Condensation between the panes — fog you cannot wipe off from either side — means the sealed glass unit has failed. It is the single most common window problem we are called about, and the first question is always the same: can it be fixed, or do I need a whole new window? After 5,247 installations since 2003, here is the honest decision guide, with real 2026 prices for both routes. And full disclosure up front: we are a whole-window installer, so where a glass-only swap is genuinely the right answer, we will say so.
The short answer: A misted unit can be repaired by replacing just the sealed glass — €150–€250 + VAT per pane — which makes sense when the frames are under 15 years old and in good condition. Replace the whole window (from €600 + VAT fitted) when frames are warped, draughty or pre-2011: that route is A-rated, comes with a 10-year guarantee, and qualifies for the SEAI grant of €1,500–€4,000 — glass-only swaps do not.
What is a misted or failed double-glazed unit?
A double-glazed unit is two panes of glass factory-sealed around a spacer bar, with argon gas and a desiccant inside the cavity. The edge seal keeps moisture out and the argon in. When that seal perishes — typically after 15–25 years — moist air creeps in, the argon escapes, and condensation forms inside the cavity where you cannot reach it. The tell-tale signs: fog or water droplets between the panes that come and go with the weather, a milky haze that never clears, or visible water pooled at the bottom of the unit. Once it starts, it only gets worse — there is no drying-out fix.
Why sealed units fail in the Irish climate
- Age: most failures happen between years 15 and 25 — the sealant simply reaches the end of its life.
- Exposure: south- and west-facing windows take the brunt of Irish sun-cycles and driving rain, which expand, contract and soak the edge seals year after year. These panes nearly always fail first.
- Poor drainage: units sitting in trapped water inside a badly drained frame fail years early — the seal was never designed to be submerged.
- Original quality: budget units from the 1990s-2000s double-glazing boom used narrower spacer bars and cheaper sealant. Many are failing right on schedule now.
Repair or replace — the honest decision guide
There are only two real options: swap the sealed glass unit into your existing frame, or replace the whole window. Neither is always right — it depends on the frame:
| Situation | Right call | Typical cost |
|---|---|---|
| Frames under 15 years old, square, draught-free, good hardware | Replace the glass unit only | €150–€250 + VAT per pane |
| One or two failed panes in an otherwise sound window set | Glass-only swap | €150–€250 + VAT per pane |
| Frames warped, rotten, discoloured, or draughty when closed | Full window replacement | From €600 + VAT per window fitted |
| Several units failed across a pre-2011 home | Full replacement + SEAI grant | €6,000–€12,000 minus €1,500–€4,000 grant |
| Unit failed inside its manufacturer guarantee (usually 5–10 yrs) | Claim on the guarantee first | €0 if in warranty |
One honest note: Airtight is a whole-window and door installer — for a single glass-only swap on a young frame, a local glazier is usually the cheaper and faster route, and we will tell you that on the phone. Where we add value is the full replacement: A-rated frames and glass together, fitted by our own team, with the 10-year workmanship guarantee and the SEAI grant handled with you.
Does the SEAI grant apply?
Only to whole-window replacement — not to glass-only repairs. The SEAI windows and doors grant pays a fixed amount by home type (€1,500 apartment · €1,800 mid-terrace · €3,000 semi · €4,000 detached) when an SEAI-registered installer fits A-rated windows in a pre-2011 home. That changes the maths significantly: a semi with eight failed units costs roughly €1,200–€2,000 for glass-only swaps that still leave you with 20-year-old frames — versus around €6,000–€8,000 for full A-rated replacement minus the €3,000 grant, with new frames, new locks and a fresh 10-year guarantee. Check your eligibility in five minutes on our grant eligibility checker.
The bottom line
One misted pane in a young, sound frame? Swap the glass for €150–€250 and move on — a glazier is your best value. Frames past their best, multiple failed units, or a pre-2011 home? Replace the windows properly and let the SEAI grant take €1,500–€4,000 off the bill — see our 2026 window prices for per-style figures and A-rated double glazing for the spec. Owen responds within 24 hours, tells you honestly which route your windows need, and arranges a free survey.