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.
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