Find the purifier that fits your room.

It depends on whether you have a particle problem you cannot remove at the source, and that is worth being honest about. A purifier moves airborne particles through a filter; it does nothing about the source itself. If the smell is damp, the answer is humidity, not filtration. If it is a gas cooker, extraction and an open window do more than any unit on this site. Where a purifier does earn its place is with particles that keep arriving and cannot be stopped — pollen through open windows in spring, wildfire smoke, dust from a nearby road, cat or dog dander in a flat. Start with the source; a purifier is what you add when the source is outside your control.

CADR is Clean Air Delivery Rate: how much particle-free air a unit delivers per minute, measured separately for smoke, dust and pollen. It is the only figure that lets you compare two purifiers directly, because it combines how well the filter captures with how much air the fan actually moves. A superb filter behind a weak fan gives a poor CADR. The number matters most when an independent body measured it: AHAM Verifide means a laboratory did. A CADR with no AHAM entry is the brand’s own figure, and nobody outside the company has checked it.

Because a coverage figure is meaningless without the air-change rate behind it, and manufacturers pick different ones. The same machine can be sold as "1,051 sq ft" at one air change per hour or "219 sq ft" at 4.8 — both true, same unit, numbers that differ by a factor of five. AHAM’s convention is 4.8 air changes an hour. On every review here we print the basis next to the number, and where the manufacturer does not publish one we say so instead of quietly assuming.

No, and the label is weaker than it looks. There is no public certification a manufacturer can obtain for a consumer air purifier: every HEPA claim on a box is the maker’s own. AHAM’s directory lets brands declare their own filter class, and the same directory carries entries reading "HEPA-Type" next to others reading "True HEPA" or "H13". That is why every HEPA mention on this site is attributed to whoever said it, rather than stated in our own voice.

It is the legal minimum, not a feature. Since 2010 California has required portable indoor air cleaners sold or shipped into the state to be certified, which caps ozone emission. Almost every unit worth buying has it, so its presence tells you little. What is worth knowing is its ABSENCE, or a mismatch between the model on the listing and the model on the certified list — which is a real thing that happens, and something we check for each review.

That is the running cost, and it is the part of the price that is not on the price tag. Manufacturers state intervals between roughly 6 and 12 months, but the interval always rests on a usage assumption — hours per day, at what speed — and that assumption is the part most listings leave out. Our filter guides print the interval together with the assumption behind it, and say which stages are washable and which are not, because a washable pre-filter is one fewer thing you have to keep buying.