1. Published documents, not a test unit
We do not own test units and we do not run a lab, so nothing here is presented as our own measurement. Every model is worked out from material anyone can open: the manufacturer's published specification sheet and manual, the AHAM Verifide registry entry, the CARB certified device list, and the maker's own filter prices and replacement intervals. Where a number is the maker's own claim and no registry confirms it, the page says so.
This site previously described its method as reading aggregated Amazon reviews and reported what "owners report". That was removed in September 2026: the review data was not ours to republish, the sample was not something a reader could check, and the pages now stand on documents instead.
2. CADR math: the 2/3 rule - and checking the number itself
Manufacturers publish a CADR (Clean Air Delivery Rate) number in CFM, and a "recommended room size." Those recommended sizes are frequently optimistic. The rule of thumb we use instead: for continuous, meaningful air changes, the unit's CADR (in CFM) should be at least two-thirds of your room's area in square feet. A purifier rated for a 300 sq ft room under that math should comfortably handle a 200 sq ft room at a more aggressive filtration rate - which matters a lot more when there's a litter box or a bird cage in it.
We don't stop at the manufacturer's own CADR figure, either. Every model is checked against AHAM Verifide, the independent third-party registry that actually tests CADR, and separately against CARB's certified device list for ozone safety - a different registry testing a different thing. Full results for all 9 models are on our registry check page, and the CARB classification gets its own dedicated breakdown of what it does and doesn't mean.
3. Real cost of ownership, not just the price tag
A cheaper purifier with an expensive, frequently-replaced filter can cost more over three years than a pricier unit with a cheap annual filter. Every review on this site includes a filter-cost-per-year calculation: published filter price × the replacement interval the manufacturer states. We don't publish device prices - those change constantly and Amazon's own listing is the accurate source - but filter economics are a genuinely useful, durable number, checked directly against each manufacturer's own support pages rather than assumed from the box. See our true filter costpage for the full check across all 9 models - 8 of 9 needed a correction.
4. Noise: the manufacturer's own decibel range
We report the manufacturer's decibel range across fan speeds, and the speed that range is measured at, because the quoted "as low as 24 dB" figure is nearly always the lowest speed, not the one a litter box room needs.
5. What we do not do
We do not quote or summarise customer reviews, we do not publish star ratings or review counts, and we do not describe a unit as tested when nobody here has tested it. If a claim on this site cannot be traced to a manufacturer document or a registry entry, it should not be on the page - tell us and we will remove it.
6. No sponsored placements
We don't accept payment from manufacturers to influence rankings. Rankings are based on data, not deals. Where we earn money is through the Amazon Associates program when you buy through a link on this site - see our Affiliate Disclosure for the details.