What does a home inspector check on an electric garage door? 

• What is the tempered label on glass at windows and sliding glass doors called?

• Do I need to have two exterior exit doors in my house? 

• When is safety glass required for windows at stairs and stair landings?

   Visit our DOORS AND WINDOWS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.