Positive Input Ventilation (PIV)

PIV units are suitable for most UK house types with a loft space. They connect to a single ceiling diffuser, typically in a hallway, so there's no complex ductwork run to every room. Installation is straightforward and most units can be fitted in a day. Running costs are low: most PIV units consume 15–30 watts continuously, which works out to roughly £20–£50 per year at typical UK electricity rates. For colder climates or less well-insulated homes, heated PIV units, such as the Vent-Axia PoziDry Pro with Heater or the Elta PIV ONE PLUS+, warm the incoming air before it enters the home, making the system effective and comfortable year-round.

Our PIV range includes loft and wall mounted units from Vent-Axia and Elta, ranging from the compact PoziDry Compact Pro (suitable for smaller properties) to the PoziDry Pro Multi Storey for larger homes. If you're not sure which model is right for your property, read our PIV guide or see our Vent-Axia vs Elta comparison to help narrow it down.

Frequently asked questions

What is a positive input ventilation (PIV) unit?

A PIV unit is a whole-house ventilation system that sits in the loft and continuously supplies filtered fresh air into the home via a ceiling diffuser, usually in the hallway. The gentle positive pressure pushes stale, humid air out through gaps and vents in the building fabric, reducing condensation, mould, and indoor pollutants without requiring a full MVHR installation.

Do I need a PIV unit with a heater?

In most UK homes, yes, a heater is recommended. Loft temperatures can drop significantly in winter, and without a heater the system would introduce cold air into the living space. Units with integral heaters gently warm the supply air to a comfortable temperature before distributing it, making them far more effective year-round. Our best-selling models include the Vent-Axia PoziDry Pro with Heater and the Elta PIV ONE PLUS+.

Is a PIV system easy to install?

PIV units are among the simpler whole-house ventilation systems to install, because they don't require ductwork runs to every room. The unit is mounted in the loft, connected to a single ceiling diffuser in the hallway below, and wired to a standard fused spur. Most installations are completed in a day.

What size property does a PIV unit suit?

Loft mounted PIV units are designed for standard residential properties, typically houses with a loft space. For flats and properties without a loft, a wall mounted PIV unit such as the Elta SANO IPIV WALL H or the Vent-Axia PoziDry Compact Pro fits on an external wall instead. Alternatively, consider a continuous mechanical extract (MEV) or MVHR system.

How much does it cost to run a PIV unit?

PIV units are designed to be low-energy, typically consuming 15–30 watts in standard operation, comparable to a low-energy light bulb. Annual running costs are generally in the range of £20–£50 depending on usage and heating requirements.