How the math works
ClariSelect mathClean air needed (CFM) = room volume in cubic feet × air changes per hour ÷ 60. A 15 × 13 ft room with an 8 ft ceiling at 4.8 changes per hour needs about 125 CFM.
LimitsCADR (clean air delivery rate) is the most comparable number; makers who publish it usually give smoke, dust and pollen figures, and smoke is the hardest. Room ratings quoted 'in one hour' are a single air change and are left out here.
Questions
What CADR do I need for a bedroom?
For a typical 12 × 12 ft bedroom with an 8 ft ceiling, about 92 CFM at 4.8 air changes per hour.
Is a bigger air purifier better?
A unit sized above your room can run on a lower, quieter setting and still clean the air, which is usually the better choice for a bedroom.