Condensation in Double Glazing - How to Stop Fogged Double Glazing

Summary: Condensation in double glazing; how to stop misting in double glazing. This one of the most common double glazing problems so it is worth understanding how water gets into double glazed windows and what can be done to resolve it. Often a sealed unit needs to be replaced and this project gives you some information about tackling this job.

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Misting or Fogging of sealed units in double glazed windows is a common problem and most often occurs after the guarentee on the units has passed! Misty or Foggy windows can make a room look awful but repairing or replacing the sealed units is no longer a big problem.

The panes of glass used in double glazed windows are called sealed units. See our double glazing project for more about these. The panes are held apart by hundreds of tiny silica balls which are held in a spacer bar. These are the same as the balls what you often find in the little bag you receive when buying electrical goods, They are also found in the trays bought from DIY stores which are placed on window sills to prevent condensation.

These silica balls absorb any moisture in the air between the two panes of glass ensuring that it remains dry and therefore stops condensation.

These same balls can be found in the little bag you receive when buying electrical goods and also in the trays bought from DIY stores which are placed on window cills to prevent condensation.

It is these balls which soak up any moisture which exists in the air between the two panes of glass.

Once the silica becomes saturated the moisture in the air will begin to mist, or fog up your double glazing.

This should not happen for at least 5 years from the date of installation and you should have a receipt from your double glazing company to guard against sealed units "breaking down". Most companies offer a 10 year guarantee.

The condensation and misting is a natural process in an old sealed unit and if it is past the sell by date, is nobodys fault. If the unit breaks down prior to the guarantee running out then the sealed unit should be replaced by the supplier.

It is now possible to rectify a broken down sealed unit. A small hole is drilled in the glass (can be done from outside in most cases) and a tiny vent installed. This job requires specialist equipment and is not a DIY task. It is certainly worth finding out about in your area as most of the repair companies state that up to 50% can be saved on the cost of a replacement sealed unit.

Removing a sealed unit is done by inserting a sharp scraper, or chisel, into the joint between the glazing bead and the frame and twisting while keeping the pressure on. The bead will clip out. Make sure you have the correct spacers in the frame when you put the new unit back.

Don't fancy doing this project yourself? We work with Checkatrade to ensure that we recommend only reliable and trustworthy tradesmen.

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