By Mr. Window in Window repair and Reuben Saltzman, Structure Tech Home Inspections
Have you ever seen a window that looks like it needs cleaning in-between the panes of glass? Does cleaning the window seem pointless? That fogging is normally a result of a bad or broken seal with multiple pane windows. A leak in the seal as small as the tip of a needle can cause a foggy window.
Some people say window manufactures build windows to naturally fail to ensure repeat business, similar to light bulbs. This failure can subsequently also be blamed on a daily occurrence of thermal (solar) pumping.
What is Thermal Pumping?
Thermal pumping is the window “breathing” throughout the day. The gas/air in-between the panes of glass gets heated and cooled through-out the day by changes in weather and HVAC systems. This expands and contracts the seals, that allows air to move in and out. The goal is to let the minimum requirement of air be transferred from the seal so no moisture enters the window.
Once the window’s seal had been ruptured to a point where air enters freely, the window will eventually take on moisture from the natural atmospheric pressure. The fog will slowly appear and get progressively worse.
Why does this happen?
Most windows older than 15 years are at a higher risk of fogging. However, I have seen windows that are less than 2 years old have fogging. Reasons are as follows:
Poor installation and damaged seals.
Low quality or replacement windows
Manufacturing Error. Even in high end windows manufactures still make mistakes when they make millions of windows a year.
What to do about Foggy Windows?
Rather than replacing the entire window, you can replace just the defective pane. Most newer double-hung windows have sashes that can be easily removed without any tools. Major manufacturers such as Pella, Anderson, and Marvin all have 20 year warranties on their glass. If a window less than 20 years old develops foggy glass, contact the manufacturer. If the window is older than 20 years, you can still replace the pane for less money than it would cost to rip out and replace the window, but you'll need a window specialist to do the work.
Some window repair companies, such as Window Medics, will alter windows with broken seals to make them look good again. This process consists of drilling a couple tiny holes in the glass, washing out the inside of the window panes to clean up the 'fogginess', and then installing tiny vents in the holes to allow the window to breath. The window will no longer be foggy, and it will stay clean. The downside to this repair is that the window will have a slightly lower insulating value than it had before the glass fogged over, but this will cost much less than replacing the window.