Fogged Windows in the House: Causes and Solutions

You wake up on a cold morning and notice that you have fogged windows. You wonder – is this a cause for concern?

The truth is, sometimes, a little fog on the outer panes of window glass is nothing more than condensation build-up. But if you see moisture in between the window panes, it might be time for a replacement.

Fogged Windows in the House: Causes and SolutionsView in gallery

Here’s what you should know about fogged windows and how to fix them.


Top Causes of Fogged Windows

Fogged windows are the result of condensation build-up. Condensation occurs if the air inside is warm and the air outside is cold, or vice versa. The competing temperatures meet at the window, causing a little fogging. 

When fogging occurs outside the glass, it’s not a significant cause for concern. You can do several things to fix it, like monitoring humidity levels. 

But, when the fogging happens between the glass panes, you have a bigger issue.

Most modern windows have glass called an Insulated Glass Unit, or IGU. The IGU contains 2-3 panes of glass, separated by a spacer and sealed tight. Sometimes there’s an insulating gas added between the panes.

When you notice fogging inside the panes, your seal has broken, and the window is no longer insulative. Depending on the manufacturer, you can expect a seal on a thermal window to last 10-20 years.

Without the seal, the window becomes a weak point where air can leak. And, if you have wooden windows, the constant fog can lead to rot, mold, and decay.


Three Ways to Fix a Fogged Window 

When your window begins to fog between the panes, it’s ready to be replaced. Here are your options.

Replace the Entire Window

If your glass is fogging and your window has other issues, like not shutting all the way, it’s time for a replacement.

If only one window is affected, contact your window manufacturer to inquire about a replacement. (The window may still be under warranty if purchased within the last 10-15 years.)

The cost to replace a window depends on its size, style, and customization. For example, the average replacement cost for a standard double-hung window is $600. Although, depending on the frame, the price can be as low as $100.

If you have a double-hung, single-hung, or sliding window, you can replace the broken sash rather than the entire unit.

Replace the IGU

The IGU is the sealed glass unit in your window. If your frame is in great shape and you’re dealing with one defective window, IGU replacement is the best option.

Replacing the insulated glass unit is an intricate process, best left to professionals. Contact your local glass repair shop. They’ll be able to order and install the correct IGU on your behalf.

The cost of replacing your glass depends on the size and shape of your window and its customizations. It’s reasonable to pay $10-$20 per square foot for replacement double-pane thermal glass.

Defog and Reseal the Window 

Your last option is to defog the window and reseal it. Even if you do this, your window will be less energy efficient. But, it is a less expensive way to fix the cosmetic issues of fogging.

Here’s what happens during window defogging:

  • A professional drills two tiny holes into the window glass near the bottom of the pane. Then, a cleaning solution goes inside the panes to help eliminate the fog (moisture), or you can run a dehumidifier beside the windows.
  • Once the fog is gone, which can take days, the window repair person will spray an anti-fog solution inside the glass.
  • Then they’ll add small vents to the glass (via the holes) and use clear silicone caulk to seal the windows.

What Happens When You Don’t Fix a Foggy Window

Fog between window panes is moisture that can’t escape. Depending on your frame material, the moisture can lead to mold, mildew, rot, and decay. Your windows also remain much less energy efficient.