Misted Double Glazing
Fog between the panes means the sealed unit has failed — the glass can usually be swapped without touching the frame.
Most people landing here want one thing: to work out whether a foggy sealed unit can be swapped on its own or whether the whole window is finished. That's what this page answers — no scare tactics, no automatic upsell to a full replacement.
What you'll notice first
- a permanent haze or milky film between the two panes that a cloth can't reach
- water droplets or tide-marks sitting inside the cavity after cold nights
- a rainbow-ish smear across the glass in low winter sun
- one pane feeling noticeably colder to the palm than the same pane next door
What actually causes it
- 1the perimeter edge seal has perished, letting moist air into the cavity
- 2the desiccant in the spacer bar has saturated and can no longer absorb the moisture
- 3units bedded without drainage so rainwater sits against the seal in the rebate
- 4south-facing glass going through daily heat cycles that pump the seal open over years
Your realistic options
The frame, hinges and handles stay. We template the failed unit, order the glass to size and swap it in about 20 minutes per opening once the glass arrives.
If the frame is sound it's a sensible moment to move to a warm-edge spacer, argon fill and a low-E soft coat, so the replacement performs better than the original ever did.
Only worth it if the frame is also failing — welded corners opening, sashes dropped, or the profile so old that matching glazing beads no longer exist.
Misting on its own is a glass problem, not a window problem. If the frame closes cleanly, locks properly and the gaskets are still supple, replacing the sealed unit is the honest answer and we'll say so. Replacement of the whole window only stacks up when several openings have failed at once and the frames are into their third decade.
What we check on survey
- we check whether the bead is internal or external, because external beading changes the fitting method
- we note the spacer depth so the replacement unit sits at the right thickness in the rebate
- we look for standing water in the drainage slots, the usual reason a unit failed early
- we test the hinges and locks while we're there so you know whether the frame has life left
How it's priced
Cost tracks glass area, whether the unit is toughened (needed near doors and low-level glazing), and whether it's obscure or leaded. Small landing windows sit at the bottom of the range, a wide bay unit with toughened safety glass at the top. We measure and quote per opening rather than a blanket price.
How urgent is it? Not an emergency. A misted unit is ugly and slightly less efficient, but it isn't a security or water-ingress risk — most people live with it until they're ready to do several in one visit.
Stopping it coming back
- keep the drainage slots along the bottom of the frame clear of paint and cobwebs
- don't wedge the sash open against a strong wind — it strains the corner welds and the seal
- wipe down condensation on the inside face in winter rather than letting it pool on the bead
Misted Double Glazing — questions we get asked
Can misted double glazing be fixed without replacing the glass?
No. The drilling-and-drying services you'll see advertised remove the visible fog for a while but the cavity is no longer sealed, so it comes back and the unit loses its gas fill permanently. Replacing the sealed unit is the only durable fix.
Do you have to take the whole window out?
No. The glazing beads come off, the failed unit lifts out, the new one goes in on packers and the beads clip back. The frame never leaves the wall.
How long does the replacement glass take to arrive?
Standard clear toughened units are usually the quickest; obscure patterns, leaded designs and anything oversized take longer because they're made to order. We give you the lead time in writing with the quote.
Is a misted unit still under guarantee?
If the original installer is still trading and the unit is inside its guarantee period, claim from them first — we'll tell you honestly if that looks like the better route.
If replacement is the answer
Misted Double Glazing in your town
Other faults worth ruling out
Most break-ins through glazed openings exploit the cylinder or the keeps, both of which are upgradeable in an afternoon.
ReadFrench doors are a pair, so the fault is usually in how the two leaves meet rather than in either leaf on its own.
ReadYellowing is cosmetic and treatable; splits at the welded corners are structural and aren't.
ReadLet's make your house feel more like home.
Fill in a few details and we'll come back within 24 hours with a clear quote — no callout fee, no pressure.