My homeowner uses MERV 4 filters which usually work. But they didn't get the smell of smoke out of the air — I live in the Bay Area, where annual wildfires raise the PM2.5 air quality index to 167. It might smell like a good BBQ at first, but then it gets stale after a while, especially when I start to sneeze. Replacing this MERV 13 filter quickly eliminated the irritants and didn't appear to be a problem for my HVAC unit.
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