Positive Input Ventilation (PIV) gently pushes filtered fresh air into your home from a single loft-mounted unit. It costs £400–£900 fitted, uses about £15 of electricity a year, and dramatically reduces condensation, mould and dust mites in homes that can't justify MVHR.
How PIV works
A small low-wattage fan in the loft draws cool, filtered air from outside and pushes it into the hallway through a ceiling diffuser. The slight positive pressure forces damp stale air out through trickle vents, extract fans and natural leakage paths.
When PIV is the right choice
PIV shines in older UK housing stock; pre-1990s flats, terraced houses with persistent condensation, and tenanted properties where ducting MVHR isn't practical. It's the cheapest mechanical ventilation upgrade by a wide margin.
PIV vs MVHR; which should you choose?
PIV is one-quarter the cost of MVHR but recovers no heat. In a leaky older home that's irrelevant; you'd lose the heat anyway. In a modern airtight build, MVHR pays back the difference within 5–7 years.
Best UK PIV units
Nuaire Drimaster Eco, EnviroVent ATMOS and Vent-Axia Pozidry are the three benchmark units. All include filtered air, summer bypass, and 5-year warranties.
PIV cost vs alternatives
| PIV unit + install | £400 – £900 |
| Annual running cost | £10 – £25 |
| Equivalent MVHR retrofit | £5,000 – £6,500 |
| Equivalent dehumidifier (energy) | £180 – £400/yr |
See what installers in your area would actually charge.
Get matched quotesFrequently asked questions
Does PIV cure damp?+
Yes for condensation-related damp and mould. It doesn't fix penetrating damp or rising damp; those need fabric repairs first.
Will PIV make my house cold?+
Modern PIV units include a heater element and temperature limiter; incoming air is tempered to 10°C minimum, so you won't feel cold drafts.
How long does PIV installation take?+
Half a day. A loft drop, ceiling diffuser, fused spur and commissioning is typically done in 3–4 hours.