What is the Difference between PIV and MEV

Whole house ventilation systems can be the most effective way of improving the indoor air quality in your home.  By improving the airflow in every room of your property, both systems will reduce humidity which will stop condensation and prevent damp and mould from developing.

If you are considering an upgrade to a whole house ventilation solution, it is important to speak to a ventilation expert who can advise you about what is best for you.  In this guide, we cover the key differences between Positive Input Ventilation (PIV) and Mechanical Extract Ventilation (MEV) systems.

What is Positive Input Ventilation {PIV)

Positive Input Ventilation systems use a central unit – usually mounted in the loft of a property – to draw fresh air from outdoors into the building.  PIV systems incorporate filters into the air intakes to maintain good air quality and prevent allergens such as pollen and particulate air pollution from being drawn into the property.

The incoming air creates a positive air pressure inside the building, and the stale air is then allowed to escape through the natural ventilation in your home taking moisture and other indoor air pollution such as radon and volatile organic compounds from cleaning product with it.

Positive Input Ventilation Systems distribute fresh air throughout your home which helps to even out temperatures and prevent rooms from getting stuffy in hot weather. Some systems incorporate a heater which will warm the incoming air and help to keep your home warmer in winter.

The main advantage of PIV systems is that by controlling humidity levels throughout your home, they are very effective at preventing condensation.  While extractor fans in your bathroom and kitchen can remove large volumes of steam from cooking and bathing, other sources of moisture in the air throughout your home such as drying clothes and even breathing are less effective.

The improved inward air flow from PIV systems displaces moisture rich air which then prevents condensation from forming throughout your home – even in less used rooms and areas where mould and mildew can often be a problem such as behind furniture.

They are highly efficient in operation and can cost less than £10 per year to run without a heater, and from £70 annually for systems with a heater. 

PIV systems can be installed in an existing property with minimal disruption and are a popular option for people who want to improve their air quality and prevent condensation. PIV systems are highly recommended for residents in areas with high radon levels as they are effective at preventing a build-up of this radioactive gas.

What is Mechanical Extract Ventilation (MEV)

Mechanical Extract Ventilation (MEV) works in the same way as a conventional extractor fan system.  Rather than displacing the air in your home by actively drawing in fresh air from outside, MEV systems pull air from wet rooms such as bathrooms and the kitchen in your home and pump it out of the building.  Fresh air is then drawn in to replace the stale air that has been removed.

Like PIV systems, MEV systems have a central unit which draws air in from around the house and then disperses it outside.  MEV Systems run continuously but are very efficient and quiet with the annual running costs of a typical system starting from less than £20 in a home.

Due to their design and the way they work, MEV systems are normally installed as part of a major renovation or a new build rather than being retrofitted into an existing property.

What is Mechanical Ventilation with Heat Recovery (MVHR)

Another form of ventilation is mechanical ventilation with Heat Recovery (MVHR) which use heat exchangers recover the heat from the outgoing air and use it to heat air that is being drawn in to replace it and are highly efficient, retaining more than 85% of the heat energy.  Systems are highly efficient in use with an annual running cost of a little more than £40 in a flat and approximately £59 in a house.

Like MEV systems, whole house MVHR systems are normally only installed as part of a wider renovation project or as part of a new build.

Find out more

If you are considering a whole house ventilation system to improve your indoor air quality, speak to one of our local ventilation specialists.  Simply enter your postcode below to find a ventilation expert in your area.  They can visit your property to carry out a free home survey and advise you about the best system for your needs.