Review on Nordic Pure 20x20x4 MERV 12 2-pack Furnace Filters by Unm Weil

Works but I was surprised there were still fine dust particles in the room. I use it as a room air filter when I started smoking and saw smoke coming straight through the filter. Previously, it had a 3M filter rated Merv 10, which was not only able to filter all smoke, which also explains that other ratings for this filter are lower (e.g. FPR 7). This corresponds to Merv 8/9. , not 10. Also, the charcoal filter is much less effective than other filters I've used over the past 5 years and barely removes smoke odor even if I leave it running for up to 20 minutes after smoking. The 3M filter I had previously not only kept the smoke/aerosols out, but I was able to turn it off 5 minutes after smoking and there was no tobacco smell in the room.