A portable air purifier is a filter with a fan. Matching its airflow to your room, avoiding ozone and knowing what filters cannot do matter far more than the extra features.
Turn an air purifier’s box around and the figures worth finding are small and unglamorous: three CADR numbers, one each for tobacco smoke, dust and pollen, printed on an independent certification label. Filter-stage counts, app dashboards and “air changes per hour” claims are easier to market than to compare. This guide works through the decisions in the order that affects results most.
CADR, the clean air delivery rate, describes how much particle-free air a unit delivers; a higher figure means more particles removed and a larger area served. It is a particle rating only, and it is usually measured at the highest fan speed. Health Canada’s guidance points buyers to units certified by the Association of Home Appliance Manufacturers (AHAM), whose label lists separate CADR values for tobacco smoke, dust and pollen because each uses a different particle size.
For fine particles, including wildfire smoke, Health Canada says to look at the tobacco smoke figure. Its rule of thumb is that the smoke CADR should be at least two-thirds of the room’s area in square feet. A 20 m² living room is roughly 215 sq ft, which points to a smoke CADR of about 145 or more. The US EPA gives a similar estimate of roughly 65 CADR per 100 sq ft, assuming ceilings of about 2.4 m (8 ft).
One caveat for readers outside North America: the AHAM label is the scheme cited by Canadian and US agencies. We did not verify an equivalent label in the UK or Australia for this article, so where it is missing, look for a manufacturer’s stated airflow for particles and the test method behind it, and treat a bare “covers 60 m²” claim with caution.
| Technology | What it targets | Main caveat |
|---|---|---|
| HEPA filter | Fine particles such as smoke, dust and pollen | Most units with one do not remove gases; filters need replacing |
| Activated carbon (or similar absorbent) | Some gases, including volatile organic compounds (VOCs) | No widely used performance rating; thicker carbon beds work better, per the EPA |
| Electrostatic precipitator or ioniser | Particles | Can produce ozone; look for ozone certification |
| UV, photocatalytic or plasma units | Often marketed for gases and germs | The EPA says these have not been shown to remove gases effectively in residential units |
| Ozone generator | Sold as a freshener or sanitiser | Deliberately produces ozone, a lung irritant; avoid in occupied homes |
Health Canada notes that HEPA filters are commonly used to reach a high CADR, and that both airflow and filter efficiency determine performance. A purifier with a good filter and a weak fan will clean a room slowly; a strong fan behind a poor filter will not capture much. This is why a single CADR figure is more informative than a list of filter layers.
The harder cases are ionisers and electrostatic precipitators, which are sold as ordinary air cleaners but can emit ozone as a by-product. Health Canada recommends models certified by the California Air Resources Board (CARB) or meeting the CSA 22.2 187-15 ozone standard. CARB’s limit for electronic air cleaners is 0.050 ppm, and certified products carry the wording “Meets California ozone emissions limit: CARB certified” and appear on its public list. Be wary of terms such as “activated oxygen” or “super-oxygenated air”, which CARB flags as warning signs.
Health Canada and the EPA agree on the main limit: removing the source and ventilating with clean outdoor air are the most effective measures, and filtration supplements them. Cooking, tobacco smoke, candles and incense, dry dusting and sweeping, and vacuuming with a non-HEPA machine are all listed by Health Canada as sources of indoor fine particles. Cooking with the range hood on, snuffing candles rather than blowing them out, and damp-mopping cost nothing. A good vacuum with proper filtration belongs in the same plan.
Purifiers also do not fix damp. The EPA states that air cleaners cannot solve mould problems, which need the moisture source fixed; Health Canada suggests keeping indoor relative humidity between 30% and 50%. And before opening windows for ventilation, check the local air quality forecast, because on smoky or smoggy days outdoor air can be worse than indoor air.
Particles from cooking are within a HEPA filter’s reach, but smells are largely gases. Health Canada says most air purifiers do not remove gases, and carbon filters have no widely used performance rating, so expect partial help at best. Using the range hood and ventilating are more reliable.
Health Canada suggests choosing the highest smoke CADR your budget allows for fine particles, but the unit also has to fit your room and tolerance for noise. A very high-capacity unit in a small bedroom may be pointless if you cannot stand it on high.
Health Canada advises using the tobacco smoke CADR when choosing a unit for wildfire smoke, because the smoke contains fine particles (PM2.5). Keep windows and doors closed while it runs.
Yes. Health Canada says filters do not replace ventilation, and that opening windows when outdoor air is clean is one of the most effective measures.
Not necessarily. The EPA notes that such systems typically run less than 25% of the time during heating and cooling seasons, so filtration is limited unless they run longer. If your system can accommodate a higher-rated filter, the EPA suggests MERV 13 or above, after checking with an HVAC technician.
If you are weighing other small upgrades, the Home Gadgets section has more, and smart plugs are one way to put a unit on a timer. Check the plug’s load rating against the purifier’s first.
How we research. Based on manufacturer documentation and the sources listed below. Know Your Gadget did not test products for this article. See our editorial policy.
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