Blown window repair Cost Calculator
A blown window — condensation trapped between the panes — means the sealed unit has failed, not the window. Replacing just the glass unit costs £75–£250 fitted for most casements, rising to £200–£450 for toughened patio-door glass. The frames stay…
Open the calculator →Price blown window repair in 30 seconds
3 steps, using the figures from our cost guide.
How this calculator works
Every figure in this calculator is the one published in the cost table on our blown window repair guide. Pick the option that matches your job and the calculator returns that published range, adjusted for your region - it does not model anything the guide does not already say.
That is deliberate. A calculator whose rates drift from the page it sits under is worse than no calculator, because two numbers on the same site disagree.
What it cannot know: access, the condition of what is already there, and anything structural. Those are what separate three real quotes from each other.
Published blown window repair costs (2026)
| Option | Typical 2026 cost | Notes |
|---|---|---|
| Small casement unit (to ~0.5m² | £75–£150 | |
| Standard casement unit | £100–£200 | |
| Large fixed / picture unit | £150–£300 | |
| Patio door glass (toughened) | £200–£450 | |
| Bay window (3–5 units) | £300–£850 | |
| Whole-house refresh (8–12 un | £700–£1,900 |
These are the figures from our blown window repair cost guide.
What actually moves a blown window price
The price of a blown unit turns on the glass, not the frame. A standard clear double-glazed unit is cheap to make; the cost climbs with size and with the spec - toughened glass for doors and low-level panes, obscure or patterned glass for bathrooms, and low-emissivity coatings or coloured spacer bars to match what is already there. The published blown window repair cost guide lists the per-unit ranges this calculator draws on.
Access is the other half of the bill. A ground-floor casement you can reach from a stepladder is a quick swap; a first-floor unit over a bay, a rooflight, or anything that needs a tower or scaffold adds a fixed cost before the glass is touched. Fitters also charge less per unit when several are done in one visit, which is why a whole-house refresh works out cheaper per window than a single call-out.
Two things are worth checking before you book. If the frames are sound a unit swap is the sensible fix, but perished gaskets or warped frames mean the new glass will fail early - at that point a full window makes more sense, and our double glazing cost guide is the better read. If several windows have blown at once it is usually age rather than bad luck, and the double glazing hub lists installers who will assess the whole house rather than sell you one unit at a time.
Blown window repair calculator — FAQs
A double-glazed sealed unit whose edge seal has failed. The desiccant in the spacer bar saturates, moisture creeps between the panes and shows as misting or droplets you cannot wipe off. The glass unit needs replacing; the window itself usually does not.
“Demisting” services drill the unit and vent or flush it for £60–£120. It clears the visible mist for a while, but the seal is still failed and the insulating gas is long gone — most units mist again. Treat it as a cosmetic stopgap, not a repair.
When the frames are sound, yes — a unit swap typically costs £75–£250 against £400–£1,800 for a full new window. When gaskets are perished or frames warped, the new unit will fail early and full replacement is the honest advice.
Two visits: one to measure, then about an hour per unit to fit once the made-to-measure units arrive — usually one to two weeks later. Beads are removed, the unit swapped and the window back in use the same hour.
Usually, yes. A fitter measures the unit and notes the spec - clear or obscure, toughened or not, the coating and the spacer colour - so the replacement matches its neighbours. Older or unusual patterned glass can be harder to source and may add a little to the price or the lead time, so flag any obscure or decorative panes when you ask for a quote.
Related cost guides
- Blown window repair cost guide — The full price guide
- All double glazing services — Browse the hub
- All BestBuilders services — Every trade we cover
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