Misted Double Glazing — Repair or Replace?

If your double-glazed window has gone misty or cloudy between the panes, here's what's actually happening — and what your options are.

Why does double glazing go misty?

Double-glazed windows work by trapping a layer of inert gas (usually argon) between two panes of glass. This sealed unit acts as an insulating barrier. When the seal fails — which happens gradually over time — moisture gets in between the panes. As the temperature changes throughout the day, this moisture condenses, causing that characteristic cloudy or streaky appearance.

Once the seal has failed, the condensation isn't going away on its own. The only fix is to replace the sealed glass unit. See our glass replacement service for full details.

Do I need to replace the whole window?

In most cases, no. This is the most important thing to understand — a misted window doesn't mean you need a new frame. If the uPVC or aluminium frame is still in good condition (not cracked, warped, or poorly fitting), you only need the glass unit itself replaced.

This is significantly cheaper than a full window replacement:

We'll always tell you which option makes sense for your window. If the frame is in good shape, replacing just the glass unit is the right call — there's no reason to spend more than you need to.

How is a sealed unit replaced?

The old glass unit is carefully removed from the existing frame. A new factory-made sealed unit — cut to exactly the right size — is fitted in its place, re-sealed, and re-beaded. The whole job typically takes 30–60 minutes per window.

The new unit has the same argon-filled gap and the same thermal performance. Qualifying units carry a 10-year manufacturer warranty when installed into uPVC or aluminium frames, or a 5-year manufacturer warranty when installed into timber frames.

What if my frame is also in poor condition?

Sometimes a misted window is the visible symptom of a wider problem. If the frame is:

• Cracked or warped
• Letting in draughts even when closed
• Very difficult to open or close
• More than 20–25 years old

…then a full window replacement may make more financial sense. We'll tell you honestly when that's the case. We're not going to push you towards the more expensive option if it isn't warranted.

Can misted glass be repaired without replacing it?

You may have seen adverts for services that drill a small hole in the glass, pump out the moisture, and inject a desiccant. These exist, but we don't offer this service — and we'd be cautious about recommending it.

The reason: drilling the glass doesn't fix the failed seal. Moisture will continue to get in. The improvement tends to be temporary. A replacement sealed unit gives you a properly sealed, warrantied result that will last another 20+ years.

How long does a sealed glass unit last?

A new sealed unit, properly installed, should last 20–25 years before the seal begins to fail. The factors that affect longevity are mainly exposure (south-facing windows in direct sunlight experience more expansion/contraction) and the quality of the original installation.