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I can buy a HEPA filter machine off the shelf. What I can't buy off the shelf is any other non-HEPA filter machine like you're describing. So while you might be

• Aurornis 2mo ago
  > What I can't buy off the shelf is any other non-HEPA filter machine like you're describing In locations with central air handlers, the filter in that handler already serves this purpose. That’s how my house is set up: Central handler has a high throughout MERV filter. Several rooms have additional HEPA purifiers. The parent comment also has a fallacious argument in assuming that the CADR is too low if a HEPA filter is present, but even the cheap HEPA purifiers I bought have sufficient CADR to cycle the room over and over. If you’re in a location with no central air handler (only mini splits or no air conditioning at all) and you have a giant space to cover and you have a constant exchange of air from the outside to overwhelm your filtration (must leave windows open, for example) then what the commenter above would apply. You would be better with a higher throughput, lower rated filter. For everyone else, it’s kind of a misplaced “well actually” take that has just enough information to feel truthy but misses the bigger facts.