A double pane window that looks foggy, cloudy or crusty between the two panes has a failed seal. It is the thing people most often mistake for dirty glass, and it is the one thing a window cleaner cannot clean, because the mess is sealed inside the window. Once both sides of the glass are properly clean, a failed seal is easy to spot.
What a failed seal looks like
The giveaway is that the marks do not move when you clean. Look for any of these:
- A haze or fog that is still there after both sides of the glass have been wiped.
- Droplets between the panes, often worse in the morning or after rain, while the outside of the glass is dry.
- White spots, streaks or a crusty line along the bottom edge of the glass, left behind each time the trapped moisture dries.
- A pattern that changes with the weather even though nobody has touched the window.
Why seals fail in Central Texas
A double pane window is two sheets of glass with a sealed gap between them, often filled with argon gas to help insulate the house. A seal around the edge keeps air and moisture out of that gap.
Every day the sun heats the glass and the unit expands, and every night it cools and shrinks again. In Central Texas that happens hard, almost every day of the year. Over the years the seal starts to give. Once it does, humid air gets into the gap, condenses on the inside faces of the glass, and leaves minerals behind as it dries. Age is the biggest factor, and windows that take the full afternoon sun tend to go first.
Hard water or a failed seal?
Both leave white spots, so they get mixed up all the time. The difference is where the spots sit.
Hard water is on the surface
Hard water comes from sprinklers, and it sits on the outside of the glass. Run a fingertip across it and it feels rough. It usually lines up with where the water hits, which is most often the lower panes. Caught early, it comes off. There is more on this in hard water stains on windows in Central Texas.
A failed seal is inside the glass
A failed seal feels smooth on both sides, because the marks are between the panes. The simple test is to clean a small patch on the inside and the outside. If the spots are still there, they are inside the window.
Why cleaning cannot fix it
The fog is inside a sealed unit. Nothing applied to the outside of the glass reaches it, and scrubbing harder only risks scratching a pane that was never the problem. Mason cleans windows. He does not replace them.
The usual fix is replacing the sealed glass unit. In many windows the frame can stay and only the glass is swapped, which a window or glass company can quote. Before you call one, check your window warranty, because seal failure is often covered for a number of years.
Finding failed windows before you sell
Buyers and inspectors notice foggy glass, and it is a bad thing to find out about from a buyer. On a dirty window you usually cannot tell a failed seal from dust. That is why Mason checks every window during a make ready clean for realtors and marks each one that needs replacing, at no charge, so the seller knows before the listing goes live.
If you are not selling, a regular inside and outside clean does the same job. A clean pane is the only way to see a failed seal clearly.
Common questions
Can a window cleaner fix a foggy double pane window?
No. When the fog is between the panes, it is sealed inside the window, and no squeegee, scraper or cleaning product can reach it. Cleaning both sides will make the glass around it clearer, but the haze stays. The fix is replacing the sealed glass unit.
How do I know if my window seal has failed?
The haze stays after both sides of the glass have been cleaned. Other signs are droplets sitting between the panes, often worse in the morning, and white spots or a crusty line along the bottom edge of the glass, left behind as trapped moisture dries.
Is it hard water or a failed seal?
Run a fingertip over it. Hard water sits on the outside surface and feels rough, and it usually lines up with where the sprinklers hit. A failed seal feels smooth on both sides because the marks are inside the glass, and they are still there after a proper clean.
Do I need to replace the whole window?
Often not. In many windows the sealed glass unit can be replaced and the frame kept. A window or glass company can tell you which applies. Check your window warranty first, because seal failure is often covered for a number of years.
Will you point out failed windows during a clean?
Yes. Once the glass is clean, a failed seal is easy to see, and Mason will tell you which panes have gone. On a make ready clean for realtors he checks every window and marks each one that needs replacing, at no charge.
The short version
If a window is foggy, cloudy or crusty between the panes and it stays that way after both sides are cleaned, the seal has failed. No cleaning will fix it, and the usual answer is a new glass unit, which may be under warranty. If you are not sure whether you are looking at hard water or a failed seal, have the glass cleaned first. Once it is clean, the difference is obvious.