Positive input ventilation

[anyunusedpassword]

Hello,
Our house is damp and has mould growing on walls and furniture. We have 2 dehumidifiers running almost 24/7 , have trickle vents constantly open in all rooms, dry very little washing indoors and have extractor fans in shower room and kitchen. I’ve recently seen something called PIV(positive input ventilation)
Is anyone using such a system successfully?

We have MVHR but we are in a new build with good air tightness. We dry washing indoors with no condensation issues at all.

Assume you’ve checked for any underlying sources of damp on the house?

PIV will blow in fresh air and force out damp humid air, so you will need exit paths - the trickle vents should be sufficient, and you could swap these out to humidity controlled trickle vents. They are generally pretty effective systems.

The downside will be that incoming air will be colder so you may find your heating bill is higher, although it always seems to take a lot of energy to heat a damp house so it may balance out.

Where do you think the water is coming from?

Have you got a water meter?

How old is your house?

Have you sniffed under the floors?

Is it worse after rain?

Yep we have. We live in a very old cottage which has basically been sealed up by having new windows and a stove rather than open fire fitted.

We had terrible mould on walls with furniture up against them and me and dcs were suffering with bad asthma etc all winter.

We've had it in 2 years and it has got better although we're still very careful with not getting hanging washing etc.

We keep all the windows closed as the point is to positively pressure the house to force the moisture out through the walls. so opening the windows/ trickle vents will just let it all the imported air out there. Might be different for different designs/ sources of damp but that was my understanding of how it worked.

If you are in an old cottage then it will have a very low level of air tightness and the damp air will be forced out through the cracks in the building fabric, leaky windows etc.

Houses that are more airtight will need venting routes, hence trickle vents can be used.