The short answer
Yes — in most cases you can replace just the sealed glass unit and keep the existing frame, typically for £60–£200 per unit. This works when the frame, hinges, handles and locks are all sound and only the glass has misted, cracked or failed. If the frame itself is rotten, warped or the hardware is failing, replacing the whole window usually makes more sense. A glass-only swap is far cheaper than a new window and keeps disruption to a minimum. See misted or blown double glazing for the common reason units fail.
Many people assume a foggy or cracked double glazed window means buying a whole new window. Often it does not — the glass and the frame are separate, and the glass can usually be replaced on its own. This guide explains when a glass-only replacement is possible, what it involves, and the cases where the whole window is the better buy.
Glass-only replacement at a glance
- Cost per sealed unit £60–£200
- Possible when Frame and hardware are sound
- Time on site Often under an hour per unit
- Lead time A few days to make the glass
- Energy rating Can match or improve the original
- Not suitable if Frame is rotten or warped
When a glass-only replacement works
A double glazed window is made of two parts: the frame and the sealed glass unit that sits inside it. If only the glass has a problem — misting between the panes, a crack, or a chip — and the frame is in good order, the installer can simply swap the sealed unit. They remove the beading that holds the glass, lift out the old unit, and fit a new one made to the same size and specification. This keeps the existing frame, sill and reveal untouched, which is why it is so much cheaper and quicker than a full window replacement. It is the right choice for a relatively modern window that has suffered a single fault.
| Problem | Glass-only fix? | Notes |
|---|---|---|
| Misted / blown unit | Yes, if frame sound | Most common reason |
| Cracked or chipped pane | Yes, if frame sound | Swap the affected unit |
| Draughty, rotten frame | No | Replace whole window |
| Failing hinges / locks | Usually no | Hardware or window replacement |
What to check before you order glass
Before paying for a sealed-unit swap, an installer should confirm that the frame is genuinely sound: no rot in timber, no brittleness or discolouration in older uPVC, and that the opening mechanism, hinges and locks still work properly. There is little point fitting new glass into a frame that will need replacing within a year or two. It is also worth matching or improving the glass specification — a modern low-emissivity, gas-filled unit can give a better Window Energy Rating than the original. See window energy ratings explained to understand what to ask for.
When the whole window is the better buy
If the frame is rotten, warped, badly discoloured or the hardware is failing, fitting new glass is a false economy — you would be investing in a window that is itself near the end of its life. The same applies if many units across the house have failed at once, which often means windows of a similar age reaching seal failure together; in that case a phased whole-house replacement may be more cost-effective and gives you a fresh guarantee on everything. See signs you need new windows for the full checklist. This is general information; whether a glass-only swap is right depends on the condition of your specific windows.
Compare double glazing quotes
For a single sealed unit or a full window replacement, comparing quotes helps you get a fair price. Use our service to reach FENSA or CERTASS registered installers in your area.
Frequently asked questions
Can you replace a double glazed unit without replacing the frame?
Yes. The sealed glass unit and the frame are separate, so if the frame is sound an installer can remove just the glass and fit a new unit of the same size, typically for £60–£200.
Is it cheaper to replace the glass or the whole window?
Replacing just the glass is much cheaper — £60–£200 per unit versus £400–£900 for a whole uPVC window. It only makes sense, though, if the frame and hardware are in good condition.
How long does it take to replace a sealed unit?
Fitting itself often takes under an hour per unit once the glass is made. The main wait is the few days it takes to manufacture the new unit to the correct size and specification.
Can I upgrade the glass when I replace a unit?
Yes. You can specify a higher-performance sealed unit — for example low-emissivity, gas-filled or acoustic glass — which can improve the Window Energy Rating or noise reduction compared with the original.
Sources & further reading
- Glass and Glazing Federation (GGF) — sealed unit replacement and consumer guidance
- FENSA — guarantees, registered installers and replacement glazing
- Energy Saving Trust — double glazing performance and glass specifications
- GOV.UK / Building Regulations Approved Document L — thermal standards for replacement glazing
This is general information, not advice for your specific property or installation. Costs and outcomes vary with your windows and chosen installer. Replacement windows should be fitted by a FENSA or CERTASS registered window installer. We are an independent information and introduction service, not an installer.