Misted Double Glazing: Why It Happens, What It Costs to Fix, and When to Replace Instead

What "misted" actually means

If there's a permanent haze, fog, or streaks trapped between the two panes of a double-glazed window, no amount of cleaning will get rid of it. That's different from ordinary condensation on the inside of the glass, which comes and goes with the weather and wipes away.

A sealed double-glazed unit works because there's a thin gap between the two sheets of glass, filled with air or argon gas, with a desiccant strip around the edge that keeps that gap bone dry. When the seal around the edge fails, usually because of age, movement in the frame, or a manufacturing fault, moist air gets in. The desiccant can only absorb so much before it's saturated, and once it is, you get permanent misting, sometimes with mineral streaks or a cloudy film that never clears.

It's extremely common. If your windows are more than 10 to 15 years old, a failed seal on one or two units somewhere in the house is close to inevitable.

Why it happens

A few things drive seal failure. Age is the biggest one: most manufacturers guarantee a sealed unit for 10 years, and plenty fail well before that while others go on for decades. A unit that went in slightly out of square puts constant stress on the seal from day one. uPVC and timber frames also expand and contract with temperature, and enough of those cycles work a seal loose over the years. Sometimes it's simpler than that: the unit was never sealed properly at the factory and fails within a year or two. And occasionally it's a knock, a slammed door, or a poorly fitted trickle vent cracking a seal that was otherwise fine.

None of these mean the window itself is failing. In the vast majority of cases the frame, the hinges, and the locking mechanism are all still doing their job. It's the sealed glass unit on its own that's gone.

Can misted double glazing be repaired?

Yes, in almost every case. You don't need a new window. You need a new sealed unit fitted into the existing frame, which is a straightforward glazing job rather than a full installation.

The process: we measure the failed unit, order a new sealed pane to match (same thickness, same gas fill, same Low-E coating if the original had one), remove the beading around the frame, lift the old misted unit out, drop the new one in, and re-fit the beading. Most single-window jobs take under an hour once the replacement glass is on site.

The only cases where repair isn't the right call:

• The frame itself is rotten, warped, or cracked
• The window is genuinely at the end of its life and other faults are stacking up (failing locks, perished gaskets, draughts)
• The glass spec is obsolete and a like-for-like match isn't available, which sometimes applies to older leaded or textured units

If none of those apply, replacing the pane is nearly always cheaper and just as effective as a new window.

What does it cost to fix misted double glazing?

As a general guide for Stockport, Manchester and Cheshire:

Prices vary with pane size, glass spec, and how accessible the window is. A ground floor casement is quicker and cheaper than a large upstairs bay. We always survey and give a fixed price in writing before any work starts, so there's no surprise on the day.

Is it worth repairing, or should you replace the whole window?

Run the numbers before you decide. A misted unit repair at £80 to £180 versus a full window replacement at £450 upwards is not a close call if the frame is sound. Replace the whole window only when the frame has its own problems that the glass repair won't touch.

A quick way to check: open and close the window. If it operates smoothly, locks properly, and sits flush in the frame with no draughts, it's almost certainly just the glass that's failed and a pane replacement is all you need. If the window feels loose or draughty, or the frame shows rot or warping, get that one looked at properly rather than just swapping the glass.

What happens if you leave it?

A misted unit won't fix itself and won't stay the same. Over time:

• The insulation value of the window drops, since the trapped gas or air layer that keeps heat in has been compromised
• Mineral deposits and streaking inside the unit tend to get worse, not better
• On older units, moisture ingress can eventually affect the frame and seals around the glass, turning a simple pane swap into a bigger job

It's not urgent the way a broken lock is. But it doesn't get better on its own, and most homeowners end up fixing it once the fog starts bothering them, or once they notice the room isn't holding heat the way it used to.

Frequently Asked Questions

Can misted double glazed windows be repaired, or do I need a new window?

Repaired, in almost every case. The frame, hinges and locks are usually fine. It's the sealed glass unit that's failed, and that can be replaced on its own without touching the rest of the window.

How much does it cost to fix a misted double glazed window?

Typically £80 to £180 for a standard single pane in Stockport and the surrounding area, more for larger panes or patio door panels. We give a fixed written quote after a free look at the job.

Why do double glazed windows mist up between the panes?

The seal around the edge of the unit has failed, letting moist air into the gap between the two panes. It's usually down to age, frame movement, or the original seal not holding, and it happens on a lot of houses once windows pass the 10 to 15 year mark.

Why is my window misted on the outside only?

That's usually ordinary surface condensation, not a failed seal, especially on cold, still mornings. It happens when the outer pane is colder than the air around it and clears on its own once the temperature evens out. Misting trapped between the two panes, which won't clear, is the sign of an actual seal failure.

Do you charge for a quote on misted window repairs?

No. Diagnosis and a written quote are free within our normal Stockport, Manchester and Cheshire service area.