Misted double glazing: what it really costs to fix
Last reviewed: July 2026 · Fitted prices incl. VAT
Condensation trapped between the panes — “misted”, “blown” or “fogged” glazing — is the most common double glazing failure in the UK, and the most profitably misdiagnosed. It means the sealed glass unit has failed, not the window. A glazier can replace just the unit for £75–£200 per window, while a salesperson would rather quote you £450–£750 for a whole new one. This guide is the difference.
What actually failed (and why it matters)
A double-glazed “sealed unit” is two panes bonded around a spacer bar filled with desiccant, sealed at the perimeter. When that perimeter seal perishes — age, sun, movement in the frame — moist air creeps in, the desiccant saturates, and water vapour condenses on the inside faces of the glass where no cloth can reach. The frame, hinges and handles are usually still fine. That is why the fix is a glass swap, not a window swap: the glazier measures the unit, has a replacement made, and fits it into your existing frame in under an hour per window.
Replacement unit costs
| Job | Typical fitted cost |
|---|---|
| Misted / blown sealed unit (glass only, standard size) | £75 – £200 |
| Perimeter rubber seal / gasket replacement | £50 – £130 |
- Size is the biggest driver — a small top-opener sits at the bottom of the band; a patio-door-sized pane can exceed it.
- Glass spec adds cost — toughened (required near floor level and in doors), obscured, acoustic or self-cleaning glass all price higher than standard.
- Access matters — ground floor is straightforward; anything needing ladders or scaffold moves the price up.
- Upgrading while you are there is cheap — a modern A-rated unit in place of a 20-year-old one improves insulation for little or no extra cost.
When it IS time to replace the whole window
- The frame has failed — warped, cracked, rotten, or the unit keeps blowing because the frame no longer drains properly.
- Multiple units gone across the house — several £75–£200 repairs start to compete with a whole-house price that also buys new frames and a fresh guarantee. Our replacement cost guide has the numbers.
- Very old units — pre-2002 glazing predates modern efficiency standards; if you are fixing more than one thing per window, replacement usually wins.
The working rule from our repairs guide applies here too: if the repair bill passes half the cost of replacement, replace.
Frequently asked questions
Why has my double glazing misted up between the panes?
The sealed unit has failed. Every double-glazed unit has a perimeter seal and a desiccant that keeps the gap between the panes dry. When the seal perishes, moist air gets in, the desiccant saturates, and condensation forms inside the glass where you cannot wipe it. It is a glass problem, not a frame problem.
How much does it cost to replace a misted double glazing unit?
Typically £75–£200 per unit fitted for a standard-size window — the glazier replaces just the sealed glass unit and keeps your existing frame. Very large panes, obscured or toughened glass, and hard-access upper floors push the price toward the top of the band.
Can misted double glazing be repaired without replacing the glass?
There are drill-and-dry "demisting" services that vent the unit and clear the visible condensation. They can improve the appearance for a while, but the failed seal and saturated desiccant remain, so the misting frequently returns. Replacing the sealed unit fixes the actual fault and restores the insulating gap.
Does misted glass mean I need new windows?
Usually not. If the frames are sound, swapping the sealed units costs a fraction of full replacement. New windows only become the better call when the frames themselves have failed, or when so many units have blown that per-unit costs stack up against a whole-house price.
Sources: repair and replacement cost bands compiled July 2026 from published UK glazier and installer price guides (Checkatrade, Which? Trusted Traders data), cross-checked against regional quote data.