Condensation on new replacement glass

29 Dec 2014
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United Kingdom
Slightly confused :)

Old double glazing units, 28mm, and one of the top small window panes had failed with internal condensation within the pane. Other panes all OK

Had the pane replaced last week and it is clear, however it, and only it has had condensation on it the last two mornings. The condensation is on the OUTSIDE (external) side of the glass.

If the unit was badly made, I'd have expected condensation on the room side of the glass?

The window is south facing and it has been cool overnight.

So why this unit only? Could it be its the only one that is "clean" externally? :eek:
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Condensation forms when moist air comes into contact with a colder surface.

If the new sealed unit has condensation on the outside and the others don't, that will be because it has a colder external surface than the others.

This is probably because the new sealed unit offers better insulation than the existing units and less heat is being transmitted to the exterior glass from inside your home.

As we get into winter properly and the present warm moist weather ends, you will find the external condensation will also.
Good explanation. Sh*t. Does that mean I'd get better insulation if I replace all the other windows lol. Would be good to get a thermal camera on to see the difference. Probably not worth it though :)

It became a common issue when warm edge double glazing came in with soft coat low e -the unit is doing its job and stopping the warmth from getting to the external pane of glass -which on cold mornings just happens to be the coldest bit of the building material , so it gets condensation.

Its a bit like a well insulated roof keeps the snow longer on it longer!
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Not much else to say, notch explained it pretty well - its how modern units work, the morning sun soon burns the dew off, this phenomenon caused quite a few queries and complaints a few years ago when it first became apparent

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