Guide
Misted double glazing: repair or replace, and what it costs
Updated
Condensation between the panes means the sealed unit's edge seal has failed and the unit is finished as an insulator. The frame is usually fine, and that distinction is worth hundreds of pounds per window.
Your options, priced
| Option | Typical cost | Verdict |
|---|---|---|
| Replace the sealed unit only, keep the frame | £60–£200 per unit | The standard fix for a sound frame |
| Drill-and-dry "demisting" services | Less than a new unit | Clears the fog but the failed seal remains; results and longevity are mixed |
| Replace the whole window | Several times the unit price | Only worth it when the frame itself is failing, or as a planned upgrade |
These are typical 2026 quote ranges. Unit price depends on size and specification: a small casement pane sits near £60, a large low-E argon-filled unit with toughened glass near £200 or above. Every unit is made to measure, so expect a measuring visit, then fitting roughly a week later (typical lead time, varies by supplier).
Why units mist
A double-glazed unit is two panes bonded to a spacer bar with desiccant inside. When the perimeter seal fails, moist air gets in, the desiccant saturates, and water vapour condenses between the panes where no cloth can reach. It is a wear item: seals age with sun and movement, which is why misting usually appears on the sunniest elevations first.
Repair, replace the unit, or replace the window?
- Frame sound, one or two misted units: replace the units. It is the cheapest real fix and restores the insulation.
- Drill-and-dry demisting: a lower-cost cosmetic option; the fog clears, but the unit has still lost its sealed gas fill and the failure that let moisture in remains. Treat claims of like-new performance with caution.
- Several failed units on old frames: price both routes. When half the house has failed units and the frames are 25 years old, whole-window replacement with modern glass can be the better spend, see is A-rated glass worth it.
- Replacing a unit is generally a repair, so it does not usually trigger the certification that whole-window replacement does (see the Building Regulations note in the A-rated guide).
Getting a fair price
- Count the misted units and measure roughly; per-unit prices drop when several are done in one visit.
- Ask what glass is included: low-E and argon fill are standard in a decent replacement unit, not extras.
- Get more than one quote, the form takes two minutes and local glaziers price the actual job.