Understanding CADR and how it relates to room size

CADR stands for Clean Air Delivery Rate. This rating was invented by the Association of Home Appliance Manufacturers, and today, it remains the most accurate metric for measuring an air purifier’s efficacy. This numerical value will tell you exactly what quantity of particulate matter the purifier will remove from the air. 

Broadly speaking, CADR rating indicates the power of the fan or indicates how fast it can clean the air within a particular space. The CADR rating is measured in CFM, which stands for cubic feet per minute. For example, an air purifier with a CADR rating of 300 CFM will clean a room of 300ft2 much faster than an air purifier with a CADR rating of 200 CFM.

Calculating square footage and other variables

Therefore, knowing the size of the space the air purifier needs to service is important when selecting your unit. Ideally, you should choose an air purifier that delivers between two and five air changes per hour, or every 12 to 30 minutes. Naturally, the size and power of your purifier will depend on the overall dimensions of the room. Smaller rooms need less power than larger spaces, so make sure you have accurate measurements before you start shopping around.

Calculating the size of the space is perfectly straightforward, so long as you keep some basic but easily overlooked things in mind. First, make sure you get help from a friend or colleague to ensure the measurements are accurate. Next, measure the length and width of the space in feet and inches (not metres and centimetres!) so as to comply with the CADR calculation.

Multiply these two numbers together and you have the basic square footage of your room, and thus, a benchmark for the efficacy of your chosen unit. However, you also need to take into account the room’s ceiling height. If the ceilings are above an 8-foot average, then the CADR will be lower than the rating indicated by the manufacturer.

For example, if your room is 100ft2 and the ceilings are 8 feet high, the volume of air in the room is 800 cubic feet. With 10 ft high ceilings, this increases to 1,000 cubic feet or 25% more. Therefore, you’ll have to take 25% off of the stated efficacy of the air purifier.

A final note on your calculations

Finally, you need to take into account that the CADR is based on the maximum fan speed of the air purifier. If you’re trying to save energy, it’s likely that you’ll want to run the purifier at a lower setting – this will also reduce noise, too. When you do this, the coverage will decrease. Therefore, it might be advisable to purchase a more powerful purifier than you think you might need.

You also need to bear in mind that CADR ratings are only relevant to particular contaminants, namely dust, pollen and smoke. If you need an air purifier for a specific kind of virus or bacteria, then the AHAM’s CADR ratings don’t apply. It’s for this reason that Rejuvenair’s units are so much more than fan-powered purifiers.