Test method
How we test air purifiers
The uses we score and the tests we run on every air purifier: PM2.5 clean-up in a smoggy bedroom, noise at night, power draw and sensor accuracy.
Every air purifier we review is run in a closed bedroom in Delhi-NCR during the October-November smog season, on the unit we bought or borrowed, and goes through the same tests below. That is what makes the results comparable: a clean-up time in minutes means the same room, the same starting pollution and the same finishing line for every purifier on the site.
Clean-up time is the number that matters most, because it shows the airflow a purifier really delivers, which is not always what its listed CADR suggests. Noise on the night setting and power draw come next, since most purifiers in Indian homes run all night and often on an inverter. Each test result in a review links back to the matching test on this page.
What we score
- Bedroom, overnight
- How quietly it runs on its lowest or Sleep setting, how well it dims its lights, and whether it keeps a closed bedroom's air clean through the night.
- Delhi winter smog
- How quickly it pulls PM2.5 down when outdoor AQI is in the 300s and 400s during the October-November stubble-burning weeks, and whether Auto mode keeps up.
- Large living room
- Whether it has enough airflow for a hall or living room above about 250 sq ft, judged from its clean-up time, its stated CADR and how hard it has to run.
- Small room or study
- How well it suits a kids' room, study or home office: footprint, noise at the desk or bedside, and clean-up in a room smaller than our standard bedroom.
The tests
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PM2.5 clean-up, 180 sq ft bedroom
In a closed 180 sq ft bedroom with a 9 ft ceiling, during Delhi-NCR's smog season, we burn incense to push PM2.5 to about 300 ug/m3, then time how long the purifier takes to bring it under 35 ug/m3, tracked on a handheld reference monitor.
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Noise on lowest or Sleep setting
We measure the sound level 1 metre from the purifier with the fan on its lowest speed, or its Sleep or night mode where it has one. This is the setting most people run overnight.
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Noise at top speed
We measure the sound level 1 metre from the purifier with the fan at its highest speed, the setting it uses to clear a smoggy room quickly or when Auto mode ramps up.
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Power draw at top speed
We measure power at the wall socket with the fan at top speed. It tells you what the purifier adds to your electricity bill and how much of an inverter's capacity it takes during a power cut.
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PM2.5 reading vs reference monitor
For purifiers that show a PM2.5 number on a display or in an app, we compare that number with a handheld reference monitor in the same room across the range of pollution we see in testing, and report the typical gap as a percentage.
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Colour light turns red at
For purifiers that show air quality only as a coloured light, we note the PM2.5 level on the handheld reference monitor at which the light turns red, so you know what the colours actually mean.