What room size should I match my purifier to?

Manufacturer square-footage claims are usually based on a single air change per hour, which is weak for allergies or smoke. A common rule among reviewers is to pick a unit rated for roughly double your room size so it can deliver four to five air changes per hour on a mid fan speed. Levoit's Vital and Core lines and the Blueair 211i Max are the most frequently cited for covering larger spaces in the candidate pool.