Misted double glazing
Misted double glazing replacement
Foggy glass you cannot wipe away means the sealed unit has failed. Often the fix is just new glass in a sound frame — not a whole new window.
Misting is the classic sign of a failed sealed unit. If you can see condensation or a milky haze between the two panes — and no amount of wiping clears it — the airtight seal around the edge of the glass has broken down. Moisture has worked its way into the cavity, and the insulating gas that used to fill it has escaped. The window still functions, but it looks tired and no longer keeps the heat in the way it should.
Why sealed units mist up
A double-glazed unit is two panes bonded to a spacer bar, with a desiccant to absorb stray moisture and a perimeter seal to keep everything airtight. Over years of heating and cooling, that seal expands and contracts until it eventually fails — usually after a decade or more, though poor original manufacture, standing water on the sill or south-facing heat can bring it on sooner. Once the seal goes, the desiccant saturates and the tell-tale mist appears.
Importantly, misting is a glass fault, not a frame fault. If your frames are sound, you almost certainly do not need a whole new window — just a replacement sealed unit. Our guide on replace the glass or the whole window? walks through how to tell the difference.
How failed units are replaced
Replacing a misted unit is a tidy job. The fitter removes the glazing beads, lifts out the failed unit and measures the aperture precisely, then a new made-to-size sealed unit is installed and re-beaded. The frame, hinges and locks stay exactly as they are. Many homeowners take the chance to upgrade the new glass — a higher energy rating, acoustic glass for a noisy road, or obscure glass for a bathroom — for a small difference in cost. If you are deciding whether it is worth mending at all, this guide on repair or replace — how to decide is a good reference.
When a whole new window is the better call
If several units across the house have misted, the frames are the same age and starting to look tired, or you have been meaning to upgrade to slimmer, warmer windows anyway, replacing the windows may make more sense than chasing failed units one at a time. Our quotes by window type hub explains how each style is priced, and full-house window replacement covers a wider project.
Getting a misted-unit quote
Replacement units are priced by size and glass specification, so treat any single figure as a guide until a surveyor has measured. You can get a fast quote direct, no showroom, or browse the current double glazing deals and prices for context. Funding and contribution options may be available subject to eligibility and a home survey, and £0-upfront options may be available for those who qualify. The quote and home assessment are free and no-obligation.
Get a misted-unit replacement quote
Tell us how many units have fogged and your postcode and we will match you with vetted installers for a free, no-obligation assessment.