Marketing promises "hospital-grade air" in a bedroom. Do air purifiers work? For fine particles — yes, if the unit is true HEPA (or equivalent), sized for the room, and maintained. They do not remove ozone or CO and they cannot fix a home that imports smoke through leaky windows all day.
What HEPA filters actually capture
True HEPA filters trap most PM2.5, dust, pollen, and smoke particles that pass through the fan. CADR (clean air delivery rate) and room volume matter: an undersized unit on high in a large open-plan living area will struggle. Run on auto if available; replace filters on schedule — a clogged HEPA moves air without cleaning it.
Purifier vs open window
When outdoor AQI is green, ventilation often wins — fresh air dilutes indoor cooking and CO₂ buildup. When outdoor is orange or smoke-filled, seal up and let the purifier work. The mistake is purifying while windows wide open to traffic fumes.
- Smoke week: purifier on, windows closed, check filter life after.
- Good outdoor air: ventilate first; purify for dust and pets indoors.
- Avoid ionisers that produce ozone as a "fresh" smell.
- One purifier per closed room beats one weak unit for the whole flat.
Pair with data
A cheap indoor PM monitor or checking outdoor AQI before you ventilate closes the loop. Purifiers are a tool for bad-air days and strong indoor sources — not a reason to ignore what is happening outside.
Check outdoor AQI on Aether first — then decide whether today is a ventilate day or a purifier day.
Check live air quality on Aether