Summary: I got the MERV 12 20x20x4 filter. It looks like it can do the job, but does not seem to remove any particulate matter from the air. In other words, it doesn't filter/clean the air at PM.5 and only marginally at PM2.5. Nearly any filter that is better than a dust filter will outperform this Nordic Pure filter. Details: I have 8 air cleaners in my home, including two BlueAir605 and Honewell HEPA and measure them regularly with a Dylos DC1700 particle counter. Two air cleaners that I use as supplemental are 20" box fans with 20x20x1 furnace filters. It's fire season with outdoor AQI at 63, but that doesn't really matter for this test. My wife burned her breakfast, so I took the "Nordic Pure 20x20x4 MERV 12 Pleated AC Furnace Air Filters 2 Pack" out of their box and coupled it with the fan. The ambient measurement in the room for .5PM was 27,000 particles in approximately .01 cubic foot of sampled air, which is about right. You can smell the burnt food. Also, on a day where the outdoor AQI is 150, this measurement can be similar to this reading (25,000 - 30,000). When I hold it to the Nordic Pure MERV 12, the .5PM measurement is essentially the same. In other words, it's not filtering anything at PM.5. I've never seen this before! Ever!! Especially for a MERV 12 filter!!! A MERV 8 can do much better than this!!!! I've done this experiment many times over the years. I have two filters next to me. They are not Nordic Pure, but a different brand: MERV 11 and MERV 14. Both the MERV 11 and MERV 14 showed commensurate reductions that were inline with their MERV rating, 24,000 and 21,000 respectively. That's about right for a smoky room. It won't go much lower in this situation because the air mixes so much, even if you hold it at zero inches. I later tested it against my HEPA filter and the reading went from 300 to nearly zero, so the meter is functioning correctly. If you have questions on the validity of this type of filter, please watch youtube video, Michigan Medicine, Dr. Jeffrey E. Terrell, director of the Michigan Sinus Center, "Build a do-it-yourself air purifier for about $25." On the slightly positive side, when the burnt smell was heavy, I did see a reduction in PM2.5 from 900 down to maybe 600 particles per .01 cubic foot of sampled air. Not great either, but at least it's doing something. I've seen MERV 8 filters perform much better than this. To be fair, I should mention that the measure of MERV 12 is more closely tied to PM2.5. It needs to show a reduction of PM1.0-3.0 80%-89.9%, 3.0-10.0 90% or greater. I'm measuring PM.5 because that's what we care about with wildfire smoke, the smaller particles; however, I will say that ALL of the other brands that I have worked with do a GREAT job with the smaller particles (PM.5), even one of a much lower MERV rating. This furnace filter should perform very well, especially because it is 4" thick, but it doesn't. The smoke is gone, and I did the experiments over again. The Nordic MERV12 didn't show any improvement in PM2.5 or PM.5. Ambient counts are 287 and 17 respectively. The other brand, MERV11 and MERV14, despite being only 1" thick, showed substantial improvement in both measurements. Even the MERV 11 filter cut PM2.5 counts in half. To give the 4" Nordic an edge, I sealed the areas between the fan and the filter; no improvement. Tried positioning the meter in different ways, no improvement. I've used another brand of 4" MERV 8 filter that worked really well; it was 20x24x4. That was the only size I could get, and it was 4" taller than the fan. It didn't matter. Worked great. I'm surprised that this Nordic Pure filter doesn't do much. Returning. Everything is sold out due to smoke and COVID, so I have few other options. About me: I have a technical background and own a Dylos DC1700 particle counter, which is the correct tool for measuring filter performance. Since 2016 I have been active in improving air quality in my house and have gone over to a few dozen different indoor environments during wildfire season to help my friends and a local school reduce their wildfire smoke exposure. My friend is in the HVAC business and manages a team that is responsible for a very large tech campus here in silicon valley. He is union trained with 20+ years of experience in commercial HVAC. I vet my work with him and we talk for hours on end about air filtration while using this particle counter. I enjoy working with my particle counter and use it sometimes every hour during California smoke season. I have fun adding air cleaners and filtration and tweaking everything to get low particle counts (clean air). The response of the meter is nearly immediate when you hold it in front of the air cleaner, so it can really show you what's going on by doing little experiments.
