CADR, Filters and What It Costs to Run

This is the section the rest of the site is built on. If you read one page here, make it the CADR explainer — everything else on Dander Down is an application of it.

What CADR is. Clean Air Delivery Rate is the volume of genuinely clean air a machine delivers per minute, in cubic feet, measured under ANSI/AHAM Standard AC-1. It is reported as three numbers, because the test uses three pollutants of different particle sizes: tobacco smoke (the smallest, and the number room sizing is built on), dust, and pollen (the largest). A unit rated 265 smoke / 259 dust / 244 pollen moves 265 cubic feet of smoke-free air per minute.

The single most useful property of CADR is that it is a combined figure. It captures filter efficiency and airflow together, which means a machine cannot game it by fitting a superb filter to a weak fan, or a strong fan to a mediocre filter. That is precisely why marketing prefers to talk about filter grade in isolation.

Certified is not the same as claimed, and this is the site's organizing principle. Anyone can print a CADR figure. Two public registers contain independently verified ones:

AHAM's VERIFIDE program maintains a directory of certified room air cleaners; AHAM retains an outside laboratory to test sample units and verify the manufacturer's claimed ratings. EPA's ENERGY STAR program maintains a database of certified room air cleaners, where certification requires testing to the same AC-1 standard through an EPA-recognized certification body, and which additionally publishes each unit's measured ozone emissions and certified annual energy use.

A model listed in either has a number somebody other than the seller stands behind. A model in neither has a number the seller stands behind alone. That is not an accusation — manufacturer figures are often perfectly accurate — but it is a real difference in evidence, it is checkable in about a minute, and as far as we can find, no competitor in this category makes it their organizing principle. Some popular and well-regarded machines are in neither register. We say which, on every card, every time.

What the certification does not tell you. Being straight about this costs nothing and is the strongest thing on the page. CADR is measured against smoke, dust and pollen under a specific laboratory protocol. It is not a pet-dander test — no such certification exists. It is measured on a new filter in a sealed chamber, not a six-month-old filter in a room with a door that opens. It says nothing about build quality, failure rates, or whether the machine will still be running in five years, and we cannot assess any of those without owning units, which we do not. CADR is the best comparable number available in this category. It is not a complete description of a machine, and anyone who tells you it is has something to sell.

Cost is the half of the decision nobody publishes. Two machines with almost identical certified output can differ threefold in what they cost to run. Among the units on this site, annual certified energy use runs from 95 kWh to 657 kWh. At the current U.S. average residential electricity price that is roughly $17 a year against $121 a year — for machines whose purchase prices are not three times apart. Over a five-year life the running cost can exceed the purchase price and reverse which unit was actually cheaper.

Filters are the other half, and they are where the arithmetic gets genuinely unpredictable: a filter interval published for general use is optimistic in a house with a shedding dog, because hair loads a filter faster than laboratory dust does. We show the arithmetic on both, with the assumptions stated — electricity rate, hours, filter interval and where each figure came from — so you can substitute your own rate and rerun it. That is the point of showing the working rather than just the answer.