Air purifier room size and CADR
CADR, the clean air delivery rate, tells you how much filtered air a purifier delivers per hour. Matching it to your room volume is more reliable than a "suitable for X m²" claim.
The calculation
Required CADR (m³/h) = room volume (m³) × air changes per hour.
Room volume is floor area × ceiling height. A 20 m² room with 2.4 m ceilings is 48 m³. At 3 air changes an hour you'd want about 144 m³/h.
- General use: 3 ACH
- Allergies, pets or smoke: 5 ACH
- Quiet bedroom: 2 ACH (lets you use a lower, quieter setting)
Why maker room-size claims differ
AHAM's room-size rating assumes about 4.8 air changes an hour. Many brand claims use fewer, which makes a purifier look suitable for a larger room. We show the claim and the air changes behind it where a source gives them.
Reading CADR figures
Check which pollutant and standard the figure is for. Where a listing gives a single headline number without saying, we mark it as not stated.
HEPA labels
- H13 or H14 means the filter is graded under the European standard. We only show these when a source confirms them.
- "HEPA-type" or "99% HEPA" is not the same thing and we label it "not confirmed".
Health
Evidence that a purifier on its own improves asthma is limited. We don't make health claims, and if you have a medical condition you should ask your doctor.