window vents and condensation

24 Nov 2010
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United Kingdom
can anyone help.

we moved into our 1960s home in july and are generally very happy with it.

however we have tired / broken vents in all the double glazed pvcu windows whch cause increased noise and droughts. the windows now have condensation on them (severe in the master bedroom) scince the weather has become colder.

we have investgated the condensation problem and found conflicting answers....we have plenty of ventilation as the windows are well ventilated, so why are we getting condensation ?

we were also told that because the vents let cold air through, it cools the air and windows in the room, causing the cold surface to cause condensation.

we would like to block the window vents to stop the cold droughs, any ideas how to? we are also concerned that it may cause more condensation, but it is already there so we can't see how it can get worse.

thank you for any ideas

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I am not an expert but I wouldn't block them and that is what they were put in there for.
what you have isnt ideal as the cold airflow in that specific area is causing a cold spot on the coldest surface in the room

what you need is ventilation either by opening the window or via wall vents away from the window then you can consider reducing the vents assuming they are large rather than trickle vents
Blocking off the vents & reducing ventillation is likely to have the opposite effect & increase condensation. Here a copy of a post I just made on another thread, not all may be relevant but you should get the picture;

Condensation is caused by & in no particular order;

Old inefficient double glazing
New efficient double glazing with no natural ventilation
High ambient moisture content inside the home
Drying washing indoors
Moisture generated by cooking, bathing, breathing not being able to escape
No forced ventilation (fans) in kitchen/bathroom/utility rooms
Lack of natural ventilation
Insufficient background heating
Inappropriate heating – paraffin or LPG heaters generate tremendous amount of moisture
Possible damp penetration through the walls

Moisture must be allowed to escape somehow or it will condense on the coldest surface in the room. It’s important to have one window in each used bedroom & the main living area slightly open for at least a couple of hours a day &, as you’ve found, it will clear. Have you tried leaving a window in each used bedroom slightly open at night, fresh air never killed anyone & human beings exhale a great deal of moisture overnight. A slightly higher ambient temperature overnight will also help, switching heating off completely for 6 hours wont will reduce the dew point significantly. Here’s a link for you to read;
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