Ventilation does one job
Ventilation replaces moist indoor air with drier outdoor air. It does not warm surfaces and it does not stop water entering the fabric of a building, so it is a genuine part of controlling condensation and no use at all against a leaking gutter. Knowing which problem you have is therefore the first question, not the choice of equipment.
Extract ventilation: remove moisture at source
An extract fan in a kitchen, bathroom or utility room removes water vapour where it is produced, before it spreads through the house. It works well when the fan is adequately sized, ducted by the shortest sensible route with as few bends as possible, terminated properly outside, and — most importantly — actually run for long enough. A fan switched off with the light, in a bathroom still full of steam, has done very little.
Why extract fans disappoint
The usual reasons are mundane: flexible ducting crushed in a loft, a terminal with a stuck flap or a bird's nest behind it, a fan rated for a cloakroom serving a family bathroom, ducting so long that the fan cannot shift air through it, and no replacement air able to enter the room because the door seals tightly and there are no trickle vents. The fan is often fine; the installation is not.
PIV: dilute moisture across the whole dwelling
Positive input ventilation places a unit, typically in the loft, which gently introduces filtered air into the house at a low rate, usually from a central hallway. Rather than extracting at source it dilutes the moist indoor air and encourages it out through the building's existing leakage. It suits properties with a general humidity problem across several rooms and a reasonably open internal layout.
Where PIV is not the answer
It is not a substitute for extract in a room producing large amounts of moisture, it cannot warm a cold surface, and in a very cold dwelling it can make rooms feel draughty if commissioned carelessly. Nor will it do anything about penetrating damp, rising damp or a plumbing leak — and an assessment that recommends a unit without measuring the wall temperatures has skipped the most likely cause.
What we do, and what we do not
We assess conditions: humidity, dew point, surface temperatures, the existing provision and how the property is used, and we set out in writing what is needed — including where mechanical extract or a whole-dwelling system is genuinely the right answer. We do not supply or install ventilation equipment, so nothing in our recommendation depends on you buying a unit from us.
Limitations of general guidance
This article is general guidance. It cannot confirm the cause of dampness in a specific property. Recommendations should follow an inspection of the building, its external environment and its internal conditions.
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