Fog between the panes means the seal on your insulated glass unit has failed. The window isn’t dirty — it’s broken, and no amount of cleaning reaches the moisture, because it’s sealed inside the glass. You can sometimes replace just the glass unit and keep the existing frame. But if the frames are aging or several windows have fogged, replacing the whole unit usually delivers better long-term value.

What does fog between the panes actually mean?

A modern window isn’t one sheet of glass. It’s an insulated glass unit — two or three panes bonded around a spacer, with the gap filled by argon or krypton gas and a desiccant strip inside the spacer to absorb stray moisture.

That assembly is sealed. When the seal fails, two things happen at once: the insulating gas escapes, and humid outside air works its way in. The desiccant absorbs that moisture until it’s saturated — often for years — and then it gives up. The day you first notice fog is not the day the seal broke. It’s the day the desiccant ran out.

This is why cleaning does nothing. The moisture is inside a sealed cavity you cannot reach without breaking the unit apart.

Why do window seals fail so often around Puget Sound?

Seal failure is driven by movement, and movement is driven by temperature swings. Our climate is unusually good at producing them.

  • Daily swings on sun-facing walls. A south or west elevation can heat hard in the afternoon and drop sharply after sunset. The glass expands and contracts with it, and the seal flexes every cycle.
  • Persistent moisture. Eight months of wet weather means any compromised seal has constant humidity pressing against it.
  • Wind-driven rain. On exposed sites — waterfront, hillsides, anything facing the Sound — water is pushed at the glass edge rather than running down it.
  • Age. Many South Hill homes were built in the 1980s through early 2000s. The original builder-grade units in those houses are now reaching the end of their service life more or less on schedule.

Seal failure is a wear-out mode, not a defect. It’s what insulated glass does eventually.

Can a foggy window be repaired?

There are three real options, and they’re genuinely different in what they solve.

  • Replace the insulated glass unit only. The sash and frame stay; only the glass assembly is swapped. This is a legitimate repair and the right call when the frames are sound and the hardware still works well.
  • Replace the whole window unit. New frame, new sash, new glass. This is the right call when frames are tired, hardware is failing, the window is single-glazed elsewhere in the house, or several units have gone at once.
  • “Defogging.” A hole is drilled, the cavity is cleared and vented. Treated as a repair, it disappoints — see below.

Does window defogging actually work?

It clears the view. It does not restore the window.

Defogging removes the visible moisture but does not re-seal the unit or replace the lost insulating gas. What you’re left with is a clear window that performs closer to plain double glazing than to the sealed unit you started with — and because the cavity is now vented, moisture can return in humid conditions.

If your goal is cosmetic and you’re selling next month, it’s defensible. If your goal is a window that insulates, it isn’t a fix.

Should I replace just the glass, or the whole window?

Answer these honestly and the decision usually makes itself:

  • How old are the frames? Glass-only replacement puts new glass in an old frame. If the frame has ten years left, you’ll be back.
  • How many windows have fogged? One is bad luck. Four or five is a batch of units reaching end of life together, and the rest are likely close behind.
  • Does the hardware still work? Locks, balances and cranks that are stiff or broken won’t be improved by new glass.
  • Is the frame itself sound? Rot at the sill, or a vinyl frame that’s distorted, rules out glass-only work.
  • Are you fixing anything else on that wall? If siding or trim is coming off anyway, replacing full units while the wall is open is far more efficient than doing it twice.

Is a foggy window still insulating my house?

Partially — and less than it looks.

Once the seal fails, the argon or krypton fill escapes and is replaced by ordinary air. The window still insulates better than a single pane, because you still have two panes and an air gap, but it no longer performs to the rating it was sold at. Any low-E coating on the inner surfaces can also degrade once moisture reaches it.

In practice you get a colder pane, more condensation, and a room that’s harder to keep comfortable — most noticeably in the months you care about it most.

What does it cost to fix a foggy window?

As a general market observation rather than a quote: replacing an insulated glass unit alone typically costs less than replacing a full window, but the gap narrows once labor, access and any frame repair are accounted for. Across several windows, the per-window difference often shrinks to the point where full replacement is the better value — particularly if the existing frames are near end of life.

Prices vary widely by size, glass specification, frame material and access, so treat any number you read online as a range rather than a figure for your house. For how exterior project pricing works in this area generally, see our Puyallup and Pierce County cost guide. For your own windows, we’ll look and tell you which of the three options actually makes sense — including when the answer is “leave it for now.”

Common questions about foggy windows

Can I replace just the glass and keep my existing frames?

Often yes, if the frames are structurally sound and the hardware works. It’s a real repair, not a shortcut. It stops making sense when the frames are near end of life, since you’d be installing new glass into something you’ll replace in a few years anyway.

Does defogging permanently fix a foggy window?

No. It clears the moisture you can see but doesn’t re-seal the unit or restore the insulating gas that escaped. The view improves; the insulating performance doesn’t come back, and fog can return in humid weather.

Is a fogged window covered by a manufacturer warranty?

Sometimes. Many insulated glass units carry a manufacturer warranty against seal failure, often with a defined term and frequently limited to the glass rather than labor. Coverage depends on the manufacturer, the age of the unit, and whether the original documentation and ownership records exist. It’s worth checking before paying for anything — we’ll help you look.

Why did only one of my windows fog up?

Usually exposure. The unit taking the most direct sun, the most wind-driven rain, or the sharpest daily temperature swing fails first. It’s often the leading edge of a batch rather than an isolated fault — if the rest were installed at the same time, keep an eye on them.

Is condensation on the inside surface of the glass the same problem?

No, and this distinction matters. Moisture you can wipe off the room-side surface is indoor humidity meeting cold glass — a ventilation and humidity issue, not a broken window, though it does tell you the glass is running cold. Fog you cannot wipe off, because it’s between the panes, is seal failure.

Will a foggy window get worse over winter?

Typically yes, and it’s usually when people notice. Colder glass and higher indoor humidity make the fogging more visible, and repeated freeze-and-thaw cycling at the glass edge doesn’t help a seal that has already failed. It won’t become dangerous, but it will become more obvious and the pane will run colder.

Get a straight answer on your windows

We’ll tell you whether you’re looking at a glass swap, a full replacement, or a window that’s fine to leave alone for another few seasons. If it’s not worth doing yet, we’ll say so. Call (253) 365-9322 or use the form below for a free assessment anywhere in the South Sound.

Every job we install carries our 2-year workmanship warranty, plus the manufacturer’s own warranty on the products themselves.

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