Blown Double Glazing: The Cost to Replace the Glass

If one of your windows has gone cloudy or misted between the panes, you have blown double glazing, and the good news is you often do not need a whole new window. The double glazing glass replacement cost is usually a fraction of a full replacement, because you are only swapping the sealed glass unit inside the existing frame. This guide explains what it costs, why units blow and when replacing the glass is the smart move.

What "blown" double glazing means

A double glazed pane is really a sealed unit: two sheets of glass with a spacer and a dry, insulating gap between them. When the seal around that unit fails, moisture creeps in and cannot get out. That is why you see misting, cloudiness or little droplets trapped between the panes that no amount of cleaning will shift.

The frame and the opening mechanism are usually fine. It is just the sealed glass unit that has failed, and that can be replaced on its own.

Double glazing glass replacement cost

As a rough 2026 guide, supplied and fitted, replacing a single blown sealed unit typically costs:

• A small to medium standard unit: roughly 60 to 150 pounds.
• A larger unit: roughly 150 to 300 pounds.
• Units with special glass (toughened, laminated, obscure, decorative or coated): often 200 to 450 pounds or more.

Compare that with 400 to 900 pounds for a whole new uPVC window, supplied and fitted, and you can see why replacing just the glass is the cheaper fix when the frame is sound. Prices vary with size, glass type and access, so get a quote for your own window before budgeting.

Why sealed units blow

Sealed units fail for a few common reasons:

• Age: most units last a long time, but the seal does not last forever, and older ones eventually go.
• Trapped water on the sills: poor drainage or blocked frame vents can sit water against the unit and stress the seal.
• Heat and sun: south-facing windows expand and contract more, which works the seal harder over the years.
• Fitting or handling damage: a knock or a poorly seated unit can shorten its life.

A single blown unit does not mean the rest of your windows are about to go. Often it is just that one, and swapping it sorts the problem.

Replace the glass or the whole window?

Replacing just the sealed unit makes sense when:

• The frame is in good condition, opens and closes properly and locks securely.
• Only one or two panes have blown, rather than the whole house.
• The window is fairly modern and you are happy with the style.

A whole new window is the better spend when:

• The frame itself is tired, draughty, discoloured or the mechanism is failing.
• Several windows are blown and near the end of their life anyway.
• You want to upgrade the style, colour or energy performance while you are at it.

If you are not sure which camp you are in, that is exactly the kind of thing our team sorts out on a visit. We handle window and door repairs, and we will tell you honestly when a glass swap is enough and when a new window is the better value. If a full replacement does turn out to be the answer, our uPVC windows range shows the options.

How the repair works

Replacing a sealed unit is a tidy job. The fitter measures the failed unit, orders a matching one made to size, then removes the beading, takes out the old glass and fits the new unit sealed and square. Most single-pane swaps are done in well under an hour once the glass is ready. There is no plastering or making good, because the frame stays put.

FAQs

How much does it cost to replace blown double glazing?

As a rough 2026 guide, a single blown sealed unit typically costs 60 to 300 pounds supplied and fitted, depending on size, with special glass costing more. That is far less than a whole new window, so replacing the glass is usually the cheaper fix when the frame is sound.

Can you replace just the glass in a double glazed window?

Yes. When the seal fails and the unit mists up, the sealed glass unit can be swapped on its own while the frame stays in place. It is a common repair and much cheaper than replacing the whole window, as long as the frame and mechanism are in good order.

Why has my double glazing gone cloudy between the panes?

The seal around the sealed unit has failed, letting moisture in that cannot escape, which shows as misting or cloudiness. Cleaning will not fix it because the moisture is trapped inside the unit. Replacing the sealed unit clears it up.

Is it worth repairing blown double glazing or replacing the window?

If the frame is sound and only a pane or two have blown, replacing the glass is the cheaper, sensible fix. If the frames are tired, several units have gone, or you want to upgrade, a new window may be better value. A quick look will tell you which.

Want us to take a look at a misted window? Download our latest brochure for the full range, or request a free quote and we will pop out and check it over.