Editorial policy
Quick answer
Nothing on this site was tested in person, no price or product identifier here was invented, and where a question has no honest answer the page says so instead of guessing.
No fabricated testing
We have not run an air purifier in a test chamber, and no page here claims otherwise. The research comes from published manufacturer specifications, the published test standards those specifications are measured under, and owner reports. Where a page says a machine does something, it is because the listing or the manufacturer says so.
No invented numbers
Every product on this site comes from a real listing with a real identifier, a real image and a real price. A listing that does not return all three is left out rather than patched with an estimate. Where a machine publishes no usable airflow figure, the page says that too, and does not derive one from a coverage claim with no air change rate behind it.
Standards, conventions and guidance are labelled
AHAM AC-1 and ASHRAE 52.2 are standards: published test methods with defined conditions. The two thirds rule is a convention, a shopper's rule of thumb. The four to five air changes an hour figure for allergy households is guidance. These are three different kinds of claim and this site names which is which rather than blending them into one confident sentence.
The tools are allowed to refuse
If no single machine can deliver the air change rate a room needs, the calculator says so and suggests two units or a smaller space. If a humidity target would condense on the windows at the outdoor temperature entered, it refuses that too. An answer that cannot be achieved is not an answer, and selling the nearest machine that falls short would be the easy thing to do here.
Health claims
Filtration reduces the airborne concentration of particles, at a rate that can be calculated. That is what this site claims and it is the limit of what it claims. No page here says a machine treats, prevents or relieves any condition, and none will.