Check your windows for signs of wear. ‘Foggy’ windows are not great to look at and can be costing you in energy bills. If multiple-pane windows appear misty or foggy, it means that the seal protecting the window assembly has failed. Below is a great explanation presented by The International Association of Home Inspectors.
Double-pane windows have a layer of gas – usually argon or air – trapped between two panes of glass that acts as insulation to reduce heat loss through the window. Other types of gas used in this space have various effects on heat gain or loss through the window. Some windows also have a thin film installed between panes that separates the space between the panes into two spaces, further reducing heat loss and heat gain through the window.
In a double-paned window, silica pellets inside the aluminum perimeter strip absorb moisture from any incoming air that enters the space between the panes. If not for the silica desiccant, any moisture in the space between the panes would condense on the glass as the glass cools below the dew point temperature.
Silica gel has an immense surface area, approximately 7,200 square feet per gram, which allows it to absorb large amounts of water vapor. As the sealant protecting this space fails over time, increasing amounts of moisture-containing air will enter the space between the panes and the silica pellets will eventually become saturated and will no longer be able to prevent condensation from forming. A double-paned window that appears foggy or that has visible condensation has failed and needs to be repaired or replaced.
Windows on the sunny side of a home will experience larger temperature swings, resulting in greater amounts of thermal pumping, seal stress and failure rates.
Vinyl window frames have a higher coefficient of expansion resulting in greater long-term stress on the double-pane assembly, and a higher failure rate. Windows also experience batch failure, which describes production runs of windows, especially vinyl windows, that are defective, meaning that the pane assemblies have been manufactured with seals that have small defects that will cause the window to fail prematurely.
If it’s allowed to continue, window condensation will inevitably lead to irreversible physical window damage. This damage can appear in the following two ways:
Riverbedding – Condensed vapor between the glass panes will form droplets that run down the length of the window. Water that descends in this fashion has the tendency to follow narrow paths and carve grooves into the glass surface. These grooves are formed in a process similar to canyon formation.
Silica haze – Once the silica gel has been saturated, it will be eroded by passing air currents and accumulate as white “snowflakes” on the window surface. It is believed that if this damage is present, the window must be replaced.
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