Glass & repairs
Misted Double Glazing Repair
Misted double glazing repair means replacing a sealed unit whose edge seal has failed, letting moist air into the gap between the panes. It is needed when fog, droplets or white staining appear inside the unit and cannot be wiped away from either side of the glass.
- Guide from £155
- Free survey
- Written quote
- UK-wide
- Free survey for new glazingMeasured on site before anything is made
- Written quoteThe price is fixed for the specification shown
- Every glazing jobGlass, windows, doors and commercial
- UK-wide coverEngland, Wales, Scotland and Northern Ireland
- Guarantee terms in writingSet out with every quote
How our misted glass repair service works
We replace misted or blown sealed units in existing uPVC, aluminium, timber and composite windows and doors, so the frames stay in place. A glazier surveys each window to confirm the mist is between the panes rather than on the surface, checks the frame and drainage, and measures the unit. You then get a written quote that fixes the price for the specification shown. The new units are made to order. On the fitting visit, our glaziers remove each failed unit, clean the rebate, set the new unit on packers and refit the beads. Old units are taken away. You can upgrade to low-E, obscure or safety glass at the same time.
What's included
- Survey to confirm the mist is inside the unit
- Measurement of each failed sealed unit
- Written quote fixing the price for the specification
- Made-to-measure replacement units matching your windows
- Removal of old units and cleaning of rebates
- Fitting on packers with drainage slots checked
When you might need misted glass repair
- Fog or droplets appear between the panes and cannot be wiped
- White streaks or staining have formed inside the sealed unit
- Mist inside the glass comes and goes with the weather
- A window looks permanently cloudy even after cleaning both sides
- Several units of the same age are starting to mist
Guide prices
| Typical job | Guide price inc VAT |
|---|---|
| One misted unit, 600 × 900 mm | £155 – £195 |
| Two misted units, 600 × 900 mm | £305 – £395 |
| Four misted units, 600 × 1100 mm | £685 – £875 |
| Misted unit in a door, toughened | £305 – £385 |
Options to choose between
Like-for-like clear unit
A direct replacement matching the thickness and look of the original unit, for windows where no change in performance is needed.
Low-E upgrade unit
A coated pane and gas-filled cavity that reduce heat loss compared with older plain glass units, fitted in the same frame.
Obscure glass unit
Patterned glass for bathrooms, landings and front doors, chosen to match existing obscure panes or to add privacy.
Toughened safety unit
Both panes toughened, for misted units in doors, beside doors or low down where safety glass is required.
Laminated safety unit
A unit with laminated glass that holds together if broken, useful for ground-floor security and safety in critical locations.
Georgian bar or leaded
Decorative bars or lead designs remade to match the originals so the new unit lines up with neighbouring windows.
Good to know about misted glass repair
A sealed unit has a spacer bar around its edge filled with desiccant, a drying agent that absorbs any moisture inside the cavity. When the edge seal fails, damp air keeps getting in until the desiccant is saturated, and condensation then forms between the panes where it cannot be wiped off.
Condensation on the room-side surface of the glass is not the same problem. It usually comes from humid indoor air meeting a cold pane and can be wiped away. Only mist trapped between the two panes means the sealed unit itself has failed and needs replacing.
Early seal failure often shows only on cold mornings or after rain and clears during the day. As the desiccant fills, the mist lasts longer and white mineral staining can form on the inner faces. Staining inside the unit cannot be removed by cleaning from either side.
Common causes of seal failure include water sitting in the frame rebate because drainage holes are blocked, units fitted without correct packers, strong sun on dark frames, and age. Clearing the drainage slots in the frame helps protect the new unit from the same problem.
Some services offer to drill the glass, flush the cavity and add a vent instead of replacing the unit. This can improve the look, but it does not restore the original seal, and any gas fill that helped the unit insulate has already been lost. Replacement restores a sealed cavity.
Once the seal has failed, any argon or other insulating gas in the cavity has escaped and been replaced by ordinary damp air. The unit insulates less well than when it was new, and moisture inside can gradually leave deposits that dull the glass.
A new unit has to match the overall thickness of the old one so it sits in the existing rebate and takes the original beads. The glazier also notes any Georgian bars, leaded designs or obscure patterns so the replacement matches the other windows in the room.
If the misted unit is in a door, beside a door or low down near the floor, the replacement should be safety glass. In England, Approved Document K sets out these critical locations, and the replacement unit should meet them even if the original glass did not.
Replacing a misted unit is usually a short job per window once the new unit has been made. The old unit is lifted out, the frame rebate and drainage cleaned, and the new unit set on packers so the weight is supported and any opening sash stays square.
The price of replacing misted units depends on the size of each unit, the glass specification, any bars or decorative features, how many units are done together, and access. Several units on one visit usually cost less each than separate visits for single windows.
A misted unit is a good opportunity to upgrade an older plain glass unit to one with a low-emissivity coating and gas fill. The new unit reduces heat loss through the glass and keeps the room-side pane warmer, without any change to the frame.
Check the paperwork for your windows before booking. Many sealed units come with a manufacturer guarantee against misting, and if your windows are still covered, the original installer or manufacturer may be responsible for replacing the failed unit under its terms.
Rules and regulations
Building regulations differ between the four UK nations. Here is what usually applies to misted glass repair; your written quote confirms the detail for your property.
England
Approved Document K requires safety glass in critical locations in England: glazing in doors and in side panels within 300 mm of a door, up to 1500 mm above floor level, and any glazing in walls or partitions up to 800 mm above floor level.
Approved Document L sets the minimum energy performance for replacement windows and doors in existing homes in England: a U-value of 1.4 W/m²K, or Window Energy Rating band B for windows; doors can instead meet a Door Set Energy Rating (band B, or band C for doors more than 60% glazed); rooflights need 2.2 W/m²K.
Wales
In Wales, Approved Document N covers safety glazing: safety glass is needed in and around doors and in low-level glazing where people could walk into it.
Wales sets its own energy standards in the Welsh Approved Document L. Replacement windows, doors and rooflights must meet the limiting values set there, which your quote will reference.
Scotland
Section 4 (Safety) of the Scottish Technical Handbooks covers glazing that people could collide with, such as glass in and beside doors and low-level glazing, where safety glass is needed.
Section 6 (Energy) of the Scottish Technical Handbooks sets the thermal performance that replacement windows, doors and rooflights should achieve.
Northern Ireland
Technical Booklet V covers safety glazing in Northern Ireland, including glass in and around doors and low-level glazing where people could walk into it.
Technical Booklet F1 sets the energy performance that replacement windows, doors and rooflights need to meet in Northern Ireland.
What happens next
Tell us about the job
Use the quote form, call, WhatsApp or live chat. Photos and rough sizes help.
Survey and measure
A glazier visits, checks the opening and measures. For simple glass swaps this is often done on the same visit as fitting.
Written quote
You get a written quote with the specification, price and guarantee terms. Nothing is ordered until you agree.
Made and fitted
Glass, frames or panels are made to size and fitted. We tidy up and take the old glass away.
Misted Glass Repair questions
Why has condensation appeared between my double glazing panes?
Condensation between the panes means the edge seal of the sealed unit has failed. Damp air has got into the cavity, and the drying agent in the spacer bar can no longer absorb it. The cause is often age, water sitting in the frame, poor packing or strong sun on the frame. The fix is to replace the sealed unit.
Can misted double glazing be fixed without replacing the window?
Yes. In most cases only the sealed unit needs replacing, not the frame. The glazier removes the beads, lifts out the misted unit and fits a new one made to the same thickness. Your frames, hinges, handles and locks stay as they are, provided they are in good condition, which the glazier checks at the survey.
How much does it cost to replace a misted sealed unit?
The cost depends on the size of the unit, the glass type, any Georgian bars, leaded or obscure features, how many units are done together, and access to the window. Larger units, safety glass and upper-floor windows cost more. See the guide prices for typical sizes, then get a written quote for your exact windows.
Is it worth replacing misted units or should I get new windows?
If the frames are sound, square and the hinges and locks work, replacing only the misted units is usually the more economical option. New windows make more sense if the frames are rotten, warped, draughty or hard to open. The glazier checks the frames at the survey and the quote will say if replacing units is not good value.
Does misted double glazing lose heat?
A misted unit usually insulates less well than when it was new, because any insulating gas in the cavity has escaped and been replaced with damp air. The mist itself also reduces clarity. Replacing the unit restores a sealed cavity, and choosing a low-E unit can improve on the original performance where the old unit was plain glass.
Can you clean the inside of a misted double glazing unit?
Not without breaking the seal. Some firms drill the glass, flush the cavity and fit a small vent, which can clear the mist for a while. It does not restore an airtight seal or gas fill, and white staining may not fully clear. Replacing the unit is the reliable way to restore a clear, sealed cavity.
How long does it take to replace a misted unit?
There are usually two visits. The first is a survey to measure each unit. The second is fitting, once the new units have been made to order. Fitting usually takes a short time per window, with little mess. Your quote sets out when the units are expected, and we will tell you honestly when a glazier can attend.
Are misted units covered by a guarantee?
Often they are, for a period after installation. Many sealed unit manufacturers guarantee against misting, and the terms are set out in the paperwork from the original installer. If your units are still covered, contact that installer first. Units we supply carry manufacturer guarantees, and the terms are confirmed in writing with your quote.
Will a new unit match my other windows?
It can. The glazier records the unit thickness, spacer bar colour, any Georgian bars or leaded designs, and the obscure glass pattern if there is one. Most details can be matched closely. If an obscure pattern has been discontinued, the quote offers the closest available alternative so you can decide before anything is ordered.
How can I stop new sealed units misting early?
Keep the drainage slots at the bottom of the frame clear, so rainwater does not sit around the unit edges. Avoid pressure washing the seals, and do not paint over glazing gaskets. Check that opening sashes close properly, as a dropped sash can stress the unit. Report any cracked beads or failed gaskets early.
Misted Glass Repair near you
Choose your county or area for local details, towns we cover and the rules that apply where you live.
England
- Bedfordshire
- Berkshire
- Bristol
- Buckinghamshire
- Cambridgeshire
- Cheshire
- Cornwall
- County Durham
- Cumbria
- Derbyshire
- Devon
- Dorset
- East Riding of Yorkshire
- East Sussex
- Essex
- Gloucestershire
- Greater London
- Greater Manchester
- Hampshire
- Herefordshire
- Hertfordshire
- Isle of Wight
- Kent
- Lancashire
- Leicestershire
- Lincolnshire
- Merseyside
- Norfolk
- North Yorkshire
- Northamptonshire
- Northumberland
- Nottinghamshire
- Oxfordshire
- Rutland
- Shropshire
- Somerset
- South Yorkshire
- Staffordshire
- Suffolk
- Surrey
- Tyne and Wear
- Warwickshire
- West Midlands
- West Sussex
- West Yorkshire
- Wiltshire
- Worcestershire
Scotland
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