Why Air Purifier Specs Are So Confusing

Air purifier marketing tends to be heavy on impressive-sounding numbers and light on context. "Removes 99.97% of particles!" sounds great — until you realize that's only true for particles of a very specific size, under lab conditions, not your actual room. This guide cuts through the jargon so you can compare products on terms that actually matter.

The Specs That Actually Matter

CADR (Clean Air Delivery Rate)

CADR is the most useful single number when comparing air purifiers. It measures how much clean air (in cubic feet per minute) a purifier delivers, tested independently by AHAM (Association of Home Appliance Manufacturers). Higher is better.

CADR scores are given for three pollutant types:

  • Smoke (fine particles, 0.1–1 micron)
  • Dust (medium particles, 0.5–3 microns)
  • Pollen (large particles, 5–11 microns)

A quick rule of thumb: your CADR for smoke should be at least two-thirds of your room's square footage. For a 300 sq ft room, aim for a smoke CADR of 200+.

ACH (Air Changes Per Hour)

ACH tells you how many times per hour the purifier cycles all the air in a given room. For general use, 4–5 ACH is the target. For allergy sufferers or people with respiratory concerns, aim for 5+ ACH.

To calculate: (CADR × 60) ÷ room volume in cubic feet = ACH. Most manufacturers publish room size recommendations — verify they're based on 4+ ACH, not 2.

Filter Type: True HEPA vs. Everything Else

True HEPA filters must capture at least 99.97% of particles at 0.3 microns — the hardest size to trap. This is the standard you want for dust, pollen, mold spores, pet dander, and many bacteria.

Watch out for these misleading alternatives:

  • "HEPA-type" or "HEPA-like": No defined standard, significantly less effective
  • "HEPA-style": Same issue — marketing language, not a certification
  • Ionizers/plasma: Can produce ozone; less effective at particle removal

Activated Carbon Filter

HEPA filters don't capture gases, odors, or VOCs (volatile organic compounds from paint, cleaning products, furniture). For those, you need an activated carbon layer. Look for purifiers with a substantial carbon filter — thin carbon meshes on cheap models provide minimal benefit. This matters most if you're dealing with cooking smells, smoke odors, or off-gassing from new furniture.

Features Worth Paying For

  • Auto mode with air quality sensor: Adjusts fan speed based on real-time particle readings. Genuinely useful and extends filter life.
  • Filter replacement indicator: Takes the guesswork out of maintenance.
  • Low noise at high settings: Measured in dB. Anything above 55 dB on max is noticeable. Look for units that achieve good CADR at mid-fan settings.
  • Energy efficiency: Purifiers run continuously. Look for Energy Star certification and check annual running cost estimates.

Features You Can Skip

  • UV-C lights: Minimal proven benefit in consumer units at typical exposure times.
  • Wi-Fi/app control: Nice to have, not necessary.
  • Air quality displays: Useful only if the sensor is high quality — cheaper sensors are unreliable.

What to Budget

Room Size Recommended CADR Typical Price Range
Small (up to 200 sq ft) 130+ $60–$120
Medium (200–400 sq ft) 200–260 $100–$200
Large (400–700 sq ft) 300–400 $180–$350

Don't Forget Filter Replacement Costs

Factor in the annual cost of replacement filters when comparing models. Some purifiers have low upfront prices but expensive proprietary filters. A $150 purifier with $80/year in filters is more expensive long-term than a $200 purifier with $40/year in filters.