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Can anyone give me some info on the effectiveness of a condensation unit. We have a problem with condesation and mould in a 1930's bungalow which we've extened and renovated. We've had new windows with trickle vents which are open 24/7, humidistat fans , use a dehumidifer, follow all the correct guidelines etc, but still have mould on walls and high water levels on windows nearly every day. We've had various damp companies out and been told we don't have damp walls, (just narrow cavities with old cavity wall insulation) one suggested a condensation unit which is installed in the loft and has only one vent in the ceiling, my concerns is how can one vent effectively circulate the buildings warm air in all the rooms and is it worth the money as my theory is the warm moist air will still be at a high level causing more mould when the room temp drops !

I expect this only happens in the winter?
I expect it is due to turning the heating off or down when you go out or go to bed.
Warm air, say at 20 C holds 18 ml per cubic metre.
Cold air 0 C is almost dry 5 ml per cubic metre.
Every time you let the indoors temperature drop, the water vapour in the air falls out.
It condenses onto/into the nearest cold object/surface, usually a window but, if you have double glazing, maybe the walls, or the window reveal.
Your bed probably feels cold, because it is full of cold moisture.
Each of us sweats 330 ml of water every night, that goes straight into the bed.

The solution.
Make sure you have an extractor fan in the kitchen and bathroom and use it when cooking or washing, and keep the kitchen and bathroom doors closed at all times.

Do not dry things on radiators.

Next. Every time we breath out our breath is saturated with water - breath on a mirror and see it in action.
This moisture needs to be vented to the outside. Outside air is usually drier than indoors.
We each breath out 1.5 litres of water per 24 hours, children and animals more.
Either open the windows for 5 mins or so every morning and evening, or use a dehumidifier, that can remove 5 litres or more of moisture per 24 hours.
Leave the dehumidifier on 24 hours a day
in about 3 weeks you will see a difference
in a year the dehumidifier will hardly come on at all.

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