What CADR actually means

This is the page the rest of this site is built on. Everything else here is an application of what follows.

CADR is reported as three numbers because the test uses three pollutants of different particle sizes: tobacco smoke (the smallest, and the figure room sizing is built on), dust, and pollen (the largest). A unit rated 265 smoke / 259 dust / 244 pollen delivers 265 cubic feet of smoke-free air per minute.

The single most useful property of the measure is that it is a combined figure. Filter efficiency alone tells you nothing — a superb filter with a feeble fan cleans very little air. Airflow alone tells you nothing either — a powerful fan pushing air through poor media just moves dirty air around. CADR multiplies the two, which means it cannot be gamed from either direction.

That is precisely why marketing prefers to talk about filter grade in isolation. “True HEPA” is a claim about one half of an equation.

Anyone can print a CADR figure on a box. Two public registers contain independently verified ones.

AHAM VERIFIDE

AHAM operates a certification program for room air cleaners and retains an outside laboratory to test sample units and verify manufacturers’ claimed ratings. Certified models appear in a public directory you can search by brand.

ENERGY STAR

EPA’s certified room air cleaner database requires testing to the same ANSI/AHAM AC-1 standard through an EPA-recognized certification body. It additionally publishes each unit’s measured ozone emissions and certified annual energy use, neither of which AHAM’s directory carries in the same form.

AHAM publishes the rule in one sentence: the CADR of your air cleaner should be equal to at least two-thirds of the room’s area. Its directory runs the same relationship backward to produce the suggested room size on the certification seal — room square feet = smoke CADR × 1.55 — and states that this is based on the cleaner’s ability to clean and circulate the room’s air 4.8 times per hour, at an assumed 8-foot ceiling.

That assumed ceiling is the part that gets dropped. AHAM says directly that if your ceilings are higher than 8 feet, an air cleaner rated for a larger room will be necessary. The calculator applies both, with the arithmetic shown.

Manufacturers commonly advertise coverage at one air change per hour rather than AHAM’s 4.8. Both figures come from the same test data and both are technically accurate. Only one describes a machine keeping up with a room that keeps getting dirty.

Saying this plainly costs us nothing and is the strongest paragraph on the page, because it is the thing no competitor making a testing claim can afford to write.

• It is not a pet-dander test. The standard uses smoke, dust and pollen because they are reproducible in a laboratory. No certification for pet allergen exists.
• It is measured on a new filter in a sealed chamber. Your filter will be six months old and your door will open.
• It is the maximum-setting figure. Run the machine on low — which in a bedroom you will — and the effective rate is a fraction of it. Nobody publishes per-speed CADR.
• It says nothing about build quality or reliability. We cannot assess those without owning units over years, and we do not.

CADR is the best comparable number available in this category. It is not a complete description of a machine, and anyone telling you it is has something to sell. Our full method, including where it runs out.