Knowing the Signs of Window Seal Failure




Fog is an unfortunate reality of window life. Condensation may occur everywhere there is water vapor in the air (which is everywhere), resulting in foggy windows, which may or may not be an indication of window seal failure.


Temperature differentials cause condensation as a byproduct. Warm air molecules are more loosely packed, allowing small water vapor droplets to settle into larger pockets. As heated air cools, however, the molecules huddle together, squeezing the vapor droplets together and forming visible liquid water (the temperature at which this phase change happens is called the dew point)


Condensation forms on surfaces that are much colder than the surrounding temperature. It might appear on the outside of your favorite icy drink. And it's possible that it'll appear on (or in) your windows. Should you be concerned, though?


When to worry about foggy windows

Fog can form in three locations on double (or triple) paned windows, which have two or three layers of glass (glazings) layered in between, generally with an insulating inert gas (such as argon or krypton) spread in between to assist moderate the differentials we were discussing.


  1. On the outside: This is a regular occurrence on hot, humid days when the exterior environment is significantly warmer and moister than the air-conditioned inside atmosphere of your home.


  1. On the inside: During the colder months, this phenomena is reversed, as the humidity in your home condenses on the inside of the window. The moisture condenses as fog as the chilly air outside the glass condenses (think of breathing inside your car during the winter). A dehumidifier can help to counteract this impact.


  1. Foggy windows in the middle: These are the ones to be concerned about, as they indicate window seal failure. By limiting inward or outward air seepage, the seal surrounding the window's insulating glass unit (the collective term for the window panes, the entrapped nonreactive gas, and desiccants moisture absorbers such as silica) helps maximize its overall function.


Window seal failure risk factors

Window seals can fail due to a variety of factors, including manufacturing flaws, improper installation, or negligence. But the most prevalent explanation is also the most unavoidable: prolonged exposure. Thermal pumping is the expansion and contraction of the air between the glazings of a double-paned window on any given day (picture the motion of an accordion – on mute if you like). The air expands throughout the day when it is warmer. The temperature drops at night. Over time, all of those pressure variations put a lot of stress on the window seal, causing microscopic cracks.


They won't be very bothersome at first. However, the inert gas layer will ultimately leak away, allowing outside air to enter. The extra moisture will cause the silica pellets to become saturated, causing condensation to occur. Mineral deposits can form a film of filth ("silica haze") on your windows, giving the impression that they are perpetually dirty. Riverbedding, or indentations in the glass caused by trickling water droplets, indicates that the glass is deteriorating further.


Because sun heating hastens this process, choosing an energy-efficient window with a low-emissivity (low-e) coating, a microscopically thin layer of silver oxide that filters infrared and ultraviolet radiation, is a smart option. In any case, anticipate the seals on windows in sunny places to break sooner than those in the shade.


What do about window seal failure

There are five courses of action one can take in the event of window seal failure.


  1. Insulating glass unit (IGU) replacement: Fortunately, about 3 out of 4 cases can be resolved by popping out the IGU, cleaning the frame, and inserting new glass into the vacancy. Although, this is a short-term fix with regards to the 2-3 year warranty offered on this service.

  2. Sash replacement: The sashes (the moveable pieces that hold the glass panes) may need to be demolished and replaced in some cases. Sash replacements are purchased directly from the manufacturer of your windows.


  1. Complete window replacement: In rare cases (approximately 5% of the time), the complete window, including the framing, may need to be replaced. Check out our article on insert vs. full frame window replacement for additional details.


  1. Nothing: If you live in a warmer or more moderate environment, a faulty window seal or two will have little influence on your energy expenditures. "How much do foggy windows annoy you?" becomes the question. Except on extremely hot or cold days, the haze is often so light that you won't notice it.


Do you need help determining which choice is best for you? Let Bridge City Glass help with your inquiry. Our experienced staff has decades of experience in window glass repair and replacement!


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