Positive Input Ventilation (PIV) is a type of mechanical ventilation system that introduces fresh air into a building, typically a residential property, to improve indoor air quality and reduce condensation and associated problems.

PIV systems work by drawing air from outside the building into a central unit, typically located in the loft or roof space. The air is filtered and heated, if necessary, before being introduced into the living areas of the property through a series of ceiling-mounted vents. This creates a positive pressure in the property, which forces stale and damp air out through natural ventilation points such as windows and doors.

The benefits of PIV systems include:

1. Improved indoor air quality: PIV systems help to dilute and remove pollutants and allergens, such as dust, pollen, and mould spores, from the indoor air.

2. Reduced condensation and mould growth: PIV systems can help to reduce excess moisture in the air, which can lead to condensation and mould growth.

3. Enhanced thermal comfort: PIV systems can help to distribute warm air throughout the property, creating a more consistent temperature and reducing cold spots.

4. Energy efficiency: PIV systems can help to reduce heating costs by distributing warm air more efficiently and reducing the need for artificial ventilation.

PIV systems are generally considered to be a cost-effective and energy-efficient solution to indoor air quality and ventilation issues in residential properties. They are relatively easy to install and maintain, and can be fitted into most types of residential properties.