filters are tight (0.3μ) air strainers -
unecessatily restrictive, because their small openings are much
smaller than almost all particulate pollutants.
Pushing or pulling air through unnecessarily restrictive media creates
unnecessary noise and wastes energy.
Since troublesome particulates are easily removed by open,
free-flowing electret, HEPA filters are too expensive.
However, a HEPA filter can last a long time and be made to capture
- vacuum it using soft brush
- backward blast it with compressed air
(outdoors please, to avoid breathing allergens)