My double glazing has gone foggy inside — can just the glass unit be replaced, or the whole window?
Several of my windows have gone foggy between the panes — a permanent misting/condensation I can't clean because it's *inside* the sealed glass. From reading here I gather the edge seal has failed and it can't be "dried out."
What I want to avoid is being sold whole new windows if I don't need them. So:
- Can just the sealed glass unit be replaced while keeping the existing aluminium frame?
- If so, what actually drives the cost — glass size, the type (double-glazed / low-E / toughened), access/height, number of units?
- Is there any case where you *do* have to replace the whole window?
Got maybe five affected windows of different sizes, one of them large and high up. Trying to understand whether this is a glass-swap job or a window-replacement job before I get quotes.
3 answers
Short answer: in almost all cases you replace only the failed sealed glass unit and keep the aluminium frame — the frame is fine, it's the glass unit's edge seal that's gone. Replacing whole windows for foggy glass is usually unnecessary. Cost is driven mainly by the glass size, the spec, and access.
Why it's a glass-swap, not a window job: a double-glazed unit is two panes bonded to a spacer and sealed at the edge; when that seal fails, moisture gets between the panes and mists — but the frame, hinges and hardware are untouched. A glazier measures the unit, orders a matching sealed unit, and swaps it into the existing frame. Same glass thickness and spec for a clean fit.
What drives the cost (roughly in order): 1. Glass size — bigger units cost more (glass is priced by area). 2. Spec — plain double-glazed vs low-E (heat-reject) vs toughened (required for large panes, doors, low-level glass) each step up in price. 3. Access — your large, high-up one is the pricier job: it may need more people, ladders/access equipment, which is a real line item. 4. Quantity — doing five at once usually gets a better per-unit rate than one.
When you'd replace the whole window: only if the frame itself is corroded, warped or the hardware is failing too — otherwise it's glass only.
Get an aluminium and glass specialist to measure all five (especially matching the spec of the big one) and quote glass-only. If a quote is for whole new windows on foggy glass alone, get a second opinion. Anyone done a batch of sealed-unit swaps — was the high/large one much more than the small ones?
Had two foggy units swapped in an apartment and it was exactly as described — glass only, frames kept, done in a morning. The quote that tried to sell me new windows was more than double the one that just replaced the glass units. So definitely get more than one quote and specifically ask for "replace the sealed unit, keep the frame." The difference in price for the same end result (clear windows) was huge.
Worth considering the upgrade angle while you're at it: since you're paying for new sealed units anyway, ask what a low-E (heat-reflective) unit costs versus plain double-glazed for the sun-facing ones. The labour to swap is the same; the only delta is the glass spec, so it can be a cheap moment to cut heat gain on the west/south windows. Wouldn't bother on shaded ones. Doing all five at once got me a better rate too.
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