White Paper
CADR measures the reduction of the three most common indoor air
pollutants at home: smoke, dust and pollen. These three pollutants
represent different sizes of particles with pollen being large sized
pollutants, dust medium and smoke small. The unit for CADR is cu-
bic feet per minute (cfm) which tells us that the higher the numbers
are, the faster the unit cleans the air in the room.
11
CADR test standard, called ANSI/AHAM AC-1-2006, is the only
air cleaner standard that is recognized as an American national
standard. It has been developed by the Association of Home Appli-
ance Manufacturer (AHAM), an organization that oversee standards,
testing and verifications for air cleaners together with other appli-
ances. AHAM is an independent organization, which ensures that
the testing results are accurate and impartial.
12
How to estimate the CADR of unrated air cleaners
CADR are rated within the range of 10 to 450 cfm for tobacco
smoke, 10 to 400 cfm for dust and 25 to 450 cfm for pollen. These
numbers are tested and certified on air purifiers by AHAM. The
membership of AHAM and its CADR programme is voluntary which
makes it difficult to know how to compare products that are not
tested and certified. But CADR could easily be estimated by the
following procedure:
Find out specifications for efficiency and airflow of the air purifier. 1.
Efficiency represents the proportion of pollutants removed (%)
and airflow represents the volume of air that passes through the
unit per time unit (cfm).
With the formula below you can estimate the CADR of the unit.2.
CADR = [filter efficiency at 0.3 µm] ] x [airflow in CFM]
An air purifier with low filtration efficiency can have the same or even
higher CADR than an air purifier with higher filtration efficiency. As an
example, we have two units with following specification:
Unit 1: Efficiency = 99.97%, Airflow = 125 cfm
Unit 2: Efficiency = 80%, Airflow= 250 cfm
The estimated CADR for the two units will then be:
Unit 1: 99.97% x 125 cfm ≈ 125 cfm
Unit 2: 80% x 250 cfm = 200 cfm
As can be seen from this example, a unit with lower filtration ef-
ficiency can have better performance compared to a unit with high
filtration efficiency, giving the conclusion that for high performance, a
unit must have both high airflow and good filtration efficiency.
What CADR do you need?
AHAM guidelines helps to determine which CADR a specific room
size need. One simple way to calculate needed CADR is the 2/3
Rule. The 2/3 Rule means that the air purifier should have a CADR
for tobacco smoke equal to 2/3 of the room’s floor area. So saying
that a room has an area of 120 sq. ft., the CADR for tobacco smoke
should be:
120 x 2/3 = 80 cfm
7. Solution
When choosing an air cleaner, performance should be considered first. A unit’s pollutant
removal performance is best shown with its Clean Air Delivery Rate (CADR), a standard-
ized measurement system developed in the USA by the independent Association of
Home Appliance Manufacturers (AHAM) that helps to determine an air cleaner’s efficiency
in removing pollutants from the air.
11
http://www.cadr.org/consumer.htm
12
http://www.aham.org/consumer/ht/d/sp/i/1074/pid/1074