What is Clean Air Delivery Rate (CADR)?
The Clean Air Delivery Rate (CADR) is an objective metric established by the Association of Home Appliance Manufacturers (AHAM) under the ANSI/AHAM AC-1 testing standard. CADR measures the volume of clean, particle-free air that a portable air cleaner delivers into a room per minute, expressed in cubic feet per minute (CFM).
The Three Particulate Test Pollutants
AHAM tests air purifiers inside a standardized sealed chamber against three specific particle size distributions:
- Tobacco Smoke CADR (0.09 to 1.0 microns): Represents fine wildfire smoke, viral aerosols, and combustion soot. This is the most stringent test because sub-micron particles are the most difficult to capture.
- Dust CADR (0.5 to 3.0 microns): Represents fine mineral dust, pulverized debris, and mold spores.
- Pollen CADR (5.0 to 11.0 microns): Represents coarse airborne plant pollens, textile fibers, and large pet dander.
The AHAM 2/3 Sizing Rule
AHAM guidelines provide a simple formula for room sizing based on Smoke CADR:
Minimum Smoke CADR (CFM) = Room Floor Area (sq ft) × 2 ÷ 3
For example, a 300 square foot living room requires an air purifier with a certified Smoke CADR of at least 200 CFM. This standard guarantees approximately 4.8 air changes per hour (ACH)—filtering the entire volume of room air every 12.5 minutes.
Why Fan Speed Matters for CADR
Certified CADR numbers are always recorded at the unit's maximum fan speed. When you run an air purifier on low or sleep mode to reduce acoustic noise, airflow delivery drops by 60% to 75%. If you plan to operate a purifier quietly in a bedroom, choose a unit rated for a significantly larger room so that its medium or low setting provides sufficient CADR.