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Home ventilation

Positive input ventilation (PIV) installation

Loft or wall units that gently push filtered air into the home to tackle condensation.

  • From £795 inc VAT per home
  • Free survey on the UK mainland
  • Airflow tested and recorded
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Positive input ventilation unit sitting on loft insulation

Positive input ventilation (PIV) is a single fan unit, usually in the loft, that pushes a gentle, continuous flow of filtered air into the home through a ceiling diffuser on the landing. The slight positive pressure pushes moist, stale air out through the normal leaks and vents, which is why PIV is one of the most cost-effective fixes for whole-house condensation.

How it works

Loft air is usually a little warmer and drier than outside air, and the unit filters it before it comes down into the house. Many units have a temperature sensor that reduces the flow or switches to a heater module on cold days, so the incoming air does not feel like a draught. Flats without a loft use a wall-mounted unit that draws air from outside through a cored hole.

PIV works well in houses and flats with general condensation on windows and cold walls. It does not replace extract fans: kitchens and bathrooms still need their own extract to remove steam at source. On survey we check the loft, the landing position and the existing fans, and we tell you if PIV is not the right answer.

Options we fit

Loft-mounted PIV

The most common option for houses with a loft. Usually fitted in half a day.

Heated PIV

A heater module tempers the incoming air in cold weather. Useful in homes where people feel draughts.

Wall-mounted PIV for flats

Draws air from outside through an outside wall. Suits flats and homes with no loft space.

PIV with fan upgrades

PIV plus humidity-controlled extract fans in the kitchen and bathroom for the most stubborn condensation.

Signs you need this

  • Streaming windows on most mornings in winter
  • Black mould on window reveals and in corners of bedrooms
  • Musty smell in wardrobes or behind furniture
  • The house feels stuffy and damp rather than cold
  • Washing dried indoors makes everything worse
  • You have no loft but still need whole-flat ventilation (wall unit)

Guide prices

Positive input ventilation (PIV) guide prices
WorkGuide price
Positive input ventilation (PIV) loft unit, supplied and fitted (per home)£795–£1,395 inc VAT
Wall-mounted PIV unit for a flat (core drilled through an outside wall) (per flat)£995–£1,695 inc VAT
Heater module or heated PIV unit (extra over a standard unit) (extra)£145–£295 inc VAT

Guide prices using West Midlands (our baseline) rates. Home prices include VAT at 20%; business prices exclude VAT. A guide price is not a quote: we confirm a fixed price in writing first. London is about 20% higher and the North East about 8% lower.

What happens, step by step

  1. Survey

    We check the loft or outside wall, the landing ceiling, the electrics and the existing extract fans.

  2. Fixed quote

    We recommend a unit and position, with or without a heater, and confirm the price in writing.

  3. Install

    Unit mounted in the loft or on the wall, diffuser fitted on the landing, fused spur wired.

  4. Set up

    Airflow set to suit the size of the home, heater and temperature settings checked.

  5. Hand over

    We show you how to change the filter and leave the manual and warranty details.

The rules that apply

England

In England, ventilation is covered by Part F of the Building Regulations and its guidance, Approved Document F (2021 edition). For homes, it sets minimum extract rates such as 15 litres a second for a bathroom and 30 or 60 for a kitchen, and expects mechanical systems to be airflow-tested.

Wales

Wales has its own Part F ventilation guidance, published by the Welsh Government, and work is checked by building control. We design to the Welsh rates and commission mechanical systems so the results can be recorded.

Scotland

In Scotland, ventilation is covered by the Building (Scotland) Regulations and section 3 of the Technical Handbooks, and most building work needs a building warrant first. We work to the Scottish ventilation standards and record the airflow achieved.

Northern Ireland

In Northern Ireland, ventilation is covered by the Building Regulations (Northern Ireland) and Technical Booklet K. We design to the Northern Ireland guidance and measure the airflow achieved.

Questions people ask

How much does PIV cost to install?

A loft-mounted PIV unit usually costs £795 to £1,395 including VAT supplied and fitted, and £995 to £1,695 for a wall-mounted unit in a flat. A heater module adds around £145 to £295.

Does PIV really stop condensation?

PIV reduces condensation in most homes because it dilutes moist air and keeps it moving, but it works best alongside working extract fans in the kitchen and bathroom. Leaks, rising damp or a cold bridge need fixing separately.

How much does PIV cost to run?

A standard PIV unit uses very little electricity, comparable to a low-energy light bulb on normal speed. A heated unit costs more in cold spells because the heater switches on when loft air is cold.

Will PIV make my house cold?

Most units temper or reduce the flow when the incoming air is cold, and a heated unit warms it. Placed correctly on the landing, the air spreads gently rather than blowing on anyone.

Can PIV be fitted in a flat?

Yes. Flats without loft space use a wall-mounted PIV unit that draws air from outside through an outside wall.

How long does PIV installation take?

A loft unit is normally fitted in two to four hours, including the diffuser and electrical connection.

Related services

Modern bathroom with walk-in shower and wall extractor fan

Extractor fan installation

Bathroom, kitchen and utility fans sized to the Part F rates, ducted outside and tested.

From £175 inc VAT per fan

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