What size air purifier do you need for your room?

For allergy relief: 20 × 2.7 × 4 ≈ 215 m³/h. In practice, look at models marketed for 40+ m², and check the noise at night speed — for bedrooms the sweet spot is a unit big enough to clean the room on its quiet setting (under 30 dB), rather than a small one screaming at maximum.

For airborne allergens — pollen, pet dander, dust — yes, measurably, provided the CADR fits the room and it runs continuously during the season. What they can’t do: allergens already settled in carpets and bedding (that’s vacuuming and hot washing), and dust mites living in mattresses. The winning combo for allergic sleepers: purifier running all night, anti-mite covers, and the bedroom door closed.

A lot. True HEPA H13 captures 99.95% of particles at the hardest-to-catch size (0.3 microns); "HEPA-type" or "HEPA-like" filters have no certified standard and can stop at 90-95% or less — a 10-100× difference in what gets through. For smoke and fine urban particulate (PM2.5), also look for a substantial activated-carbon stage: HEPA alone doesn’t touch odours and gases.

During pollen season or pollution peaks, yes — particles re-enter constantly, and clean air lasts less than an hour once the unit stops. Consumption is modest: 20-50 W at medium speed, roughly €2-5/month of electricity in continuous use. The efficient routine: maximum speed for 30 minutes when entering a room or after cooking, then automatic/quiet mode to maintain. Models with a PM2.5 sensor do exactly this on their own.