Beyond CADR: Rethinking How We Measure Air Purifier Performance

For decades, there has been one number to rule them all in the world of air purifiers: the Clean Air Delivery Rate, or CADR. Stamped on the box of nearly every major air purifier, this metric has served as the primary benchmark for consumers, a seemingly straightforward way to compare how quickly a device can clean a room.

Developed by the Association of Home Appliance Manufacturers (AHAM), the CADR rating measures how many cubic feet of clean air a purifier delivers per minute for three specific particle types: smoke, dust, and pollen. A higher number means a faster clean. It’s simple, standardized, and has driven product design for years. But as air purification technology evolves, a critical question is emerging: Is this 20th-century metric adequate for 21st-century threats? The rise of technologies like PECO, which operate on principles entirely alien to CADR’s design, suggests we may need to look beyond this single number.

The CADR Formula: Speed Equals Power

At its heart, the CADR test is a race against time. A purifier is placed in a sealed 1,008-cubic-foot chamber, a standard pollutant (like smoke) is introduced, and the device is turned on to its highest setting. Sensors measure how quickly the concentration of particles drops. The result is a number that essentially reflects two things: the efficiency of the filter and, most importantly, the power of the fan.

A powerful fan that moves a massive volume of air through a reasonably good filter will almost always achieve a high CADR score. The entire system is optimized for the rapid, physical removal of particles. For a technology like HEPA, which is a physical filter, this metric is a perfect fit. It directly measures what the device is designed to do.

The Problem with New Philosophies

The trouble begins when a new technology enters the scene with a completely different goal. Photocatalytic oxidation (PCO) and its branded variant, PECO, are not primarily designed for the speed of particle removal. They are designed for the thoroughness of molecular destruction.

As we’ve explored, the effectiveness of this chemical reaction hinges on residence time—how long a pollutant molecule is exposed to the UV-energized catalyst. To effectively break down a complex VOC molecule or neutralize a virus, you need a certain amount of contact time. There is an inherent tension between moving air quickly (to get a high CADR) and moving it slowly enough for a chemical reaction to complete.

This creates a “metric mismatch.” Judging a PECO purifier by its CADR score is like judging a master chef’s meal by how fast it was cooked. You’re measuring the wrong thing. A device could be exceptionally effective at eliminating formaldehyde but score poorly on the CADR test because its fan speed is intentionally moderated to maximize residence time. This mismatch has been at the center of the controversy surrounding Molekule, as its devices often post lower CADR numbers than similarly priced HEPA units, leading to accusations of underperformance from those who view CADR as the only meaningful metric.

What CADR Doesn’t Measure

The limitations of CADR extend beyond the PECO debate. The standard test does not measure a purifier’s ability to:

• Remove Gaseous Pollutants: The CADR test uses only solid particles. It tells you nothing about a device’s effectiveness against VOCs like formaldehyde or odors.
• Neutralize Microorganisms: It measures the removal of particles, but it doesn’t assess whether a trapped bacterium or virus is alive or dead.
• Perform at Lower, Quieter Speeds: The test is conducted at the highest, often loudest, fan speed. It doesn’t reflect real-world performance where users run devices on lower settings, especially at night.
• Sustain Performance Over Time: CADR is a “day one” test. It doesn’t show how performance might degrade as a filter loads up with pollutants.

The Search for a New Standard

So, what’s the alternative? The industry needs a more holistic approach to performance measurement. A future standard might include separate metrics for different tasks:

• Particulate Removal Rate (PRR): Essentially, the current CADR for dust, smoke, and pollen.
• Gas Removal Rate (GRR): A standardized test measuring the removal of a cocktail of common VOCs.
• Bio-inactivation Rate (BIR): A metric to quantify the destruction or neutralization of airborne viruses and bacteria.
• Quiet-Mode Performance: A rating that reflects efficiency at a more realistic, lower noise level.

Until such a standard exists, consumers must become more sophisticated in their evaluations. Instead of asking “What’s the CADR?”, we need to ask a series of more precise questions: “What is my primary air quality problem—particles or gases?” “What technology is best suited for that problem?” and “Is there any third-party data to validate this product’s performance against my specific concern?”

CADR is not a useless metric; it remains a valid measurement for the specific task of rapid particle removal. But it is no longer the only number that matters. The air we need to clean is more complex than just dust and pollen, and the metrics we use to judge our tools must evolve to reflect that new reality.