One of the more common requests we get is to do a cross between different filter test methods. For years it was a 52.1 to 52.2 cross, then when Europe adopted EN779 charts crossing those two came about now with the adoption and publication of ISO 16890 we are being asked to create a comparison ASHRAE 52.2 Chart and the ISO Chart. For filter professionals (or maybe better said as filter geeks) like us is that this can not be done while respecting the two standards because they measure two very different things, but we have developed our own close approximation of the two.
Before we dive right in to creating a comparison/cross between the MERV Chart and the ISO 16890 table it is first important to understand what the two standards are measureing and reporting. We'll skip the detail and in-depth analysis here as you can get that in our free eBook Comparing ISO 16890 and ASHRAE 52.2 MERV which you can download by following this link:
As we can see in the MERV Chart here, the standard measures the percentage of particles captured at specific, narrow particle size ranges. Thes ranges (E1, E2, and E3 are further divided into 4 sub-ranges which make up the composite for the entire "E" rage) There is no mention of how these particle sizes correspond with the distribution of particles in the air, and more worrisome is that these limits were not determined scientifically or with regard to real-world air quality it is in some respect random classifications.
In contrast, ISO 16890 is tested against the particle capture of all particles in a range based on the particle size distribution of Particulate Matter (PM) - this distribution curve has undergone intense scrutiny and has been peer reviewed an almost countless number of times. By using this as the metric that detemines filter efficiency it is more straightforward to how clean the air is getting after air passes through the filter.
The rating table for the ISO standard then is broken down in 4 different broad catagories, very similar to how the industry, regulators, and advocate groups already discusses air quality, they are ePM1 (the smallest and most harmful particles) ePM2.5 (used extensivley by the WHO and EPA) ePM10 (also used by the WHO and EPA) and lastely ePM-Coarse (for very light-duty or pre-filtration applications) The smaller the ePM size (1, 2.5 or 10) the more particles the filter will remove: i.e. a filter rated ePM1-50% removes significantly more particles than a filter rated ePM2.5-50% There are a lot more efficiency options here when compared to the ASHRAE 52.2 chart, but most filter companies do not offer an option in each of the rated catagories, much like must filter manufacturers do not offer filters in all 16 MERV.
Again, with how different these standards are, there is no way to say that if a filter that is assigned a certain MERV will be assigned to a certion ISO 16890 class - the standards are just too different. That being said there is a demand for some kind of recommendation to be made to make the transition from one standard to the other so here is our subjective approximation:
As always, if you have additional questions or comments, please contact us. We're here to help!