Decoding Clean Air: A Practical Guide to Air Purifier Metrics (CADR, ACH, and More)

An air purifier’s specification sheet can feel like an alphabet soup of acronyms: CADR, HEPA, CARB, CFM. These technical terms are often buried in marketing language, making it difficult to compare products or even understand what you’re buying. But hidden within this data is the objective truth about a machine’s performance.

This guide will demystify these metrics. We will dissect a spec sheet, transforming confusing jargon into practical tools for your decision-making. By the end, you’ll be able to evaluate any air purifier like an engineer, ensuring you choose a unit that is not just well-marketed, but right-sized and effective for your space. We will use the popular Levoit Core 300 as our real-world case study.

The Engine: Understanding CADR (Clean Air Delivery Rate)

Forget the advertised square footage for a moment. The single most important performance metric on any air purifier spec sheet is its CADR, or Clean Air Delivery Rate. Think of CADR as the purifier’s “horsepower.” It measures the volume of filtered air the machine can deliver in one minute, typically expressed in Cubic Feet per Minute (CFM). The higher the CADR, the faster it can clean a room.

The Levoit Core 300, for example, has a CADR of 141 CFM. This number tells you its raw air-moving and filtering capability. You will often see three separate CADR numbers for Smoke, Dust, and Pollen. Because smoke particles are the smallest and hardest to capture, the Smoke CADR is often the most telling indicator of a filter’s overall efficiency. A high Smoke CADR suggests the purifier is effective across a wide range of particle sizes.

The Real-World Goal: Calculating ACH (Air Changes per Hour)

A powerful engine (high CADR) is useless if you’re using it in the wrong-sized space. This is where our next metric, ACH (Air Changes per Hour), becomes critical. ACH tells you how many times the purifier can clean the entire volume of air in your specific room in one hour. This is the metric that truly determines real-world effectiveness for health and comfort.

Here is the simple formula to calculate it:

ACH = (CADR in CFM × 60) / (Room Volume in Cubic Feet)
(Where Room Volume = Room Length × Room Width × Ceiling Height)

Let’s apply this to a common scenario. Imagine a 12 ft by 15 ft bedroom (180 sq ft) with a standard 8 ft ceiling. The room volume is 12 × 15 × 8 = 1440 cubic feet. Using the Core 300’s 141 CADR:

ACH = (141 × 60) / 1440
ACH = 8460 / 1440
ACH ≈ 5.9

This result is highly informative. It means the Core 300 can exchange all the air in this typical bedroom with freshly filtered air almost six times every hour. For allergy or asthma sufferers, health organizations like ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) often recommend a minimum of 4-5 ACH. Our calculation shows that for this room size, the Core 300 comfortably exceeds that recommendation.

The Quality Standard: What HEPA and Micron Ratings Mean

Now that we know how much air is being cleaned and how often, we need to be certain of how well it’s being cleaned. This brings us to the quality benchmark at the heart of filtration: the True HEPA standard.

The standard dictates that a filter must capture 99.97% of airborne particles down to 0.3 microns in size. To put that in perspective, a human hair is about 50-70 microns thick. A pollen grain is 10-20 microns. The PM2.5 pollution particles that pose significant health risks are 2.5 microns or less. The 0.3-micron standard is crucial because this particle size (known as the Most Penetrating Particle Size or MPPS) is the most difficult for filters to capture. By proving its effectiveness at this hardest-to-catch size, a HEPA filter guarantees high performance across the entire spectrum of common pollutants.

The Trust Seals: Certifications That Matter

Finally, a spec sheet lists certifications. These aren’t marketing fluff; they are independent verifications of a product’s safety and performance.

• CARB (California Air Resources Board) Certified: This is one of the most important certifications. It guarantees the air purifier does not produce harmful levels of ozone. Some purification technologies, like certain types of ionizers, can release ozone as a byproduct, which is a lung irritant. A CARB certification means the device is safe to operate continuously in your home.
• ENERGY STAR Verified: This seal indicates high energy efficiency. It’s a ratio of the purifier’s CADR to its power consumption (watts). An ENERGY STAR unit will perform its job with a lower impact on your electricity bill, saving you money over its lifetime.
• ETL Listed: This is a product safety certification from a Nationally Recognized Testing Laboratory. It means the unit has been tested and meets North American safety standards, ensuring it is not a fire or electrical shock hazard.
  

Conclusion: From Confused Consumer to Empowered Expert

The acronyms on an air purifier’s spec sheet are not there to confuse you; they are there to inform you. By understanding these key metrics, you can cut through the marketing noise and assess a product on its merits. You now have the tools to evaluate a purifier’s raw power (CADR), calculate its real-world effectiveness in your own home (ACH), verify its filtration quality (HEPA), and confirm its safety and efficiency (Certifications). The goal is no longer to find the vaguely defined “best” air purifier, but to find the verifiably “right-sized” and effective purifier for your specific needs.