Air purifiers, tested in a real room instead of a sealed chamber
Manufacturer figures come from a sealed test chamber. We measured in a normal bedroom with a door, a window and a person breathing in it, and the numbers moved a lot.
- Real-room clean air delivery averaged 61% of the rated figure
- The gap widened at low fan speeds, which is how most people run them
- Filter cost over three years exceeded purchase price on four of six units
Every air purifier is sold on a clean air delivery rate measured in a sealed chamber with no furniture, no door gaps and no occupants. We measured six units in a normal bedroom instead: 12 by 14 feet, a closed door with a standard undercut, one window, one person asleep.
Averaged across the six, measured clean air delivery in the real room came to 61 percent of the rated figure. The best unit reached 78 percent of its rating; the worst, 44.
Where the gap comes from
Three things. Air that leaks around the door and window is replaced by unfiltered air from the rest of the house. Furniture and bedding disrupt the circulation pattern the chamber test assumes. And particles settle on and re-suspend from surfaces, which a bare chamber does not have.
The gap widened at lower fan speeds. At the quietest setting — which is how anyone running one overnight actually uses it — measured delivery fell to between 28 and 41 percent of the rated maximum.
The rating is real and it is measured honestly. It just describes a room nobody lives in.— An indoor air quality engineer who reviewed our method
The cost that arrives later
Filters are the larger expense over any reasonable ownership period. On four of the six units, three years of manufacturer-recommended filter replacements cost more than the purchaser paid for the machine.
Two units accept generic filters at roughly a third of the price. Two use a cartridge with an authentication chip that disables the unit if an unrecognized filter is fitted.
- Real-room delivery: 61% of rated figure on average; range 44% to 78%
- At the quietest setting: 28% to 41% of rated maximum
- Filters: three years of replacements exceeded purchase price on four of six
- Two units reject third-party filters through an authentication chip
The practical advice: buy a unit rated for a room substantially larger than yours and run it on a low setting, which is quieter, cheaper to run and closes most of the real-world gap. Check filter prices before you buy, and check whether third-party filters work.
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