Air Purifiers, Tested: CADR Numbers vs. Real Rooms

Air purifier marketing runs on a single number: CADR, or Clean Air Delivery Rate. It is a legitimate measurement — in a sealed, standardized test chamber. The problem is that nobody lives in a sealed test chamber. We wanted to know how these machines behave in a home with pets, cooking, open doors and pollen season, so we ran six units through an open-plan apartment for four weeks.

Where CADR Tells the Truth — and Where It Doesn't

CADR is excellent for comparing airflow at a given fan speed and filter type. It is unhelpful for guessing how many air changes per hour you actually get in a real room, because real rooms leak, have furniture, and are often larger than the "covered area" figure quoted on the box. A purifier rated for 1,300 sq ft might cycle a 300 sq ft bedroom five times an hour and the advertised open floor plan barely once.

The Six Units, Side by Side

The loudest unit was also the cheapest to maintain, which sums up the trade-off neatly: motor efficiency and filter cost usually move in opposite directions.

What Actually Moved the Needle

• Filter cost per year matters more than sticker price — the cheapest unit was the most expensive to own over three years.
• Auto mode is worth paying for; a sensor that ramps the fan up during cooking keeps electricity use sane.
• Placement beat horsepower: a mid-range unit near the room's air path outperformed a large one stuck behind a sofa.