My Double-Paned Window Fogs During Cold Weather

Construction

• Double-glazed windows are made from a single sash or casement that encloses two sealed panes of glass. Typically, air is removed by vacuum, often replaced by a gas such as argon. The lack of air and presence of gas conducts heat less efficiently than air, causing an insulation effect. The most efficient windows have UV and infrared barriers to boost their efficiency.

Failure

• The seal is prone to failure from house movement, breakage and temperature extremes. Water vapor infiltrates the void, which condenses on the outside pane in cold weather. In summer, vapor can condense on the cold interior window of an air conditioned house. Sometimes the condensation comes and goes seasonally, but it often stays put. Over time, visibility through the window diminishes, and the window becomes more and more unsightly.

Solution

• Once a window seal has failed and the glazing has fogged, there is no remedy except replacement. If your window manufacturer still makes your window, you may be able to replace a single sash or casement, as opposed to replacing the whole window, frame and all. The energy efficiency of a window with a broken seal is not necessarily compromised, so replacement is an aesthetic decision.

Prevention/Alternatives

• Avoid rough handling of windows by not letting sashes slam shut -- or open, if you have casements. Keep spring balances and casement hardware in good working condition. Guard windows against stray mop handles and baseballs. For whole-house window replacement, consider single-glazed windows and storm windows. This time-tested option allows maintenance between the panes and flexibility when glazing needs to be replaced.