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Advice please on possible faulty upvc window

Joined
19 Sep 2025
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Hi everyone,

I need some advice please. I have a north facing living room upvc window, which sits in a deep recesssed area (see photo).

That side of the house gets limited sunshine, as the sun is mainly on the rear of the house. We have lived here for 2 years and in that time have noticed that during cold weather the whole window (and smaller side panes) condense very easily. Most mornings we have to use a window vac to remove the condensation.

We have the heating on for an hour in the morning and a few hours in the early evening, I think the temperature in the room is fine, just the humidity is too high.

As I write this I have a dehumidifier running, which has an auto shut off but has been running for the last 4hrs.

Last year we had kingspan installed under the windowsill outside and the insulation renewed under the tiled overhang roof above the window. This has made no difference.

The photo attached shows a dry area in the shape of a ‘V’ in the middle of the large pane, which lends me to think the window is failing.

Washing is put to dry in our conservatory on an airer with a dehumidifier running, to help the drying.

Any clues or suggestions please on the window condensation?

Thanks

Paul

IMG_8937.jpeg
 
The bay window design means the glass gets colder more easily, as warm air from your radiator won't go into the bay.

If you are drying clothes nearby, then you are increasing humidity which exacerbates this problem. Do you have any ventilation like a trickle vent or something? Do you crack open any windows when you are drying clothes?

So, in summary, poor bay window design + drying clothes indoors + possible lack of ventilation is the problem.
 
Thanks for the reply, however there is no washing drying in the open plan living/dining room. All washing is dried in the conservatory which is 3 rooms away from the living room with a dehumidifier running (if the washing isn’t drying outside).

Your theory about the heat loss is feasible, as it’s a deep recessed window, and it does feel like a cold area when you put your head in the recess. When we close the curtains in the evening I hoped the heat from the radiator finds its way into the recess but I guess not.

Just weird how the window doesn’t condense in that area in the middle.

Thanks

EDIT - Sorry forgot to also mention that the window in question does not have a trickle vent as it’s the type that was installed before they became commonplace. We do put them on vent (ie open slightly) periodically, but obviously not when it’s freezing outside.
 
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