Ventilation is a system.
Homes produce moisture through cooking, bathing, washing and everyday occupancy. The government’s existing-home ventilation guide describes ventilation as the exchange of fresh outside air with stale, moist indoor air.
PIV may help some homes by introducing filtered air, but it does not fix rainwater entry, plumbing leaks, damaged masonry or every mould problem. It also needs a suitable installation, clear air paths and ongoing use.
Damp first
Rule out leaks, penetrating damp and persistently wet building fabric before treating humidity alone.
Air movement
Consider extract fans, trickle vents, door undercuts and whether air can move through the home.
Property fit
Review loft conditions, filters, controls, combustion appliances and manufacturer instructions.
Use the right standard.
For work in England, ventilation requirements and technical guidance sit within Part F of the Building Regulations. Existing homes, new work and local circumstances can differ, so installation should follow the relevant guidance and manufacturer instructions.
See Approved Document F on GOV.UK →What a PIV assessment should answer.
PIV is more plausible where the main issue is moisture-laden indoor air and the home has a suitable place for the unit and a workable route for air to move out. It is a poor substitute for repairing a leak, restoring a failed extractor or dealing with a cold bridge.
- Where will the unit draw or introduce air, and is the loft or other location suitable?
- Can moist air leave through working extract and background ventilation?
- Will the system affect combustion appliances, noise, draughts or comfort?
- Who will replace filters, check operation and deal with alarms or faults?
Useful information before installation.
- Humidity, temperature and the rooms where condensation or mould appears.
- Existing extract fans, trickle vents, door undercuts and likely air paths.
- Loft condition, insulation, access, electrical supply and proposed discharge route.
- Combustion appliances and any need for a qualified specialist check.
- What will be monitored after commissioning and what remains outside the scope.
Official ventilation guidance.
GOV.UK: existing home ventilation guide explains moisture, background vents and extractor maintenance. GOV.UK: Approved Document F sets out the building-regulations guidance for ventilation in England. Follow the installed system’s manufacturer instructions as well.
PIV in context.
What does PIV do?
Positive input ventilation introduces filtered air at a controlled rate to encourage air movement through a home. It is one ventilation option, not a universal damp treatment.
Will PIV cure every mould problem?
No. It cannot repair a leak, remove a bridge or replace a defective extractor. The property and moisture source need to be assessed first.
What should be checked before PIV is fitted?
Check existing extraction, background ventilation, air transfer routes, loft suitability, combustion appliances and the property’s moisture load.