Foggy Windows: What a Broken Seal Means

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You wipe the window inside. You wipe it outside. And it's still cloudy. If the fog, haze or little droplets are between the two panes of glass, you've got a broken seal.

It's one of the most common window questions we get, so here's what's happening and what you can do about it.

How Does a Double-Pane Window Work?

A double-pane window, sometimes called an insulated glass unit, is two panes of glass with a sealed space between them. That space is often filled with air or an insulating gas. A spacer and seal around the edges keep the space closed off. That sealed gap is what slows heat moving through the glass.

What Does a Broken Seal Look Like?

• Fog, haze or cloudiness between the panes
• Condensation droplets inside the glass
• White streaks or mineral deposits between the panes
• Fog that comes and goes with the temperature or time of day

How do you tell it's between the panes? Wipe both sides. If the fog is still there, it's inside.

What Causes Seals to Fail?

Window seals don't last forever. Common causes:

1. Age. Seals break down over time.
2. Heat and sun. North Texas summers put a lot of stress on windows, especially on the south and west sides. Glass and frames expand and contract every day.
3. Storms. Hail and wind can stress the glass and seal.
4. Installation problems. A window that's out of square or under pressure in the opening can stress the seal.
5. Water. Water sitting at the bottom of the frame, especially with clogged weep holes, can break down the seal.
6. Manufacturing defects. Sometimes it's just the window.

Why Does a Broken Seal Matter?

A few reasons:

• Efficiency. Once the seal fails, the insulating gap isn't doing its job as well. The room may run hotter in summer and colder in winter.
• Looks. Foggy windows block the view and make a house look tired.
• It gets worse. Fogging usually gets worse over time, and mineral deposits can etch the glass so it can't be cleaned.

It's not usually an emergency the way a leak is, but it's worth dealing with.

Can a Foggy Window Be Fixed?

There are a few options, and the right one depends on the window:

• Replace the glass unit. Often, the sealed glass unit can be replaced in the existing frame. This can make sense when the frame is in good shape.
• Replace the sash. Some windows let you replace the moving part of the window.
• Replace the whole window. If the frame is damaged, warped or rotted, or several windows are failing, full replacement is usually the better long-term answer.

You'll find services online that drill and "defog" the glass. They can clean up the look, but they don't restore the original seal. Ask lots of questions before you go that route.

How Do I Know Which Option Is Right?

That's where we come in. G3 looks at the glass, the frame and the opening, checks for water damage, and talks through whether repair or replacement makes sense, without a high-pressure pitch. If you already have a retail estimate from somebody else, bring it. We're happy to look it over with you. See our windows and exteriors page.

Is Fog on the Inside of the Glass the Same Thing?

No. Condensation on the inside surface of the glass, the side facing your room, is about humidity in the house, not a broken seal. That's common on cold mornings. Read our guide to window condensation in winter to learn the difference.

Frequently Asked Questions

Got foggy windows? Call (945) 300-9018 or use the button below to get a window quote.

Keep learning: see our Windows & Exteriors page, read Hail Damage to Windows and Screens: What to Check.