Repairs
Misted double glazing: repair or replace?
Misting between the panes means the seal has failed. Usually the fix is a new glass unit in your existing frame.
If you can see condensation or a cloudy film between the two panes of glass, the sealed unit has failed. It is one of the most common double-glazing faults, and usually one of the simplest to put right.
- Moisture you cannot wipe off from either side means the seal on the glass unit has failed.
- The lasting fix is a new sealed unit made to size and fitted into your existing frame.
- Drill and dry may clear the view for a while, but it does not restore the seal or the gas.
- Replace the whole window only if the frame, hinges or locks are failing too.
First, check where the moisture is
- Condensation on the room side of the glass comes from humidity indoors. Wipe it off and improve ventilation.
- Condensation on the outside of the glass on cold mornings is normal with efficient glass. It shows less heat is escaping through it.
- Moisture between the panes that you cannot wipe off from either side means the unit has failed.
Why sealed units fail
A sealed unit is two panes of glass held apart by a spacer bar and bonded with a seal around the edge. The spacer contains a desiccant that soaks up any moisture trapped inside.
Over years of heating and cooling, the edge seal can break down. Damp air gets in, the desiccant fills up and condensation forms between the panes. Blocked drainage in the frame speeds this up, because the bottom edge of the unit ends up sitting in water.
Does it matter?
It spoils the view, and it will not get better on its own. Once the seal has gone, the unit has usually lost some or all of its argon, so it lets more heat through. Left for years, the inside of the glass can stain and stay cloudy for good.
Your options
Replace the sealed unit
A new unit is made to measure and fitted into your existing frame. This is the lasting repair. It is also a chance to upgrade to Low-E glass, argon and warm-edge spacers, or to change the glass, for example to obscure glass in a bathroom. If the pane is within 800 mm of the floor, or in or beside a door, the new unit should be safety glass.
Drill and dry
Small holes are drilled in the glass to dry out the cavity, then plugged. It may clear the view for a while. It does not restore the edge seal or the gas, so we do not recommend it.
Replace the whole window
Only worthwhile if the frame itself is failing, the hinges and locks are worn out, or you are replacing other windows anyway. See our window range if that is the case.
What we need for a price
- A photo of the misted pane
- The rough width and height of the visible glass, in millimetres
- Whether it is in a window or a door, and which floor it is on
- Any details to keep, such as Georgian bars or leaded lines
The exact unit size is checked before the glass is ordered. To stop it happening again, keep the drainage slots clear. Our care guide shows how.