Window Replacement or Not?

Condensation is the accumulation of liquid water on relatively cold surfaces.

Almost all air contains water vapor, the gas phase of water composed of tiny water droplets. The molecules in warm air are far apart from one another and allow the containment of a relatively large quantity of water vapor. As air cools, its molecules get closer together and squeeze the tiny vapor droplets closer together as well. A critical temperature, known as dew point, exists where these water droplets will be forced so close together that they merge into visible liquid in a process called condensation.

Household air is humidified from high levels of water vapor in human and animal exhalation, plant transpiration, and fixtures such as showers and dryers. This humidity can rise significantly higher than outside air because of the insulative design of a house. Cold indoor surfaces can cool the surrounding air enough to force vapor to condense. This often happens on single-pane windows because they lack the necessary thermal insulation available to better windows. Double-pane windows have a layer of gas (usually argon or air) trapped between two panes of glass and should be insulated enough to prevent the accumulation of condensation. If this type of window appears misty or foggy, it means that its seal has failed and the window needs to be replaced.