Foggy window repair comes down to three options: a $75–$150 defogging that clears the fog but not the problem, a $150–$400 IGU replacement that restores full performance, or full window replacement starting at $300 when the frame is shot too. The right choice depends on frame condition and window age, plus how many panes have already failed. If you are still diagnosing whether your condensation is actually a seal failure, start with our guide to condensation between window panes before spending anything.
Confirm It Is Actually Seal Failure
Before spending money, rule out the two condensation types that require zero repair.
Run your finger across the fog. If you can wipe it off from the inside, that is surface condensation caused by high indoor humidity. Fix it with exhaust fans and a target of 30–35% relative humidity in winter.
If moisture appears on the outside of the glass on cool mornings and burns off by 10 a.m., that is exterior condensation proving your window insulates well. Neither situation involves a failed seal.
Seal failure condensation is trapped between the panes. You cannot touch it from either side. It often appears as a cloudy haze that shifts position over days but never fully clears.
On some windows, you will also notice a white mineral deposit that does not correspond to current moisture. That is permanent etching from long-term moisture exposure, and it will not come out even after repair.
Three Repair Options Compared
| Defogging | IGU Replacement | Full Window Replacement | |
|---|---|---|---|
| Cost | $75–$150/pane | $150–$400/pane | $300–$1,300/window |
| What it fixes | Visible fog only | Glass, seal, gas fill, desiccant | Everything (frame + glass) |
| What it doesn’t fix | Seal, gas fill, insulating value | Worn frame, weatherstripping | — |
| Longevity | 1–3 years | 10–20 years | 20+ years |
| Best for | Pre-sale cosmetics | Sound frames, 1–2 windows | 3+ failed windows or bad frames |
Defogging: Cosmetic Fix, Not a Repair
A defogging technician drills two small holes in the glass, flushes a cleaning solution through the cavity, vacuums out moisture, and plugs the holes with desiccant vents. The fog clears, sometimes immediately, sometimes over several weeks as residual moisture escapes through the vents.
What the clear glass hides: the argon gas that provided insulating value leaked out months or years before the fog appeared. Defogging does not replace that gas and does not repair the failed seal. Your window looks fixed but still performs like single-pane glass thermally.
The DOE notes that Low-E coatings reduce energy loss by 30–50%, but those coatings depend on a sealed gas fill to perform. Without argon between the panes, the coating is fighting heat transfer through bare air instead of an insulating gas layer.
Defogging makes financial sense in exactly one scenario: you are selling a home within 6–12 months and need clear glass for showings. At $75–$150 per pane versus $150–$400 for IGU replacement, the savings are real if longevity does not matter to you. As a long-term repair, it fails every time.
DIY Defogging Kits: Save Your Money
Kits sold online include a diamond drill bit and cleaning solution along with desiccant plugs. The pitch is simple: drill two holes, flush the cavity, then plug.
The reality from homeowner forums is less encouraging. The drill-and-flush approach clears fog temporarily, but moisture re-enters through the same broken seal — and the underlying issue, as glaziers point out in those threads, is that drilling does nothing for the failed perimeter seal itself.
Worse, drilling into tempered glass (required by code in bathrooms, near doors, and below 18 inches from the floor) will shatter it. And any drilling voids most manufacturer warranties, eliminating what might have been a free repair.
If you are tempted by a cheap kit to avoid a $200 IGU replacement, consider that the kit may buy you a short stretch of clarity at the cost of your warranty coverage.
IGU Replacement: The Actual Fix
IGU replacement removes the failed glass unit from the existing frame and installs a new one with fresh seals and a full argon gas fill. The desiccant strips inside the spacer bar get replaced too. Frame stays. Performance returns to factory spec.
The process works like this:
- A glass shop technician removes the interior stops (the trim pieces holding the glass in the frame)
- The old IGU lifts out of the frame channel
- The channel gets cleaned and inspected for frame damage, old glazing tape, and debris
- Measurements go to the fabricator: width, height, glass thickness, and specs for Low-E coating, gas fill, and spacer type
- The fabricator builds a custom IGU (1–2 week turnaround)
- The new unit gets set on glazing blocks, sealed with glazing tape, and the stops go back on
Installation takes 1–2 hours per window. Total cost runs $150–$400 per pane depending on size and glass type (tempered or specialty coatings push toward the high end). That is 50–70% less than full window replacement.
One critical check before ordering: press your thumbnail into the vinyl frame on a cool morning. Healthy vinyl flexes and springs back. If it dents permanently, feels brittle, or chalks white onto your finger, the frame is degrading. A new IGU in a dying frame will outlast its housing, so full replacement is the better investment.
Finding the Right Glass Shop
Not every glass company does IGU replacement. Many residential glass shops focus on shower doors and mirrors; you need one that fabricates or sources insulated glass units and has experience with residential window frames.
Ask whether they fabricate IGUs in-house or order from a supplier. In-house fabrication means faster turnaround and tighter quality control — shops that source out add 3–5 extra days and a middleman who may not know the product. Ask also whether they can match your existing Low-E coating and gas fill. A mismatch creates a visible color difference between the repaired pane and its neighbors; if the windows use a Cardinal or AGC coating, request the specific glass number so you can confirm the match.
Find out whether they measure on-site or need the sash brought in. On-site measurement is standard for large fixed units, but for operable windows some shops offer same-day service if the sash is dropped off by morning. Finally, ask about the warranty on the replacement IGU itself. Reputable shops back their glass for at least 5 years; no warranty on the seal means the fabrication quality is suspect.
Skip any company that suggests defogging as a “just as good” alternative to IGU replacement. That tells you where their expertise, or their profit margin, actually lies.
Filing a Warranty Claim for Seal Failure
Seal failure on a window within its warranty period should be a free repair. Most major brands (Andersen, Pella, Milgard, JELD-WEN) cover glass seals for around 20 years, though entry-level lines can run shorter.
Coverage varies in ways that matter at claim time. The five elements to check on your specific paperwork are duration, what counts as covered “failure” versus excluded breakage, transferability to a future owner, proration (some lines reduce payouts as the warranty ages), and exclusions for specialty glass or coastal salt-spray exposure. Pull the warranty document for your exact product line — terms differ between a builder-grade vinyl line and a manufacturer’s flagship.
File directly with the manufacturer, not your installer or dealer. Installers often discourage warranty claims because they handle the labor with little or no compensation once the early labor-coverage years lapse. The manufacturer’s warranty department is who approves the replacement glass. To file, you will need the purchase receipt or closing documents showing the window purchase date, the serial number from the spacer bar label (visible between the panes on most windows, near the bottom corner), and photos of the full window and close-up condensation. Some manufacturers also require proof of maintenance to process claims.
Expect a few weeks from submission to glass in hand: documentation goes in, the manufacturer sends an inspector or approves from photos, and they ship a replacement IGU. Some warranties cover installation labor for the early years of coverage; many do not. Budget a standard single-window service call to have a glazier install the warranty-provided glass if labor is not covered.
Second-owner trap: transferring a warranty to a second owner often requires registration within a short window after the home sale. Check your closing documents for warranty transfer paperwork and read the original warranty document for the exact deadline. Brands differ here — some let coverage follow the home automatically, others require active registration or restrict transferred coverage to a fraction of the original term.
When Repair Stops Making Sense
IGU replacement is smart for one or two isolated failures on windows under 15 years old with solid frames. The math changes fast when failures cluster.
At $150–$400 per IGU, replacing three panes costs $450–$1,200. That is approaching the cost of two or three full window replacements at $300–$1,300 each . Worse, the remaining original windows are on the same aging timeline.
Seal failure on vinyl windows accelerates after year 15. It is a sign of overall window aging , not isolated bad luck.
The practical threshold: when three or more windows show seal failure on the same house, full replacement beats chasing IGU failures one by one. You get new frames with fresh weatherstripping and hardware, plus a 20-year warranty covering everything. Our window cost overview breaks down pricing by project scope; bulk replacement typically saves 10–15% over piecemeal work.
Before replacing, check what glass type options are available for your replacement IGUs or new windows. Upgrading from standard Low-E to a solar-control coating like Cardinal LoE3-366 can cut cooling loads significantly, especially on south- and west-facing windows where vinyl windows age fastest .