Quick answer: Repairing a misted-up double glazed window — replacing just the sealed glass unit, leaving the frame in place — costs £40 to £80 per pane for a standard size, fitted by a glass-only specialist. Replacing the whole window (frame + glass) costs £300 to £700 per window in 2026 UK pricing. This guide explains which option makes sense for your situation, who can do the work, and what to watch out for.
What “misted” actually means
A double glazed window contains two panes of glass separated by a sealed gap (filled with argon or air). The perimeter is sealed with a butyl + secondary-seal system designed to last 15–25 years. When that seal fails, three things happen:
- Moisture gets in from the outside, hits the cold inner pane, and condenses as visible mist or water droplets you can’t wipe away.
- The argon escapes, replaced by ordinary air with much worse insulation.
- Your window’s U-value collapses — typically from 1.4 W/m²K (modern A-rated) to about 2.8 W/m²K — closer to single glazing than to working double glazing.
The frame is usually fine. The glass-only “insulated glass unit” (IGU) inside it is the part that’s failed. This matters because it’s the difference between a £40 fix and a £600 replacement.
Your three options at a glance
| Option | Typical UK cost | How long | When it makes sense |
|---|---|---|---|
| 1. Ignore it | £0 upfront, ~£60–£120/year extra heat loss | Until you sell | You’re moving in 12 months and the window doesn’t fog the view |
| 2. Replace the glass unit only | £40–£80 per pane (standard size) | 1 visit, 1 hour per window | Frames look fine, ≤3 windows affected, windows under 20 years old |
| 3. Replace the whole window | £300–£700 per window | 1–2 days for a typical house | Frames cracked/discoloured, hardware failing, or 5+ windows misting at once |
Option 2 — Replace just the glass unit (the cheap fix)
What it costs
- Standard small window (up to ~0.5m²): £40–£60 per pane, supplied and fitted
- Medium window (0.5–1.0m²): £55–£85 per pane
- Large window or door panel (over 1.0m²): £80–£140 per pane
- Toughened or laminated glass (required at low level by Building Regs Part K): add £20–£40
- Argon refill, low-E coating: built into the price for any modern unit
- Call-out fee (most specialists waive this if you book 2+ windows): £25–£40
Total for a typical 3-bed semi with 4 misted windows: roughly £200–£300 if booked together.
How the process works
- You measure each misted unit (or the specialist measures during a free survey).
- They order a custom-cut sealed unit to those exact dimensions — typically 5–10 working days lead time.
- One install visit, ~30–60 minutes per window. They take out the glazing beads, lift out the failed unit, drop in the new one, re-bead, gone.
- Frame stays put. Hardware untouched. No making good or redecoration.
When this is the right call
- You can see the misting but the frame is in good cosmetic and structural condition
- Hinges, locks and handles all still work properly
- The window is under 20 years old — same-spec replacement units are still made
- Only 1–4 windows are affected (above that, full replacement starts to win on cost-per-unit and warranty)
Option 3 — Replace the whole window
What it costs
- Standard uPVC casement (1.0m²): £300–£500 supplied and fitted, FENSA-registered
- uPVC sash window: £700–£1,200
- Aluminium casement: £550–£900
- Whole 3-bed semi (typically 8–10 windows): £4,500–£8,000 — more if it’s heritage glass or large openings
Use our cost calculator for a precise estimate based on your home’s size and postcode.
When this is the right call
- Five or more windows are misting — you’ll save by buying a whole-house package vs four separate IGU repairs
- Frames are cracked, discoloured, or warping
- Hinges, locks or handles are also failing
- Windows are over 25 years old — modern A-rated units cut your heating bills enough to pay back the upgrade in 8–12 years
- You’re upgrading to triple glazing or larger openings — full replacement is the only path
Decision tree — repair or replace?
Walk through these questions in order:
- How many windows are misting? 1–4 → repair likely cheaper. 5+ → full replacement starts to win.
- How old are the windows? Under 20 years → repair viable. Over 25 → full replacement makes more financial sense.
- Are the frames also failing? Yes → full replacement (no point repairing glass in a frame that’s about to go).
- Do you plan to sell within 2 years? Yes → repair only the most visible windows. Full replacement won’t pay back unless your buyers actively price it in.
- Are you upgrading to A-rated or triple glazing? Yes → full replacement is the only route.
Who can do the repair?
Three types of trades can replace sealed units:
- Glass-only specialists — usually the cheapest (£40–£80 per pane). Look for businesses that say “sealed unit replacement” or “blown window repair” specifically. Often local one-or-two-person operations.
- FENSA-registered window installers — typically £20–£40 more per pane than glass-only, but they handle full replacement too if needed. Worth using for ≥4 panes when you’re not sure repair is enough.
- Handymen / general builders — avoid for sealed unit work. The IGU has to seat correctly on packers and the glazing beads need precise refit; getting it wrong shortens the new unit’s life dramatically.
For background on the difference between FENSA and other certification schemes, see our FENSA vs Certass vs Trustmark guide.
Warranty pitfalls
- Glass-only repairs don’t extend the original window warranty. The new unit gets its own (typically 5–10 year) guarantee on the seal failing again, but the frame and hardware are still on their original clock.
- Cheap units skip the desiccant or use a butyl-only seal. Industry-standard is a dual-seal system with desiccated spacer. Ask explicitly: “Is this a dual-sealed unit with warm-edge spacer?” If they don’t know what that means, find someone else.
- Warranty is only as good as the company. If a glass-only specialist disappears in 3 years and your repair fails in year 4, that warranty is worthless. For peace of mind on big jobs, prefer a FENSA-registered installer who carries an Installsure insurance-backed guarantee.
- Original-window warranties usually don’t cover sealed unit failure beyond year 5 — even if the frame’s lifetime warranty is 10 or 25 years. Read the small print before assuming you’re covered.
Frequently asked questions
How do I know if my window is misted vs just dirty?
If you can wipe it off from either side of the glass, it’s dirt or surface condensation. If the haze or droplets are between the panes and you can’t reach them, the seal has failed. That’s a misted unit.
Can I repair a misted unit myself?
No. The sealed unit has to be ordered to exact dimensions and seated correctly with the right packers and beads. DIY usually fails within 2 years. Cost difference vs hiring is typically £20–£40 per window — not worth the risk.
My window has a “lifetime warranty” — won’t they fix it free?
Probably not. Most “lifetime” warranties cover the frame only, with a separate (much shorter) glass-unit warranty of 5–10 years. And several major UK brands (Safestyle in 2023, Everest twice in the last decade) have entered administration — their warranties evaporated on day one. The protection that survives is your insurance-backed guarantee, not the company’s own promise. Check whether yours has an Installsure or QANW IBG before counting on it.
Will home insurance cover misted windows?
Only if the seal failure was caused by an insured event (e.g. impact damage). Standard wear-and-tear seal failure isn’t covered. Worth checking your policy before paying out of pocket.
How long does a replacement IGU last?
10–20 years for a quality dual-sealed unit with warm-edge spacer. Cheap single-sealed units can fail in as little as 5 years — a false economy.
Does replacing one misted unit affect the others?
No — each window is independently sealed. Replacing one doesn’t trigger or accelerate failure in the others.
Get a quote — repair or replacement
Tell us how many windows are misted and your postcode. We’ll connect you with up to 4 vetted local installers — both glass-only specialists and FENSA-registered window companies — within 24 hours. Free, no obligation, no pressure.
Want a budget figure first, no contact details required? Try our cost calculator for a 30-second estimate.
Sources used: Checkatrade misted DG repair cost guide (2026), MyJobQuote condensation removal cost data, MyBuilder blown DG repair price guide, Eco Experts condensation guide, Glass and Glazing Federation specifications, Installsure insurance-backed guarantee terms (2026). Pricing is UK 2026 estimate. Last reviewed: April 2026.
From homeowners like you
Tenement flat in the West End — a lot of installers wouldn't quote because of access, but Findfitter matched me with one who specialises in G1-G3 flats. Spot on.
Quick, clear, no pressure. I asked the 6 questions from the buyer's guide and it genuinely filtered out the weaker installers. Picked the local one with the longest track record.
Replaced 8 windows in our 1930s semi in Didsbury. Quotes came within 6 hours. Winter gas bill is down about 38%. Fitter was spotless and finished in a day and a half.