MVHR systems are great but they need the right filters and the right maintenance to do their job well. I draw your attention to a useful article published by Scottish ventilation consultancy and design service, Paul Heat Recovery. Filters remove various pollutants like dust, pollen, smoke and other particulates, making sure the air circulated inside buildings is clean and fresh. The most basic function of a MVHR filter is to protect the system’s heat exchanger. But better filters will deliver much cleaner air and a healthier indoor environment. The article emphasises the need for regular filter maintenance and replacement and describes the different filter grades (G3, G4, F7) and the specific purification requirements they meet.
Source: Pauls Heat Recovery
New Zealand homes are typically exposed to particulates from wood fire smoke, pine pollen and car exhaust, making air filtration essential for a healthy indoor environment. The right grade of MVHR filter can effectively remove these contaminants from the air, protecting people from potential health issues caused by poor air quality. By exchanging damp, stale air with the continuous supply of fresh, filtered air, MVHR systems also help to prevent condensation and mould.
We recommend that Passive House buildings have F7 filters installed in their MVHR systems. This level of filtration lowers pollen (>85% of 10 micron particles) as well as dust. The more common G7 filters are really only designed to keep the MVHR ductwork clean and thereby protect the heat exchanger. For people sensitive to pollen—and hayfever is rampant in this country—F7 filters will remove almost all the pollen. They also remove fine particulate matter, and that matters a lot for protecting human health, as we discuss here.
We’ve been asked what the US MERV filter ratings are equivalent to. F7 is approximately MERV13 or ISO PM2.5 > 65% capture. Air filtration manufacturer Camfil has published a very useful conversions chart. It compares the relevant ASHRAE standard to ISO and EN standards.
Source: Camfil