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What is Positive Ventilation - PIV

Positive Pressure Ventilation

Positive Input Ventilation (PIV) systems create fresh and healthy living environments by supplying fresh, filtered air into a property at a continuous rate throughout a property and is our most popular method of whole house ventilation in existing houses or landlord lets.

PIV units help to eliminate surface condensation, prevent mould growth and reduce house dust mite populations. And are also reported to offer a wide range of energy saving and health benefits.

Loft mounted PIV units use free solar energy generated from the natural solar gain in lofts which, in turn, maximises comfort and contributes to annual energy savings.

Features of Positive Input Ventilation Systems

  • Highly effective at reducing condensation and mould
  • Improved indoor air quality (IAQ)
  • Energy efficient as low as 1p to day to run
  • Unobtrusive and whisper quiet
  • Selectable air capacities
  • Complete with ceiling diffuser, flexible duct and worm drive clips
  • Standard 5-year guarantee
  • maintenance free G4 filter
  • IPX2 rated

Why Do We Need a Positive Ventilation System (PIV)?

Over the last decade there has been increasing demand on builders, architects and government legislation to increase the thermal efficiency of our homes making them draught free and well insulated. This has caused poorer air quality that can significantly increase the effects of asthma and other respiratory problems, health problems, condensation, mould, dust mites, unpleasant smells and build-up of toxic gases.

Watch Pozidry Positive Ventilation Videos.

PIV Models

There are two models available:

Loft Mounted Unit – The units continually introduce a subtle filtered air supply from the trapped heat and fresh air from your roof void via a ceiling mounted diffuser normally in your hallway and redistributes the heat trapped at ceiling level. The moist, stale air is then forced out of the property through natural ventilation points (window trickle vents).

Wall Mounted Unit – Is ideal for apartments and houses without a loft that takes air from outside and supplies the air to a chosen area in the house via 100mm ducting.


The loft mounted unit has a 5-year maintenance free filter and the wall mounted unit requires the filter cleaned annually.

Landlords and Social Housing

Keep your tenants happy and reduce your on-going maintenance costs with the installation of a positive ventilation system (PIV) that has been successfully used to eliminate surface condensation, prevent mould growth and reduce house dust mite populations in social housing around the UK and ROI.

Data Log

Ideal for social housing, this function will display total runtime of system, time spent in trickle speed, time spent in normal speed, approximate energy consumption of the fan and approximate energy consumption of the heater unit. This data is non-resettable.

Running Costs

PIV won't cost tenants the earth - as little as a penny a day to run!

Please note that the winter heater models can use between 300 and 500 watts depending on the model.

New Airtight Build Houses 

New airtight homes are recommended to install a heat recovery ventilation system (MVHR) and not a positive ventilation unit (PIV).

A positive ventilation unit works by pressurising the property and the contaminated air is pushed out through natural paths in the dwelling's facade or window trickle vents.

If the property is built at or below 3 m3/hr/m2 air losses at a pressure of 50 Pa there would not be enough air leakage for the unit to work effectively. 

Size of Properties

The loft mounted unit is suitable for houses up to 1500 square foot floor area (150m2).

The wall mounted unit is suitable for apartments of up to 1000 square foot floor area (100m2).

The use of multiple units is possible.

Fire Prevention

If you are installing into a multi-story building, we can supply a Fire Damper model supplied with a relay to fire alarm cut off and intumescent fire protective ducting.


A PIV unit is one of the most cost-effective whole house ventilation solutions for existing homes as it requires very limited ducting and few penetrations in the external façade of the building.

The loft mounted unit only requires a 200mm round opening in the hallway for the diffuser and you simply install the unit in the loft and connect the unit to the provided ducting and switch on.

The wall mounted unit will need a 100mm diameter hole drilled through the wall and then simply fit the unit to the wall and duct to the preferred location of the diffuser and switch on.

Power supply is 3 amps for the standard model and 13 amps for the heater version.

Speed Control and Sensors

Both the loft and wall unit have simple to adjust variable speed control to adjust the speed of the unit in relation to the size of property.

A sensor monitors the temperature in the loft, automatically adjusting the air volume when necessary.

‘Trickle’ speed is automatically selected when the ambient loft temperature is less than 18°C.

‘Normal’ is automatically selected when the ambient loft temperature is between 18 and 27°C.

If the ambient loft temperature exceeds 27°C, the unit will automatically switch to standby (no airflow).


An electrical heater is available and can be installed either to the fan unit or as with the loft unit directly to the diffuser spigot.

The heater element is activated by default when the loft air temperature is below 10°C; the system will then work to maintain an input air temperature of 10°C. This temperature threshold can be adjusted between 5°C and 20°C during commissioning.

Categories: PIV Positive Ventilation General Information


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