How this site is researched

The arithmetic

Required clean air delivery rate equals floor area times ceiling height times air changes per hour, divided by sixty. That is the spine of the site. It is unit conversion rather than a rule of thumb, and every sizing page shows the working.

The familiar two thirds rule is the same calculation with an eight foot ceiling and five air changes an hour already chosen, since eight times five divided by sixty is 0.667. Saying so is more useful than repeating the rule, because it shows exactly where the rule stops applying.

The products

The catalog is built from real listings. A listing that does not return an identifier, an image and a price is rejected rather than filled in. Prices, images and product names on this site were never estimated, rounded or written from memory.

Figures read from a listing are marked as claims, because that is what they are. A coverage area in square feet is a marketing figure unless the listing also states the air change rate behind it, and where it does not, this site refuses to convert it into an airflow.

What we do not do

We do not test machines. Nothing here was measured in a chamber by us, and no page claims it was. We also do not recommend ozone generators at any price, and we do not describe any product as treating a medical condition.

When we cannot answer

The calculators return a refusal rather than a number when the question has no good answer: a room too large for any single machine at the rate asked for, a humidity target that would condense on the windows, a space with standing water in it. Each refusal comes with what to do instead.

Corrections

If a figure here is wrong, we want to know. The contact page reaches us directly, and the editorial policy sets out the rules we hold ourselves to.