Air purifiers vs houseplants vs ventilation: an honest comparison

Every pollution season brings the same three suggestions: buy a purifier, fill the house with plants, or just open the windows. They solve different problems, and mixing them up leads to wasted money or worse air.

What each one is good at

• HEPA purifier: strong on fine particles, weak on gases unless it has a large carbon filter, no effect on stuffiness
• Houseplants: negligible effect on particles, gases or stuffiness at normal numbers
• Ventilation: strong on gases, odours and stuffiness; helps or hurts on particles depending on the air outside

Air purifiers

A purifier with a genuine HEPA filter physically traps particles. In a closed room of the right size it can bring PM2.5 down substantially within an hour. That makes it the only one of the three that reliably helps on a smoggy day.

What to check before buying:

• CADR suited to the room; aim for a unit rated for a larger room than yours
• Real HEPA, not 'HEPA-type' or 'HEPA-like'
• Filter replacement cost per year, which can exceed the purchase price over time
• No ioniser or ozone function, or one you can switch off

Running costs are usually modest. Many units draw roughly as much power as a ceiling fan on a medium setting.

Houseplants

The idea that plants clean indoor air comes from a well-known 1989 NASA experiment that used small sealed chambers. Later reviews found that in a real home, with normal air exchange, you would need an enormous number of plants to match even basic ventilation. Plants are good for mood, humidity and the look of a room. They are not an air-cleaning device.

Ventilation

Opening windows is the best way to remove carbon dioxide, cooking smells and gases from paints and cleaners. The catch is obvious in smog season: you also let in outdoor particles. The answer is timing. Air rooms briefly when outdoor AQI is lower, often in the afternoon, and close up during the night and early morning peaks.

Kitchen and bathroom exhaust fans are targeted ventilation and should run whenever you cook or shower.

The combination that works

Use ventilation to keep air fresh, a purifier to remove particles when the outdoor air is poor, and plants because you like them. Spend money in that order. A modest purifier in the bedroom, used correctly, will do more for your lungs this winter than a living room full of snake plants.