Air Purifier CADR-ACH-SQFT Reference

The values in the table below indicate the square foot coverage corresponding to Clear Air Delivery Rate (CADR) and Air Changes Per Hour (ACH). These numbers represent a 100% efficiency system where the CADR is equivalent to Cubic Feet Per Minute (CFM), and assumes nominal 8 ft. ceilings.

Here are a few important notes for you when you are looking at CADR, which is tested and rated for larger air particles such as dust, pollen and smoke only.

A high CADR rating won’t tell you if the unit removes small particles (e.g. mold, gas/VOCs, bacteria, viruses and etc.).
Some units score high in removing larger particles, but perform poorly in removing smaller particles. In many cases, these smaller particles contribute to your allergies, asthma or other respiratory issues.
A high CADR rating won't tell you how well the unit will perform over time. Some will wear quicker over time than others.
CADR testing is done with the highest fan speed when noise level is at maximum. In reality, most run their units in lower fan speed with quieter operation. That means the room coverage is less than what is advertised.
CADR doesn't really measure how clean the air is coming out of the unit.
For example, a 200 CFM unit running at 50% efficiency and a 100 CFM unit running at 100% efficiency both have a CADR of 100. However, the 100% efficiency unit produces cleaner air.

If you are considering a traditional HEPA/Carbon technology and have the budget, we highly recommend you choose an air purifier with a TRUE HEPA or Medical-Grade HEPA filter.

Now for some calculations. Assume the following as an example:

ACH = 2, CADR = 400

Per the table, the square footage = 1500 (assuming 8 ft. ceiling height)

CADR = [(ACH x L x W x H) / 60] CFM * Efficiency

Doing the math we have:

400 = (2 * 1500 * 8) / 60

CADR	ACH1 SqFt	ACH2 SqFt	ACH3 SqFt	ACH4 SqFt
100	750	375	250	188
150	1125	563	375	250
200	1500	750	500	375
250	1875	938	625	469
300	2250	1125	750	563
350	2625	1313	875	656
400	3000	1500	1000	750
450	3375	1688	1125	844
500	3750	1876	1250	938