A purifier that is too small for the room is the most common and most expensive mistake buyers make. It runs flat out, sounds like a jet, and still never catches up. Here are five sizing errors to avoid.
1. Trusting the headline room rating Manufacturers often rate a purifier for a large room based on a single air change per hour. That is enough to make a label look impressive but not enough to actually clean the air. Demand at least four air changes per hour.
2. Ignoring CADR Clean Air Delivery Rate, or CADR, is the honest number. It tells you how much clean air the unit delivers per minute. Match CADR to your room: a rough rule is CADR (in cubic feet per minute) should be at least two-thirds of your room's square footage for solid performance.
3. Forgetting ceiling height Room ratings assume an 8-foot ceiling. A vaulted or 10-foot ceiling adds a lot of air volume, so you need a bigger unit than the square footage alone suggests.
4. Buying one unit for a whole floor Purifiers clean the room they are in. Open-plan spaces and multiple rooms need either a larger unit or several smaller ones, not one box doing impossible work.
5. Sizing to run on max Buy a purifier whose mid setting handles your room. Running constantly on high is loud, wears the motor, and discourages you from leaving it on. Headroom means quiet, comfortable operation.
Get sizing right and a modest purifier outperforms an oversized one strangled in a too-big room.