How to choose an air purifier

Q: What is CADR?

Clean-air delivery rate (m³/h): how much filtered air the unit delivers per hour. The most useful number for comparing and for sizing to your room.

Ignore the big marketing claims. To choose well, look at five things: CADR, filtration, noise, running cost and room size.

1. CADR — airflow is everything

CADR (clean-air delivery rate) is the most useful number: how much filtered air per hour. Match CADR to your room to change the air ~4–5 times an hour.

2. HEPA vs MERV-13

Both capture the PM2.5 that matters. HEPA grabs a little more of the very finest particles but chokes airflow and often needs pricey cartridges. MERV-13 captures ~93% while moving far more air — often more clean air per euro at home.

3. Noise and 4. cost

Under 35 dB you can run it overnight. At ~15 W it costs about €15 a year; a 100 W tower is closer to €60.

5. Room size

Room	Floor area	CADR to aim for
Bedroom / office	up to 15 m²	150+ m³/h
Double bedroom / living room	15–25 m²	250–350 m³/h
Large living room	25–40 m²	400–550 m³/h
Open plan	40–60 m²	550–700 m³/h