Black mould and condensation

[88v8]

Good news.

Drying out of the air is quick. Drying out of the building fabric, the woodwork, the walls, will take months.
If you have good original joinery, I'd be cautious in going below 50% this winter, as accelerated drying may cause cracking of the woodwork. Same applies to any antique furniture.
40-50% RH is comfortable long-term, and not detrimental to the building.

You're right though to focus on extractors. The dehumidifier alleviates the symptoms, but extraction will remove a lot of the cause.

Ivor

 

[tobydog]

We're somewhat lucky that our well insulated boiler room can get pretty hot and we can use it for drying clothes on a wet day. In the winter we simply turn the extractor fan on and this takes out the moist air at a rate slow enough for the warmth to still be maintained by the boiler. In the warmer months, when the heating isn't on, we simply put the dehumidifier in there on laundry mode and leave the fan off. Both methods ensure that no excess moisture gets into the main house. We're pretty sure it doesn't because we have a very old cottage and the windows are single glazed. If we forget the fan in the winter, it soon shows up on the windows.

I should point out that the boiler room gets hot not just because of the insulation (it's in the new extension). In the winter, because the pipework to the large kitchen under floor heating runs on constant mode, the exposed pipework / valve system is continually giving off heat. I could lag some of them but the heat is very useful. On winter days when we're not drying clothes I can open the door and the heat helps warm the house.