Blown Double Glazing & What To Do About It

One of the most common problems that people have with their double glazed windows is mist, fog or condensation in between the two panes of glass. If you are seeing this between your window panes, it means that your double glazing units seals have failed. This is what is known as a blown double glazing. This article will help you identify how you can repair blown double glazing.

Why is there condensation inside my double glazed windows?

Double glazing, sealed units, or Integrated Glass Unit (IGU) are the names given to what is often referred to as double glazing. The windows are made by placing two panes of glass together with a thermally efficient spacer bar in between filled with desiccant that is thermally efficient. This unit is then sealed to make it into a double glazed sealed unit. When the seal on the double glazed unit breaks (or “fails” the industry term) that condensation will get into the inside of the glass unit, resulting in misted or blown double glazing. If the seal is broken, then solar pumping (a term for when air can get trapped inside the window occurs).

This is one of our customers windows before he attempted the repair!

The window expands with warm air and contracts with colder moist air and as air contains microscopic droplets of water, these then get trapped inside with unit when the seals start to fail. All double glazed units will fail at some point, there are only a number of times the windows can expand / contract before the seals fail. When this happens the moisture in the air gets trapped, which is picked up by the desiccants stored within the window frames. Once this desiccant is filled with extracted moisture, the rest of the moisture has nowhere else to go, so this is when you see it as mist or fog which is what you see forming as condensation between the panes of glass.

Can I ignore my blown double glazing? What effect will it have?

Aside from the obvious issue of the condensation obscuring the clear view from your windows, blown double glazing will interfere with the energy efficiency of your windows. If the seal has broken, the window is no longer sealed, so it will not be performing the function of a sealed double glazed unit; it can no longer keep the cold out, and as water is a good conductor of heat the condensation inside your windows will drastically reduce the thermal efficient of your windows. The second problem is that if the condensation is left inside the window, eventually the minerals within the water will harden and you will see white streaks / dried on baked marks on the window. Once the window has reached this stage the glass unit will have to be replaced, a costly exercise, if you don’t repair blown double glazing.

If you have moisture inside your window, the time to fix it is now, as the longer you leave it the more chance you have of having to replace the glass. As mentioned above water is a good conductor of heat so fixing the unit removes the moisture and you’ll regain most of the original thermal efficient as the dry air inside a repaired blow unit is a poor conductor of heat therefore giving greater thermal efficiency.

Can and how to repair blown double glazing be repaired?

Yes is the answer, blown double glazing can be repaired, to solve this fourfold problem, we need to do just three things:

  1. We need to pressure equalise the unit by drilling two tiny holes, so that the seal on the unit doesn’t open when the sun comes out.
  2. We need to create an environment so that the moisture instead of turning into vapour when heated by the sun will evaporate.
  3. We need to install a tiny plug that will keep the air inside the unit to create a thermal barrier, but will also allow air to pass when placed under pressure.

The Condensation2Clear Window Repair Kit includes everything you need to fix this problem in a simple DIY kit. This can be fixed for <£5 per window.

This was one of our customer’s windows after he attempted the repair!


Do I need to replace the window frames as well?

No, you don’t need to touch the frames as the Condensation2 Clear window repair kit fixes the glass unit, the frames don’t need to be touched.

What causes condensation on the outside of the double glazed unit?

When you see condensation on the side of your double glazing that faces the room, it indicates a ventilation issue in that specific space that requires attention. Inside the unit, condensation can form if you’re drying clothes in a space, especially during damp and chilly conditions. If there’s condensation on the outside, it means your double glazed window is functioning correctly, and this moisture will typically vanish as the day warms up. This is a regular occurrence, not a defect in the window or glass, and it’s unrelated to any double glazing issues mentioned previously. This mostly happens in Spring and Autumn when nighttime glass temperatures drop, causing moisture from the morning dew to condense on the glass’s cooler surface.

See our YouTube videos here for an introduction to Condensation2Clear, our team, and how this kit works.

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