Condensation

[JoeyB]

During frosty nights/mornings my north facing Bay windows get condensation on them .Even if the rooms are empty.
They are double glazed,perhaps 10 years old or more.
How can I prevent this.

[RATTER15]

If the room is empty, could you leave a window open, condensation only occurs in a warm atmosphere, warm air will carry a lot of moisture but when the warm air come into contact with a cool surface ie a window, the warm air releases the moisture onto this surface, so the air in a cold room will carry little moisture. or keep some heat near the window.

[kwicky]

We had this problem in our old house. We cured this by attaching to the windows sheets of cling film.

[KARL]

I find this rather puzzling, unless the indoor atmosphere is particularly humid - a correctly calibrated hygrometer will tell you what it actually is - or else the double glazing is not sealed or the seal has failed (you don't suggest this). One other reason might be if the rooms are heated by some means that leave high humidity levels (i.e. not conventional central heating). On the other hand, if you have closed curtains at the windows then the air trapped between them and the glass will cool significantly, dump its moisture onto the coldest surface (the glass) and sink to the floor and into the room under the curtains. This air is replaced from the top by more warm and humid air which cools, dumps its moisture, etc. - condensation builds up. If a radiator is positioned under the window in each case, this cycle is broken (in fact the flow is reversed and the glass dried off) and not only do you avoid condensation but the draught from the window disappears. If a radiator is positioned away from the window (especially furthest away from it) the cycle is accelerated: the heated air rises from the radiator at the far wall to the ceiling along which it travels to the window and then plunges to the floor. That configuration acts as a slow speed fan creating a draught. This is why radiators should be positioned directly below windows unless utterly impossible. It is a fallacy to think they should be at doorways except for the external door - unless perhaps only one room is heated (then two, one at the door the other at the window). If the whole house is heated at the outside perimeter then the heart of it will automatically be warm.

[KARL]

Sorry, forgot to say our north facing windows have K-glass units and a shaped radiator under the bay, others flat and also directly below. These windows never show the slightest hint of condensation even when freezing conditions occur. Never any curtains drawn.