Foggy Double-Glazed Window: Repair or Replace?
A foggy double-glazed window means the sealed unit has failed: moisture has got in between the 2 panes and condensation is trapped where you cannot wipe it. It cannot be resealed or de-fogged back to as-new; the correct fix is to replace the sealed glass unit, not repair the seal. The frame usually stays, and only the insulated glass unit inside it is swapped. Fogging almost always signals the unit has lost its argon fill and its insulating value too. Glazing Adelaide connects you with vetted local glaziers so you can compare 3 free quotes on a replacement sealed unit.
Key takeaways
- Fog between the panes means the sealed unit has failed, not dirty glass.
- The seal cannot be reliably repaired: the glass unit is replaced.
- The frame typically stays; only the insulated glass unit is swapped.
- A failed unit has usually lost its argon fill and insulating value.
- Compare 3 free quotes on a replacement sealed unit, not a "de-fog" service.
Why double-glazed windows fog up
A double-glazed unit is 2 panes of glass sealed around the edge with a spacer and a drying agent, with an insulating gas (usually argon) or dry air in the gap between them. That sealed gap is what gives double glazing its insulation. When the edge seal fails, outside air and moisture leak into the gap, and once warm humid air meets the cooler inner pane you get condensation trapped between the panes: the fog you cannot wipe away.
Seals fail with age, from constant expansion and contraction as temperatures swing (Adelaide summers are hard on them), from water sitting in the frame, or from a manufacturing fault. Once it goes, it does not un-fail. The fog will come and go with the weather, sometimes clearing on a dry day and returning on a humid one, but the unit is compromised for good.
Why you replace the unit, not the seal
You will see "de-fogging" services advertised that drill the unit, dry it out and reseal it. Be cautious. Even where the fog clears, that process does not restore the argon fill or the original edge seal, so you are left with a window that looks better but has lost most of its insulating performance and will often fog again. It treats the symptom, not the failure.
The proper fix is to replace the insulated glass unit (the sealed double-pane sandwich) with a new one. In most cases the existing frame and sash stay in place, and only the glass unit inside is measured and swapped. That restores both the clear view and the insulation. It costs more than a de-fog gimmick, but it is the repair that actually holds.
What replacement involves and costs
A glazier measures the exact unit size, the glass thickness and the gap width, and orders a matching sealed unit made to those dimensions. Because it is made to order, there is usually a lead time of a week or 2, and the price varies with the unit size, the glass type (low-e coatings and toughened glass cost more) and how many windows have fogged, since seal failure often shows up across several units of the same age.
If only 1 window has fogged, replacing that single unit is straightforward. If several have gone at once, it is worth quoting them together. Either way, get the frame checked while the glazier is there, because water sitting in a frame can be what killed the seal in the first place.
Glazing Adelaide connects you with vetted, licensed local glaziers who replace sealed units correctly, so you can compare 3 free quotes rather than paying for a de-fog that will not last.
Ready to get real numbers? Compare 3 free quotes from vetted Adelaide specialists for glass repair.
Frequently asked questions
Not reliably. De-fogging services may clear the condensation, but they do not restore the argon fill or the seal, so insulation stays lost and fog often returns. Replacing the sealed unit is the proper fix.
Usually not. In most cases only the insulated glass unit is replaced and the existing frame and sash stay, unless the frame itself is damaged or rotten.
Units installed together age together, so when one seal fails the others of the same batch are often close behind. It is worth having them all checked and quoted at once.