The short answer
The clearest signs you need new windows are persistent draughts, misting between the panes, frames that stick or won’t lock, visible rot or damp around the reveal, and rising heating bills. A single misted unit can often be fixed with a glass-only swap, but when several problems combine — especially failing frames and hardware — replacement is usually the better long-term call. Most windows last 20–35 years, so age is a useful guide alongside the symptoms.
Windows rarely fail all at once; they decline gradually, and it can be hard to know when repair stops being worthwhile and replacement becomes the sensible choice. This guide runs through the signs to look for, explains which can be fixed cheaply and which point to replacement, and helps you judge where your windows sit on that scale.
Warning signs at a glance
- Misting between the panes Sealed unit failed
- Draughts you can feel Seals or frame failing
- Sticking or jamming frames Warping or movement
- Rot, soft timber or damp Frame failure
- Condensation on the inside Poor insulation / ventilation
- Rising heating bills Heat loss through windows
The signs that point to replacement
Some symptoms are minor and fixable; others tell you the window itself is failing. The strongest indicators that replacement — rather than repair — is due include:
- Draughts you can feel around a closed window, meaning the seals or the frame have failed.
- Frames that stick, jam or won’t lock, a sign of warping, swelling or movement that is hard to reverse.
- Rot, soft timber, brittle or discoloured uPVC, or damp around the reveal — the frame is past its serviceable life.
- Multiple misted units across the house, suggesting windows of a similar age all reaching seal failure.
- Noticeably higher heating bills or rooms that never feel warm, where old single or early double glazing is letting heat out.
| Sign | Likely fix |
|---|---|
| One misted unit, sound frame | Replace the glass only |
| Draught from a single seal | Re-seal or replace seal |
| Sticking frame, warped | Replace the window |
| Rot or damp in the frame | Replace the window |
| Many failed units, old windows | Phased whole-house replacement |
Signs that can be repaired instead
Not every problem means new windows. A single misted or cracked unit in a sound frame can be fixed with a sealed-unit replacement for £60–£200. A draught from one perimeter seal can sometimes be re-sealed. A handle or hinge can be replaced without touching the rest of the window. The deciding question is the condition of the frame and hardware: if those are good and only the glass or a seal has failed, repair is the economical route. If the frame and hardware are failing too, you are repairing a window that is on its way out.
How age factors in
Most double glazing lasts 20–35 years, with sealed units sometimes misting from around 10–20 years — see how long double glazing lasts. Age alone is not a reason to replace working windows, but if your windows are at or beyond that range and showing several of the signs above, replacement is likely to be the better investment than a series of repairs. New windows also bring a better energy rating and a fresh guarantee. This is general information; an installer’s on-site assessment is the best way to judge the condition of your specific windows.
Compare double glazing quotes
If the signs point to 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
When should I replace my windows?
Consider replacement when you have persistent draughts, frames that stick or won’t lock, rot or damp in the frame, multiple misted units, or rising heating bills — especially if the windows are 20–35 years old. A single fault in a sound frame can usually be repaired instead.
Is condensation a sign I need new windows?
It depends where it is. Misting between the panes means a failed sealed unit. Condensation on the inside (room side) usually points to indoor humidity and ventilation, not a failed window. Condensation on the outside is normal and a sign of good insulation.
Can old windows be repaired rather than replaced?
Often, yes — a misted unit, a worn seal or a failed handle can be fixed individually. Repair is the economical choice when the frame and hardware are sound and only the glass or a seal has failed.
How do draughty windows affect my heating bills?
Draughts and poor insulation let heat escape, so your heating works harder to keep rooms warm. Replacing failing windows with a good energy rating reduces heat loss, though the exact saving depends on your home and how it is heated.
Sources & further reading
- Glass and Glazing Federation (GGF) — window condition, condensation and consumer guidance
- Energy Saving Trust — windows, heat loss and energy efficiency
- FENSA — replacement windows and registered installers
- GOV.UK / Building Regulations Approved Document L — thermal standards for replacement windows
This is general information, not advice for your specific property or installation. 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.