HEPA purifiers: the CADR math
A HEPA filter is the most effective single intervention for indoor particulates. Sizing it correctly is the part most people get wrong.
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The Corsi-Rosenthal box-fan filter
A $50 box fan, four MERV-13 furnace filters, and twenty minutes of construction. Tests have measured clean air delivery rates of roughly 400 to 850 CFM.
HVAC MERV ratings: what your furnace filter actually does
MERV 8 catches dust. MERV 13 catches viruses. MERV 16 catches almost everything HEPA does. Most homes ship with MERV 6.
Recovery curves: how long until the air clears
After a source stops, each pollutant decays with its own characteristic shape. The math behind "the room should clear in about 20 minutes," and why real rooms don't always follow it.
Filtration approaches, compared
HEPA, MERV, Corsi-Rosenthal. Three filtration paths to the same goal. Cost, performance, deployability differ in different directions.
Reducing PM2.5 indoors: filtration plus source control
Two levers: stop making fine particles, and remove them when they appear. Start by asking whether the particles come from outside or from a source in the room.
