If you’re buying an air purifier to deal with pollen, dust-mite debris, pet dander, or mold spores, almost every number on the box is designed to sell you the wrong thing. Here’s what actually predicts whether a purifier will clear the air in the room you put it in — and where to find the figures that matter.
CADR is the number that matters
Clean Air Delivery Rate (CADR) is the volume of filtered air a purifier actually delivers, in cubic feet per minute. It’s the one spec that’s independently tested to a common standard: the AHAM Verifide program puts units through a sealed-chamber test and publishes a CADR for dust, pollen, and smoke. Because the three are measured against progressively finer particles, smoke CADR is the most demanding of the three — and the best single proxy for how a purifier handles the fine allergen particles that stay suspended in the air you breathe.
A purifier with an AHAM-verified smoke CADR of 240 CFM will out-clean one rated 130, full stop. Everything else — app, sensor, styling — is a tiebreaker. We collected the AHAM CADR (and, where a model isn’t AHAM-listed, the independently lab-measured PM1 CADR) for every unit we looked at in the Air Purifier CADR data table, which you can sort by any column.
Ignore the “up to X sq ft” claim
The coverage number on the box is almost always calculated at one air change per hour — enough to notice a difference, nowhere near enough for allergies. For allergy and asthma relief you want roughly five air changes per hour, which means the honest coverage figure is about a third of the advertised one. Blueair’s “3,235 sq ft,” for instance, is a 1-ACH figure; the realistic allergy coverage of that unit is closer to 635 sq ft. Every coverage figure in our data table is the CADR-derived 5-ACH number, not the marketing claim.
True HEPA vs. “HEPA-type” vs. HEPASilent
For allergens you want media rated to capture 99.97% of particles at 0.3 micron — the standard “true HEPA” threshold, which covers pollen, dander, dust-mite waste, and mold spores. Watch for two wrinkles:
- “HEPA-type” / “99% at 2 micron” filters are a real step down — avoid them for allergies.
- Blueair’s HEPASilent and similar electrostatic-assisted systems post strong CADR at very low noise, but they aren’t classic mechanical true-HEPA. They perform well in testing; purists and some asthma sufferers still prefer straight mechanical HEPA (or H13 medical-grade media).
One more caution: some ionizing purifiers (Winix’s PlasmaWave, for example) produce trace ozone, which is an irritant for asthma. It’s usually a switch you can turn off — but know it’s there.
Filter cost is part of the price
Recurring filter cost varies more than five-fold across comparable units — from about $30/year for a small Levoit to $200+/year for a multi-stage IQAir. Over three years that gap can exceed the price of the machine, so we treat it as a first-class factor rather than a footnote. It’s a sortable column in the data table.
Where the on-site data comes from
The figures we rank on are transcribed from AHAM’s Verifide directory and independent lab testing (notably HouseFresh’s 130+ real-world PM1 measurements and RTINGS’ lab data), with maker claims flagged as such. Our opinionated shortlist — Top 10 Air Purifiers for Allergies — is built directly on that table: same numbers, plus a pick for each use case (best overall, best large room, best budget, best for pets, best for asthma).