How to read an air purifier spec sheet
In this guide
CADR — and why the number is cherry-picked
CADR (Clean Air Delivery Rate) is measured in cubic metres per hour. It is the volume of clean air the unit produces, and it is the only figure that tells you how fast the machine actually cleans.
The problem: CADR is measured at maximum fan speed, which is the loudest setting. Manufacturers are not required to publish CADR at quieter speeds, and many do not.
Filter claims that mean nothing
| Claim on the box | What it actually means |
|---|---|
| "HEPA" | Nothing on its own — HEPA is a family, not a grade. Ask which class. |
| "HEPA-type" / "HEPA-like" | Not HEPA. Usually H10–H11 or an electrostatic media. |
| "True HEPA" | Better, but still no grade stated. Push for H13. |
| "HEPA H13" | 99.95% at 0.3 µm. This is the one worth paying for. |
| "99.9% filtration" | At what particle size? Almost always a flattering size. |
| "Washable HEPA" | Washing damages the fibre structure. Efficiency drops with every wash. |
"Covers 60 m²" — what that actually says
Coverage claims are marketing, not engineering. They assume a specific ceiling height and a specific air-change rate, and the manufacturer chooses both.
Convert it yourself instead: take the claimed CADR, divide by 3, and that is the realistic room volume in cubic metres at a reasonable air-change rate. Then divide by your ceiling height to get square metres.
Example: CADR 300 m³/h ÷ 3 = 100 m³. At a 2.5 m ceiling, that is 40 m² — not the 60 m² on the box.
Noise figures
Look for decibels at each fan speed, not one number. A "24 dB" claim usually refers to the lowest speed with airflow you cannot feel.
- Under 30 dB — usable overnight in a bedroom
- 30–45 dB — noticeable but tolerable in a living room
- 45 dB+ — you will not leave it running while you are in the room
Power and running cost
Power draw is listed in watts, and it varies enormously between fan speeds. A unit rated 60 W may draw only 8 W on low.
To estimate yearly electricity: watts ÷ 1000 × hours per day × 365 × your rate per kWh. Our filter cost calculator does this alongside the filter cost, which is usually the bigger number.
Red flags on a spec sheet
- No CADR at all — only "covers X m²". They are hiding the number.
- No filter class stated — "HEPA" with no H-number is unverifiable.
- No replacement filter listed — check availability before buying, not after.
- Noise in "dB(A)" without a speed reference — meaningless.
- Ioniser or UV as the headline feature — these do not replace mechanical filtration, and some ionisers produce ozone.