Misted Double Glazing: Repair or Replace?

Misted units are the most common glazing fault in UK homes, and the market has grown a small industry of de-misting services around it. Here is the honest comparison.

What de-misting does

A technician drills small holes in the outer pane, flushes or vents the cavity, and fits one-way valves. The visible mist usually clears within days. What it cannot do is restore the argon fill, recharge the desiccant, or close the failed seal — the unit is still breathing humid air with every temperature swing.

What replacement does

The frame stays put. A glazier removes the beads, lifts out the failed unit and fits a new one — typically under fifteen minutes a window. You get fresh seals, new desiccant, gas fill and the option to upgrade the glass specification at the same time.

The numbers

De-misting typically costs a little less per window up front. But treated units commonly mist again within a couple of years, and the insulation never recovers — a unit that has lost its argon and gained moisture can run well above its rated U-value. Replacement resets the clock entirely, and modern units carry our 5-year warranty.

When repair makes sense

• A listed building where glass must be preserved exactly as-is
• A short-term fix before a planned full refurbishment
• Access equipment already on site for other work

For everything else, price a straight swap first — use the instant quote calculator to see trade pricing before you decide.