Calculators
Air equipment calculators: inputs you already have, one formula, one answer, with the formula printed so the number can be checked.
Each calculator takes numbers a homeowner already has, applies one formula, and returns one answer. The formula is printed on the page so the result can be checked by hand.
Air purifier room size calculator: the smoke CADR a room needs on AHAM's two-thirds rule, and the air changes per hour a given purifier delivers
AHAM's rule: smoke CADR at least two-thirds of the room's square feet at an 8 ft ceiling (room size = 1.55 x CADR); ACH = CADR x 60 / volume. 180 sq ft: 120 cfm.