Preventing damp and condensation

ThisIsWeird

Postik said:

Thanks - all makes sense.  Although I must confess I have the extractor on whilst showing (and a couple of hours after finishing) but when I leave the room I also open the window.  I feel that the extractor can sometimes struggle with the sheer amount of steam and an open window helps to clear things more quickly.  At my old house we had an extractor which we used religiously, but still suffered mould on the ceiling after a few years.  I was convinced this came about in the winter when we showered without the window open due to the cold.

I don't think there's a hard and fast rule. A lot will depend on the location of the extractor, how effective it is, and where the window is located.

Just bear in mind that windows don't just allow out air, but can let it in - it depends on wind direction! So, if it's blowing in, then that moist air is heading into your house.

Also, an open window might make it appear that it's cleared the room more quickly, but it could as easily have just cooled the air, so the moisture has condensed out - on to the walls and ceilings...

But, it might also work very well!

I use my mirror as a guide on what's going on - if that clears, then I know the rest of the room is following suit.

Extractors cost next to nothing to run, so leave it running for as long as you need to!

GrubbyGirl_2

Opening the window can mean you're letting more moisture in than out, much depends on the weather outside.  I have an outside thermometer which also records humidity and at the moment it's not raining but still showing 78% humidity, if it's raining this can be 90% plus.  When I have a shower my bathroom goes up to 75% so opening the window wouldn't improve anything that a bit of heat would

Swipe

GrubbyGirl_2 said:

Opening the window can mean you're letting more moisture in than out, much depends on the weather outside.  I have an outside thermometer which also records humidity and at the moment it's not raining but still showing 78% humidity, if it's raining this can be 90% plus.  When I have a shower my bathroom goes up to 75% so opening the window wouldn't improve anything that a bit of heat would

You are overlooking the fact that the outside air is at 78% relative humidity which is determined by how much water vapour it can hold at a certain temperature. Once that 78%RH air enters the house and warms up it might well suddenly become 50% relative humidity.

ThisIsWeird

Swipe said:

GrubbyGirl_2 said:

Opening the window can mean you're letting more moisture in than out, much depends on the weather outside.  I have an outside thermometer which also records humidity and at the moment it's not raining but still showing 78% humidity, if it's raining this can be 90% plus.  When I have a shower my bathroom goes up to 75% so opening the window wouldn't improve anything that a bit of heat would

You are overlooking the fact that the outside air is at 78% relative humidity which is determined by how much water vapour it can hold at a certain temperature. Once that 78%RH air enters the house and warms up it might well suddenly become 50% relative humidity.

Thanks for that explanation, Swipe.
D'oh - I know from experience that having a window venting on any day will help to keep a room dry, but hadn't twigged on that explanation of why it still works on stinking wet days!
We pass through this holiday-home farm on one of our fav walks, and they have a large open car port which also has their laundry machines in it. Even on the dullest, wettest, dankiest days, tipping it down, that whole area is bone dry, as are the cars, as are the washing machines. No condensation on them at all.

GrubbyGirl_2

Swipe said:

GrubbyGirl_2 said:

Opening the window can mean you're letting more moisture in than out, much depends on the weather outside.  I have an outside thermometer which also records humidity and at the moment it's not raining but still showing 78% humidity, if it's raining this can be 90% plus.  When I have a shower my bathroom goes up to 75% so opening the window wouldn't improve anything that a bit of heat would

You are overlooking the fact that the outside air is at 78% relative humidity which is determined by how much water vapour it can hold at a certain temperature. Once that 78%RH air enters the house and warms up it might well suddenly become 50% relative humidity.

Except if you read the other post she doesn't have the heating on so the flat is around 9 degrees so there isn't much heating going on

Effician

GrubbyGirl_2 said:

Swipe said:

GrubbyGirl_2 said:

Opening the window can mean you're letting more moisture in than out, much depends on the weather outside.  I have an outside thermometer which also records humidity and at the moment it's not raining but still showing 78% humidity, if it's raining this can be 90% plus.  When I have a shower my bathroom goes up to 75% so opening the window wouldn't improve anything that a bit of heat would

You are overlooking the fact that the outside air is at 78% relative humidity which is determined by how much water vapour it can hold at a certain temperature. Once that 78%RH air enters the house and warms up it might well suddenly become 50% relative humidity.

Except if you read the other post she doesn't have the heating on so the flat is around 9 degrees so there isn't much heating going on

Maybe not much heating going on but enough to have a big impact on RH,  lets say 2c outside with 95%RH ,sounds fairly high doesn't it but even raising that same air to 9c will drop the RH to 60%.

A handy little calc to try out if you wish  https://www.calculator.net/dew-point-calculator.html