Repairs and maintenance

Misted and blown glass units

A misted or blown glass unit is a sealed double-glazed unit whose edge seal has failed, letting moist air into the cavity between the panes. The fix is a new made-to-measure sealed unit, fitted into the existing frame, rather than new windows or a new shopfront.

Book a repair visit Call 0800 088 6341

Misted double-glazed shop window with a failed seal

How do you know you need this?

You need a new unit if there is condensation or a milky haze between the two panes that you cannot wipe away from either side. Water marks, streaks or drips inside the cavity are the same fault at a later stage. Condensation on the room-facing surface is different: that is usually a ventilation or humidity issue in the shop, and a new unit will not cure it.

What do we fix?

Misted fixed windowThe old unit comes out and a new one of the same thickness goes into the existing frame.

Door and side panel unitsThese sit in critical locations, so the replacement is built with the right safety glass on each side.

Water in the cavityVisible water means the seal failed some time ago. We check how it got in before fitting the new unit.

Blocked frame drainageWater sitting in the glazing pocket attacks the edge seal. Clearing the drainage path helps the new unit last.

Better glass in the same frameA replacement unit can often include solar control or low-emissivity glass at the same overall thickness.

How much does it cost to replace a misted glass unit?

A replacement sealed unit costs £165 to £695 ex VAT per sealed unit. Size, toughened or laminated panes and access set the price, and the frame normally stays. Send the rough size and a photo of any marks on the spacer bar. If the unit cannot be priced that way, a charged diagnostic visit, from £125 ex VAT, is needed, and we give you that figure first.

Guide prices exclude VAT. Your repair price, including any visit charge, is confirmed before work starts.

What is the specification?

Sealed unit standard	BS EN 1279
Build-up	Two panes, spacer bar, desiccant and a sealed cavity of dry air or argon
Overall thickness	Commonly 24 mm or 28 mm, measured on site before ordering
Safety glass	Toughened BS EN 12150 or laminated BS EN 14449 where the position requires it
Warranty	Manufacturers' warranties cover glass units; our 10-year guarantee covers workmanship

How does the job run?

Confirm the fault
Check that the mist sits between the panes and will not wipe off either face.
Measure the unit
We confirm the size, thickness, glass type and spacer, and note any safety glass markings.
Order the new unit
The sealed unit is made to measure, and the old one stays in until it arrives.
Swap the unit
Beads and the old unit come out, drainage is cleared, and the new unit is packed and sealed in.

Common questions

Can misted double glazing be repaired?

No lasting repair exists once the edge seal has failed, so the unit is replaced. Drilling and drying services may clear the view for a while, but they do not restore the seal or the gas fill. Changing only the unit keeps your frame.

Is a misted unit still insulating?

A misted unit usually insulates less well, because gas has escaped and damp air has replaced it. The glass is still a barrier, so it is rarely an emergency. It does look poor, and moisture can leave permanent marks on the inner faces.

Could a misted unit still be under warranty?

It could be, if the unit is recent. Manufacturers' warranties cover glass units, so look for a maker's name or date on the spacer bar and check your paperwork. Our 10-year guarantee covers workmanship only, and applies to work we have carried out.

How long does a replacement sealed unit take?

Sealed units are made to measure, so the wait is typically counted in weeks rather than days, depending on size and glass type. You get the expected lead time alongside your price, and the old unit stays in place until the new one is ready to fit.

Will a new unit match the others in my shopfront?

Usually, if we match the glass type, coatings and spacer colour. A new unit can look slightly different beside old panes, particularly if those have a tint. We check this before ordering, and can replace adjoining units together if you prefer.

Which materials go with this?

Book a repair visit

Tell us what has gone wrong. Send photos when we reply and we can often price it without a visit.

What do you need?

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