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Professional Defogging or IGU Replacement for Failed Seals?
I’m comparing professional defogging with replacing the insulated-glass unit, not the whole window. The moisture is trapped between the panes, so it looks like the sealed unit has failed.
I’m trying to weigh a few things:
- How many panes are affected and roughly how large they are
- Whether the frame, sash, locks, and hinges are still in good shape
- Whether the fogging is occasional or constant
- Whether there are mineral deposits, etching, or low-E coating damage
- Any remaining warranty and the window’s expected service life
Defogging seems less disruptive. From what I understand, it involves small openings to dry or treat the space between the panes, then vents or plugs are installed. My concern is whether it works well when there are heavy deposits, and whether haze tends to come back. I’d also want to know exactly what appearance guarantee is included.
Replacing just the IGU costs more upfront, but it restores the sealed cavity. It seems like the better option if the coating or glass is damaged and the rest of the window still has plenty of life left. I’d check the manufacturer warranty before paying for either option too, since a failed seal might be covered even if installation labor is not.
If you’ve compared the two, what made you choose defogging or IGU replacement? Did the condition of the frame and hardware affect the decision, and how has the glass looked after a few seasons?
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5 replies
I’d be cautious about treating defogging as an appearance fix. Drying the cavity may stop the active fogging, but it can’t necessarily remove mineral deposits, and etched glass or damaged low-E coating won’t be restored by adding vents or plugs. In that situation the window may stay permanently hazy even though the moisture is gone.
For a window where visual clarity matters, replacing the IGU is usually the more predictable choice, assuming the frame and sash are sound. Defogging makes more sense when the remaining haze is acceptable and the main goal is reducing condensation at lower cost. I’d ask the defogging company for photos of comparable jobs and a written guarantee covering residual haze, not just whether moisture returns.
The point about a written guarantee covering residual haze seems especially important. Before comparing prices, could a contractor measure the existing IGU and confirm the glass specifications? Thickness, spacer type, overall unit dimensions, and the low-E coating’s orientation can all affect whether the replacement fits the sash and performs as intended. A quote based only on rough width and height might miss those details.
I’d want the quote to state whether those measurements are being verified on site, and whether the replacement glass will match the original thermal and appearance characteristics.
When the contractor confirms the IGU specifications, I’d also have them separate the warranty terms for the glass, seal failure, and labor. A “20-year glass warranty” may cover replacement of the sealed unit but not the cost of removing the sash, installing the new unit, or returning to fix a failed seal later.
The quote should state who handles a warranty claim, whether labor is included, and whether the warranty is transferable. It’s also worth checking whether installation by that particular contractor is required to preserve coverage. A slightly cheaper IGU can become less attractive if the future labor is entirely out of pocket.
The labor warranty may still leave a gap around removal. I’d have the quote identify who’s responsible for disposing of the failed IGU and for repairing any sash, stops, seals, or glazing damage found once the unit is removed. Those costs may fall outside both the glass warranty and the installer’s standard labor coverage.
It’s also worth stating whether the contractor will stop and obtain approval if removal reveals a damaged or deteriorated sash. Otherwise, an apparently fixed-price replacement can turn into an unexpected repair charge, especially on older windows.
- Jackr11’s point about hidden sash damage is important. The quote should also state how the contractor will protect the open window if an approved repair is needed, such as temporary weatherproof covering or securing the sash overnight.
- It should specify whether the IGU installation is rescheduled without another trip or mobilization charge after the repair.
- Also clarify whether the contractor will remove and reinstall stops or glazing materials without damage, and who pays if those components need replacement.