What is CADR?


Anyone who has been researching air purifiers for an extended period of time has undoubtedly come across the acronym CADR at least once. Most people just gloss over it, figuring that it’s something they can’t understand or don’t care to understand.

But it’s important. Not only that, it’s pretty easy to understand too!

CADR stands for Clean Air Delivery Rate and it is a measure that was made to tell consumers how well an air purifier performed. The CADR rating measures how much air, measured in cubic square feet, an air purifier can filter in a minute.

As I’m sure you’ve already figured out, the larger the CADR the better. More air getting cleaned is always better!

Want to check out some of the best CADR-rated air purifiers? Check out Medify Air’s air purifiers here. Or, if you’d like to shop around several different brands, click here and you’ll be taken to Amazon.

How is the CADR Rating Decided?

The Association of Home Appliance Manufacturers (AHAM) is in charge of the CADR ratings and they randomly select air purifiers to independently test. AHAM has loads of information on their website on their work and recommendations, which makes them a valuable resource for those who want to dive in deep into their research. AHAM shares their methods for checking CADR here, but I’ll be outlining it in this article in fewer words.

Most people have better things to do with their time, hence why you came to me to answer your questions and you didn’t start a 40-hour research project!

CADR is decided by how effectively an air purifier can remove these three particles that are in your home’s air: smoke, pollen, and dust. These three particles are great measures for the effectiveness of an air purifier because they represent small, medium, and large particle sizes respectively. Additionally, they are each given their own CADR score, since they’re different sizes.

The testing process for CADR is tedious and technical. It’s full of cool science and math equations and it’s, again, super technical, so I won’t dive too deep on that. This article is for the casual consumer, not someone who wants to spend a wad of cash to run the test everything themselves.

On the left (or above, depending on the device you’re looking at) I have a little diagram of what’s happening when the air purifier is tested. On the left is the dirty air and on the right is the clean air. The filter (the blue box in the middle) captures the particles.

Now, CADR is a rating that checks the efficiency and the airflow (measured in CFM) of an air purifier. The equation they use is essentially airflow times efficiency.

So, say this air purifier in my little diagram had an airflow of 500 CFM (which is pretty high), then we need to decide its efficiency. As you can see in the picture, one particle made it through, so it is not 100% effective against the particle it’s being testing for (remember, it’s tested for three particles, smoke, pollen, and dust).

For ease of calculations, let’s say that the particle that got through lowered the efficiency to 90%. That means that we need to multiply 500 by 90 percent. Once you do that, you get a CADR rating of 450.

Air purifier manufacturers can’t fib and can’t mislead people with the CADR rating like some try to do with HEPA filters. (Some say a filter is “HEPA type” which does NOT make it a HEPA filter. It does, however, trick some people into buying the air purifier thinking it’s got a HEPA filter.) Essentially, the CADR rating is a great measure to buy your air purifier with.

Want to check out some of the best CADR-rated air purifiers? Check out Medify Air’s air purifiers here. Or, if you’d like to shop around several different brands, click here and you’ll be taken to Amazon.

How Can I Get the Most Out of My Air Purifier?

To get the most out of your air purifier, and to see it cleaning the air up to its CADR rating, you need to operate your air purifier like it was when it was being tested. To do so, run your air purifier on its highest setting, with clean filters.

That’s it, it’s really that simple. But I know that that’s a little lame, so I’ll dive in deeper below and answer a few questions that you might have.

Operate Your Air Purifier on its Highest Setting for the Cleanest Air

it has, you need to run it on its highest setting. Why? Because that’s what the CADR rating is taken from. Air purifiers are tested on their top fan speed.

Why won’t a lower fan speed clean the air as well?

Well, a lower fan speed will still clean the air just as well as the top speed (or possibly better), but it comes at a cost: less air is being cleaned. Remember how the CADR involves the efficiency of the air purifier and its airflow rate? A lower fan speed lowers the airflow since it can’t pull air in as quickly.

For easy numbers, let’s look at it this way: an air purifier at its top speed runs 100 cubic feet of air through it a minute. On its medium speed, that number drops to 50 cubic feet–that’s a 50% drop! And finally, on its lowest setting, it’ll circulate just 25 cubic feet per minute, that’s 75% less than the highest setting.

Now, those numbers are made up, but I hope it illustrated my point, lower fan speeds lower the amount of air that’s circulated and it will lower the effective CADR that you’ll be able to notice (because, again, CADR revolves around airflow).

Operate Your Air Purifier With Clean Filters to Get the Cleanest Air

Clean filters are important for several reasons. For starters, a dirty filter could actually make your air dirtier when the stuff in it is blown out and into your home’s air. In addition to that, your air purifier’s airflow will be negatively impacted by the dirty, clogged-up filter.

To illustrate this point, I made a little picture of a clogged pipe and a clean one. To make it look yummier, I made the clog green.

Now, I’m sure you can tell which pipe is clean and which one isn’t. In addition to that, I’m sure you’re able to guess which one will let more water through it.

Obviously, a clean pipe allows more stuff through it, that’s why they don’t sell dirty pipes in stores. You don’t want something that’s already full and won’t let anything through.

In addition to a dirty pipe clogging up and slowing things down, there’s the risk of them making everything that passes through dirty as well. That’ll get you dirty, yucky water.

Now tell me, why would you expect an air purifier to work any different?

Obviously, a dirty filter will limit the flow going through it and it will obviously have the risk of giving you dirty air, just like a dirty pipe would give you dirty water.

The CADR testing uses a clean filter and that clean filter will do the best at cleaning the air and it will do the best at allowing the most airflow through. As I’m sure I’ve proven to you by now, CADR requires efficient air cleaning and good airflow, and a clean filter is a must for that.

But wait! Don’t replace your filter every five minutes!

Air filters are supposed to be replaced, yes, and dirty ones won’t work as well, but you don’t need to replace your filters all the time. Most HEPA filters just need replaced every 6 to 8 months (ish). The manufacturers test their filters and they run the numbers to see how long your filter can last before it’s too clogged up to work well. It’s different between every air purifier, so keep that in mind, but it won’t be every five minutes!

Want to check out some of the best CADR-rated air purifiers? Check out Medify Air’s air purifiers here. Or, if you’d like to shop around several different brands, click here and you’ll be taken to Amazon.

Can I Trust the CADR Rating on My Air Purifier?

The ANSI/AHAM AC-1 CADR is widely accepted, and has become more and more accepted since its conception. Air purifiers that claim CADR ratings are tested periodically to ensure their compliance. In addition to being an industry standard, CADR testing is updated when the need arises as well to ensure everything is as good as it can be.

Ever since the establishment of the CADR rating back in the early 1980s, manufactures have had to ensure that their air purifiers meet the CADR levels that they claim their machines can clean the air at. If they don’t, then they’ll be in trouble with AHAM, and that’s not good for them! Long story short, you should be able to trust the CADR ratings that they list.

While AHAM doesn’t test every air purifier as it’s released, they do randomly select air purifiers to ensure overall compliance. One big reason why they don’t check every air purifier is because so many are made; it’d be impossible to keep up!

On top of that, the random tests (which are conducted by independent testers) check air purifiers that have been on the market for years as well. Why? Well, it ensures that every air purifier remains up to the CADR rating that it claims to have, no matter how long it’s been made. That means that no one can make a good air purifier at the start to sneak through and then make bad air purifiers after it passes. Every air purifier is the best it can be, thanks to AHAM’s periodic random CADR testing.

That’s all I’ve got for today, but feel free to poke around my site to find whatever other article piques your interest. And, if you haven’t picked up an air purifier just yet, then you can buy some from Medify here and, if you’re in the market for a few air purifiers, you can save some money by buying a bundle here. Or, if you’re curious about how clean the air in your home is, then you can buy radon detectors and other air monitors for your home from Airthings here. Use the code ape10-10off to get 10% off your order.

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Jonathon Silva

Jonathan Silva is our longtime Air Purifier Essentials author. He has been writing on air purification technologies for his entire professional career.

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