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