The cost of replacing a double glazed sealed unit depends mainly on its size, the glass specified, whether safety glass is required, how easy the window is to reach and how many units are done in one visit. Replacing only the unit usually costs less than a complete window because the frame stays in place. See the guide price table on this page for typical ranges.
What does the price of a replacement sealed unit cover?
A sealed unit price normally covers a survey to measure the existing unit, a new unit made to those exact sizes, removal of the old unit, fitting of the new one on correctly placed packers, re-beading and disposal of the old glass. Check that the quote states each of these, because some prices cover the glass alone and leave fitting or disposal as extras.
Because every unit is made to order, the price is tied to a specification: overall thickness, glass type for each pane, spacer, any gas fill and any decorative features. A good written quote lists that specification for every unit so you can compare like with like. See the guide price table on this page for typical ranges, and use the factors below to understand why your quote may sit higher or lower.
How does the size of the unit affect the cost?
Size is the starting point. Larger units use more glass, need heavier handling and may need two glaziers to lift safely, so the price rises with area. Very large panes, such as those in patio doors, fixed picture windows or shopfronts, can also need specialist lifting equipment or extra people on site.
Small units are not always proportionally cheaper. Each unit has fixed costs for measuring, manufacture, delivery and fitting, so a very small pane still carries much of the same overhead as a mid-sized one. That is why the cost per square metre is usually higher for small units than for large ones.
Guide prices
| Typical job | Guide price inc VAT |
|---|---|
| Small double glazed unit, 500 × 700 mm | £135 – £175 |
| Standard unit, 600 × 900 mm | £165 – £205 |
| Large unit, 1200 × 1200 mm | £285 – £365 |
| Toughened unit for a door, 750 × 1800 mm | £345 – £435 |
| Triple glazed unit, 600 × 900 mm | £235 – £305 |
Which glass types cost more?
Standard double glazing uses two panes of annealed float glass, often with a low-emissivity coating on one pane to cut heat loss. Upgrading either pane changes the price. Toughened glass is heat treated after cutting and must be ordered to exact size, and laminated glass bonds two layers with an interlayer. Both cost more than annealed glass, but one of them is required wherever safety glazing is needed.
Other options add cost in the same way. Obscure patterned glass for privacy, acoustic laminate for noise, solar control coatings for sun-facing rooms, thicker glass for larger panes and self-cleaning coatings all change the specification. Triple glazed units use a third pane and a second cavity, so they cost more than double glazed units of the same size.
- Toughened safety glass in doors, side panels and low-level glazing
- Laminated glass for safety, security or noise reduction
- Obscure patterned glass for bathrooms and front doors
- Low-emissivity and solar control coatings
- Thicker glass for large panes
- Triple glazed units
| Factor | Why it affects the price | What to ask |
|---|---|---|
| Size | More glass and heavier handling for large units; fixed costs weigh more on small ones | Is the price per unit or per square metre? |
| Glass type | Toughened, laminated, obscure, acoustic and coated glass cost more than standard float | Which glass is specified for each pane? |
| Safety glass | Required in critical locations such as doors and low-level panes | Which units need safety glass, and how is it marked? |
| Decorative features | Georgian bars, leaded designs and shaped units take longer to make | Will the new unit match the existing pattern? |
| Access | Upper floors and roofs may need towers, platforms or scaffolding | Is any access equipment included? |
| Frame type | Putty-glazed, externally beaded or bonded units take longer to change | How is the old unit removed? |
| Quantity | Survey and visit costs are shared across more units | Is there a price for several units together? |
When is safety glass required, and how does it change the price?
Safety glass is required in critical locations, where people are most likely to walk into or fall against the glass. In England, Approved Document K sets out these locations, and its reference heights are 800mm and 1500mm above floor level and 300mm from the edge of a door. In practice that covers glazing in doors, side panels next to doors and low-level panes in windows.
Wales, Scotland and Northern Ireland each have their own guidance on safety glazing, and the Welsh and Scottish guidance describes similar zones. If the old unit in one of these locations was ordinary annealed glass, the replacement should be toughened or laminated. That is a common reason a quote is higher than expected, and it is a cost worth paying.
Why do decorative features and shapes add cost?
Units with Georgian bars between the panes, leaded designs, bevelled or etched glass, or stained-glass effects take longer to make and must be matched carefully to the existing windows. Shaped units, such as arched tops, circles or raked triangles, need a template and specialist cutting, so they are priced individually rather than by area alone.
Matching older units can also affect cost. Some obscure patterns and spacer colours are no longer manufactured, so the nearest current option may need to be agreed before ordering. The written quote should say exactly what will be supplied for each unit.
How do access and the frame type affect the price?
A ground-floor window that can be reached from inside is the simplest job. Upper-floor units, roof glazing, conservatory roofs and windows over conservatories, extensions or steep ground may need ladders with extra safety measures, a tower scaffold, a mobile platform or scaffolding, and that equipment adds to the cost.
The frame matters as well. Most uPVC and aluminium windows have beads that unclip, so the unit can be changed without disturbing the frame. Some older timber windows are glazed with putty or sealant, and some systems are glazed from the outside, which can take longer. Units in bifold or sliding doors, or bonded into frames, can also take more time to remove safely.
Is it cheaper to replace several units at once?
Often, yes. Much of the cost of a single unit is the survey, travel, set-up and fitting visit, so adding more units to the same visit spreads those fixed costs. If one unit has misted and others in the same house are of a similar age, it can be worth asking for a price for those as well while the glazier is surveying.
There is no obligation to do everything at once. Our glaziers can quote per unit so you can choose which to replace now and which to monitor. The written quote fixes the price for the specification shown, and guarantee terms are set out in writing with your quote.
How should you compare sealed unit quotes?
Compare specifications, not just totals. A lower price may be for a thinner unit, a basic spacer, no low-emissivity coating or annealed glass in a location that needs safety glass. Ask each installer to list, for every unit, the overall thickness, glass type for each pane, spacer type and any gas fill or coatings.
Check what happens on the day as well: whether removal and disposal are included, whether any access equipment is priced, and what happens if a frame turns out to be damaged when the old unit is taken out. Ask how the safety glass will be marked, so you can see that toughened or laminated glass has been fitted where it is needed.
- Unit size, overall thickness and glass type for each pane
- Safety glass where it is required, and how it is marked
- Spacer type and any gas fill or coatings
- Removal, disposal and access equipment
- Guarantee terms in writing
Frequently asked questions
Is replacing the sealed unit cheaper than replacing the whole window?
Usually, yes. Replacing only the unit keeps the frame, hinges and locks in place and avoids removing the old frame and making good the surrounding wall, so there is less material and labour. It only makes sense if the frame is sound. If the frame is rotten, warped or failing, a new window is usually the better use of money.
Can I get a price without a survey?
A guide price can be given from approximate sizes, photos and a description of the glass, and the guide price table on this page shows typical ranges. Because units are made to exact sizes, a glazier needs to measure on site before ordering. The written quote after the survey fixes the price for the specification shown.
Why is a toughened unit more expensive than a standard one?
Toughened glass is cut to its final size and edge-worked before being heated and then cooled with jets of air to strengthen it, and it cannot be cut afterwards. That extra process adds to the material cost. Where glass is in a critical location, such as a door or low-level pane, toughened or laminated safety glass is the right specification despite the higher price.
How long does it take to replace a sealed unit?
There are two stages. The unit is measured and then made to order, so there is a wait between survey and fitting that depends on the manufacturer and the specification. The fitting itself is usually a short job for a standard unit, measured in hours rather than days. Large, shaped or high-level units can take longer.
Do I need to replace all the misted units at the same time?
No. Each unit can be replaced on its own. Doing several in one visit can be more economical because survey and set-up costs are shared, so it is worth asking for prices for other units of a similar age. A quote that prices each unit separately lets you decide which to replace now and which to leave.
Sources
- When to repair or replace your windows – Glass and Glazing Federation
- Approved Document K: Protection from falling, collision and impact – GOV.UK
- Windows and doors: building regulations – Planning Portal interactive guide
- BS EN 12150-1:2015+A1:2019 Thermally toughened soda lime silicate safety glass – BSI
- Energy efficient windows and doors – Energy Saving Trust
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