The short answer
- Yes for particles: smoke, dust, pollen, pet dander and mould spores.
- Partly for smells, and only with a decent carbon filter.
- No for carbon dioxide, humidity, or gases such as nitrogen dioxide from gas cooking.
What the research says
In a Canadian study of homes affected by forest-fire and wood smoke, portable HEPA purifiers cut indoor fine particles by 55% in winter and 65% in summer, on average.
A 2016 review went further, arguing portable purifiers should be a front-line public health tool for landscape fire smoke. The US EPA agrees they work, but as a supplement to cutting pollution at the source and ventilating, not a replacement.
When they don't work
- Too small. Box coverage assumes one air change an hour. You want four or five.
- Doors and windows open. It can't keep up with the outside.
- Evaporative cooler on during smoke. It pulls smoke in faster than any purifier removes it.
- Clogged filter. Airflow drops as it loads up.
- Switched on too late. Leave it on auto rather than reacting to smoke.
How to make one work
- Size it properly with the room calculator.
- Close the door. Clean one room well rather than the whole house badly.
- Run it all the time on auto, and on high during smoke.
- Change filters on time and vacuum the pre-filter.
What's a waste of money
- Ozone generators and heavy ionisers. Ozone irritates the lungs. The US EPA advises against ozone generators indoors.
- Tiny desktop units. Too little clean air for a real room.
- Paying for design. The Dyson vs Levoit comparison shows how much.
See the best purifiers in Australia
Sources
- Barn P. et al. (2008). Infiltration of forest fire and residential wood smoke: an evaluation of air cleaner effectiveness. Journal of Exposure Science and Environmental Epidemiology.
- Barn P. et al. (2016). Portable air cleaners and the public health response to landscape fire smoke. Environmental Health.
- US EPA: Guide to air cleaners in the home and strategies to reduce smoke exposure indoors.