A Guide to Window Seals

If you have ever tried to wipe away fog that turned out to be inside the glass, you have met a failed window seal. Here is what is going on and how it gets fixed.

1How a double-pane window is built

A double-pane window, also called an insulated glass unit, has two panes of glass with a spacer around the edge. The edge is sealed so the space between the panes stays dry, and it is often filled with an insulating gas such as argon. That sealed space is what slows heat moving through the glass.

2Why window seals fail

• Age. Every seal wears out eventually.
• Heat and sun. Daily expansion and contraction slowly works the seal loose.
• Standing water. Water that sits at the bottom of the frame attacks the seal.
• Harsh cleaning. Pressure washers and strong solvents at the edges can damage it.
• Install issues. A unit that was set without proper support can be stressed from day one.

3What fog between the panes means

When the seal fails, moist air gets inside. On cool mornings that moisture condenses as fog, and over time it can leave a milky haze or mineral spots. Because it is inside the sealed unit, no amount of cleaning will reach it. The insulating gas may have escaped too, so the window does not insulate as well as it used to.

4Other signs of a broken seal

• A milky haze that won’t wipe off from either side.
• Droplets or streaks between the panes.
• A room near the window that is harder to keep cool.
• A slight draft or cold spot near the glass.

5How a failed seal gets fixed

The reliable fix is to replace the sealed glass unit. If the frame is in good shape, we measure the opening, order a new unit made to size and swap it in. It is often a lot less than a new window. Services that drill and dry the unit can improve how it looks for a while, but they do not restore the seal.

At NB Glass we measure in person, explain whether you need repair or replacement, and give you a clear quote before any work starts. Estimates are free, and we reply the same day.