Have you noticed a cloudy or foggy haze on your window that no amount of inside or outside cleaning will remove? The problem is moisture between double or triple glass panes, typically due to a broken window seal.
A number of factors can cause window seal failure, including improper installation, degradation from dirt and debris, high winds, or in the case of southern facing windows, the constant exposure to heat from the sun. The sun’s heat can actually can the cause the sealant in window seals to harden and crack. In double pane windows, the air between the glass panes heats up and causes the sealed window unit to expand and push air out through the compromised seals. After sunset, the window cools and contracts, drawing in air and humidity. Overtime, as this cycle continuously occurs, the window seal is stressed and the space between the glass fills with moisture or fog.
Why are there multiple glass panes? The idea behind insulated or double pane glass is to reduce homeowner’s energy costs. Since glass alone is not effective as an insulator, the space between the glass panes needs to be filled with an inert gas such as argon, xenon, and krypton. Since it has a 34% lower thermal conductivity rate than the normal atmosphere, Argon is the preferred choice.
Silica desiccant is an agent that is placed in window glass assemblies to absorb the moisture that can be drawn into the window. Unfortunately this material has a limited capacity and once it becomes saturated it is no longer effective.
If window fog occurs in multiple windows, and the windows are over 10 years old, the best recourse is probably to replace the windows. If your windows are very old, you may actually enjoy some energy savings to offset the cost of the new windows. If your budget will not allow replacement, or fogging is only noticed in a few windows, seal repair might be an option.
The best case scenario is to prevent a broken window seal by keeping up with proper maintenance. Keep windows clean and closely inspect seals every couple of years to see if re-caulking is needed.