What does CADR mean?
CADR stands for Clean Air Delivery Rate and states how much cleaned air an appliance delivers per hour, measured in m³/h. A CADR of 240 m³/h means the appliance delivers 240 cubic metres of filtered air per hour. The higher the value, the faster the room air is circulated.
The key points in brief
- Which CADR value for which room size? Calculate: floor area × room height × desired air changes.
- Is the “suitable up to X m²” figure on the packaging correct? Often not for allergy sufferers: manufacturers frequently calculate with only one to two air changes per hour.
- Which filter matters in an air purifier? A HEPA filter (H13) for particles such as pollen and fine dust, plus activated carbon against odours and gases.
Details and reasoning in the article, FAQ at the end
CADR is the only reliable performance figure. The manufacturer's “suitable up to X m²” figure is derived from it, but often with very optimistic assumptions (see below).
The formula: air changes per hour
What matters is how often the whole room's air passes through the filter per hour: the air change (Air Changes per Hour, ACH). The rules of thumb:
- Normal use: 2 to 3 air changes per hour are enough for generally better air.
- Allergy sufferers, pets, pollen, smoke: 4 to 5 air changes per hour, so the air is completely cleaned once every 12 to 15 minutes.
The calculation: required CADR = floor area × room height × desired air changes. With a standard ceiling height of 2.5 m:
- 15 m² bedroom, allergy sufferers (5×): 15 × 2.5 × 5 = ≈ 190 m³/h CADR
- 20 m² room, allergy sufferers (5×): 20 × 2.5 × 5 = ≈ 250 m³/h CADR
- 30 m² living room, normal (3×): 30 × 2.5 × 3 = ≈ 225 m³/h CADR
- 40 m² living-dining area, normal (2.5×): 40 × 2.5 × 2.5 = ≈ 250 m³/h CADR
Rule of thumb to remember: an appliance with around 240 to 250 m³/h CADR cleans a 20 m² room to allergy-friendly standard (5×) or a 30 to 40 m² room for normal needs.
Why “up to 50 m²” on the pack is often misleading
Many manufacturers calculate the maximum room size with only one to two air changes per hour. For allergy sufferers that is too little, as the air is then circulated only every 30 to 60 minutes. So the rule is: for allergy sufferers, halve the stated room size. An appliance “for 50 m²” is realistically more of a 25 m² appliance for allergy sufferers.
Better than looking at the m² figure: calculate with the CADR and your desired air change, and then you won't go wrong.
What matters besides CADR
- HEPA filter (H13): retains 99.95 % of particles from 0.3 µm, such as pollen, fine dust and pet hair. A must for allergy sufferers.
- Activated carbon: binds odours and gases (kitchen, smoke, fumes). A pure HEPA filter cannot do that.
- Washable pre-filter: catches coarse dust and extends the life of the expensive HEPA filter, saving running costs. Models such as the Levoit Vital 100S include one.
- Noise in night mode: for the bedroom the lowest setting should be under 25 dB. The Philips AC0650 comes in at 19 dB, the Levoit Core 300S at 22 dB.
The direct comparison of “more power against cheaper & quieter” is shown in the head-to-head Levoit Core 300S vs Philips AC0650. For large rooms with a washable pre-filter against compact with automatic sensor control, the head-to-head Levoit Vital 100S vs Xiaomi Air 4 Compact helps.
Bedroom vs. living room: the right choice
Bedroom (10 to 16 m²): noise matters most here. An appliance with 180 to 240 m³/h CADR and a genuine whisper/night mode under 25 dB is enough; better a somewhat stronger appliance running on a low, quiet setting than a small one at full stretch.
Living room (20 to 40 m²): more CADR is welcome here (240 m³/h upwards), and noise is less critical in the daytime. Activated carbon is worthwhile against cooking and living odours.
Which models do this in which price range is in the air purifier comparison for the bedroom.
Verdict
Ignore the optimistic “up to X m²” figure and calculate via CADR: area × height × air changes gives the required value, 5× for allergy sufferers, 2 to 3× for normal needs. Around 240 m³/h CADR covers a 20 m² room to allergy-friendly standard. Also look for HEPA H13, activated carbon, a washable pre-filter and, for the bedroom, a quiet night mode. Suitable appliances are in the air purifier comparison.
Frequently asked questions
Which CADR value for which room size?
Calculate: floor area × room height × desired air changes. For allergy sufferers 5 air changes per hour apply, normally 2 to 3. A 20 m² room therefore needs around 250 m³/h CADR for allergy sufferers, and appliances with about 240 m³/h cover that.
Is the “suitable up to X m²” figure on the packaging correct?
Often not for allergy sufferers: manufacturers frequently calculate with only one to two air changes per hour. For allergy-friendly cleaning, you should roughly halve the stated room size.
Which filter matters in an air purifier?
A HEPA filter (H13) for particles such as pollen and fine dust, plus activated carbon against odours and gases. A washable pre-filter extends the life of the HEPA filter and lowers running costs.