Air purifier CADR: compare clean-air delivery with the actual room

By the Breezewold team

An air purifier's room-size claim needs a little context. Find its clean air delivery rate, the units used and the fan setting associated with that figure before comparing it with another machine.

Start with the pollutant and the number

The US EPA: Guide to Air Cleaners in the Home explains that CADR concerns particle removal. It is not a general rating for gas removal. EPA also notes that airflow depends on fan speed and that its room-sizing chart assumes a particular ceiling height. This is technical US guidance, not a UK product approval or a health promise.

That distinction gives you three useful questions: what is being filtered, at what delivery rate, and under which conditions? A HEPA label alone does not answer all three.

Put the room into cubic metres

Measure length, width and ceiling height in metres. For an invented rectangular room measuring 4m × 3m × 2.5m, volume is 30m³.

Suppose a hypothetical purifier has a verified particle CADR of 150m³/h at the setting you intend to use. Dividing 150 by 30 gives 5 room volumes per hour as an equivalent clean-air delivery calculation.

This is a way of reading the units, not a recommendation that five is the correct target for your home. It does not mean every corner receives identical filtration or that the whole room is perfectly cleaned every twelve minutes. Do not substitute the fan's raw airflow figure for CADR.

Make a fair shortlist

Record the following for each exact model:

Item	What to write down
CADR	Value, units and stated test basis
Usable setting	Evidence for the speed you expect to run
Room	Measured volume and whether doors stay open
Ownership	Replacement-filter identity, availability and instructions
Placement	Required clearance from the manual

If a product quotes only a maximum room area, ask what ceiling height and air-delivery assumption produced it. Keep an unanswered question visible instead of treating unlike claims as equivalent.

Check the arrangement before spending more

Use the manufacturer's placement instructions and keep the airflow path clear. Decide whether the machine will be used in one closed room or moved between spaces; those are different arrangements to discuss with the supplier.

Keep particle filtration separate from ventilation, moisture and CO2 questions. Use the related monitoring guide for CO2 readings. A single purifier specification cannot establish that every indoor-air concern has been addressed.

FAQs

Start with these quick answers, then use the full guide for the checklist and source details.

Is fan airflow the same thing as CADR?

No. For a comparison, request the particle clean-air delivery figure and its units; do not silently substitute the fan airflow specification. US EPA: Guide to Air Cleaners in the Home explains what CADR measures.

Why does ceiling height matter when comparing room claims?

A floor area does not describe the full room volume. EPA identifies a ceiling-height assumption in its sizing chart. Measure your own room and ask how the advertised area was calculated. US EPA: Guide to Air Cleaners in the Home

Does particle CADR rate gas removal too?

No. EPA treats particle CADR separately from gas filtration. Check the relevant filter and evidence for the substance of concern rather than applying a particle number to everything. US EPA: Guide to Air Cleaners in the Home