Why MEV & dMEV are superior to PIV

Many businesses, institutions, and private homeowners are examining how they can improve ventilation. Badly ventilated spaces can cause or contribute to  health problems, including asthma, allergies, and a weakened immune system. Before investing in ventilation, it’s important to consider how different systems work and what the best option is for your needs. Here we explore 

What is PIV?

Positive input ventilation (PIV) is a method of ventilation that has been around for many years. Often used to negate condensation and dampness, it pumps and circulates air from the outside into the house and pushes stale air out of gaps and cracks in the fabric of the building. It works as a whole house ventilation system, creating fresh and healthy living environments by supplying continuous fresh, filtered air into a property. By introducing the circulated air system, PIV was thought to help to reduce issues such as condensation and mould, creating a safer and healthier environment. 

How does a PIV unit work?

PIV is typically introduced into a home or building in the form of a ceiling mounted unit installed in a loft or roof vent. The unit will have a fan inside that draws air in and pumps it through the house. The air that travels through the building creates a shift in pressure that pushes contaminants and stale air out of any small gaps in the walls. Rather than removing all of the stale air, PIV works to dilute stale air with fresh air. 

Why is PIV considered ineffective?

PIV systems were developed in the 1970s and are now considered outdated and much less efficient than modern ventilation methods. Simply put, PIV has been surpassed by newer systems, which deliver much better results. 

One of the most consistent criticisms of PIV is that it needs proper ventilation leakage opportunities in a building to work properly. Whilst this isn’t an issue in older properties, new builds are designed to be airtight, limiting the potential for ventilation leakage. As well as this, PIV draws both hot and cold air through a house, and even with small amounts of air travel this can significantly impact the temperature and overall comfort levels in the home. 

PIV systems can also be combined with heaters or extractor fans to keep a house both warm and ventilated, but critics argue that this simply undermines the otherwise low energy qualities of the PIV. As well as being less energy efficient, running heaters and/or fans alongside the PIV would likely increase the running costs significantly. Some PIV systems shut off at 27 degrees, from which point the building goes completely unventilated. 

What is MEV and dMEV?

Mechanical Extract Ventilation (MEV) and Decentralised Mechanical Ventilation (dMEV) are ventilation solutions that are better suited to contemporary housing. Unlike PIV, MEV and dMEV systems do not rely on ventilation leaking spots making them a more efficient cost effective solution that can stop the onset of damp and mould without sacrificing a building’s insulatory qualities. 

• Mechanical Extract Ventilation (MEV): Mounted in a loft or cupboard, MEV is a central unit that extracts polluted air from wet rooms in a building. The central unit connects all of the extractor vents in the property together. 
• Decentralised Mechanical Ventilation (dMEV): With small, continuously running fans, dMEV systems are installed in each room with ducting that links directly to the outside. dMEVs offer a quiet, energy-efficient solution that costs less to run than other systems. 

Both MEV and dMEV systems work by extracting stale, moist air from rooms in the property that are most likely to be wet- such as bathrooms, en-suites and kitchens. The air is continuously extracted from the inside of the property and released via ducting to the outside.