CADR Rating: Is it a Good Measure of Air Purifier Quality?

One of the most common metrics by which air purifiers are measured is the clean air delivery rate, or CADR rating. Many first time buyers treat CADR as a proxy for air purifier quality. In this article, we’ll explain what this measurement is, how it works and discuss some of the limitations of using it as your only standard when buying an air purifier.


What Is the CADR Rating?


Before we can look at the pros and cons of CADR, it’s important to first understand what it is and how it’s calculated. CADR metrics are given in three categories: dust, smoke and pollen. In each category, the CADR rating measures how many cubic feet of air a given air purifier effectively removes each type of particle from each minute. The highest possible rating scores are 450 for smoke and pollen, while 400 is the highest score for dust. The higher an air purifier scores in a given category, the more efficient it is at removing particles in that size range.


How Is CADR Calculated?


To calculate CADR, an air purifier is placed in a room measuring 1,008 cubic feet. The air purifier is then allowed to run for 25 minutes. After the 25 minute test, the levels of the three contaminants the test is designed for are measured against the pre-test levels. In this way, an objective measure of how well the purifier removes the different particle sizes can be calculated.


Who Calculates CADR Ratings?


CADR tests are conducted by the Association of Home Appliance Manufacturers (AHAM). To get a CADR for an air purifier, the manufacturer voluntarily submits it to the AHAM for testing. Because the AHAM uses the same test for every air purifier, CADR ratings are fairly consistent and represent a good measure of air purifier efficiency in the tested categories.


Do All Air Purifiers Have a CADR Rating?


While many air purifiers do carry a CADR measurement, the AHAM rating process is entirely voluntary. As a result, you may find some purifiers that have not been tested or assigned a rating. This doesn’t necessarily mean that these units are sub-par air purifiers, but it does make it a bit more difficult to evaluate them.


Benefits of CADR Measurements for Consumers


Now that we’ve taken a look at how CADR ratings work, let’s discuss how they benefit consumers. A CADR allows potential buyers to objectively compare air purifiers when making a purchasing decision. Unlike measurements such as air flow rate and overall capacity, the CADR provides a specific measurement of how well an air purifier does in filtering out particles of different sizes. The objective nature of a CADR rating makes it much easier to tell how well an air purifier will perform when compared with other units that have undergone the same testing.


CADR ratings are also useful because they show you how well an air purifier can remove several common contaminants. If your main aim in using an air purifier is to remove pollen from your home air, for example, you can select a unit that has a high pollen CADR rating but may perform less well when it comes to removing smoke. Thanks to the three-category nature of the test, consumers can select the air purifier that best suits their unique needs.


Finally, the CADR rating introduces a certain amount of transparency into the air purifier rating process. Because it is conducted by a neutral third party under pre-set conditions, the CADR test gives an unbiased measurement of air purifier performance. Other metrics, such as air flow, often represent the air purifier operating under ideal rather than real-world conditions. When you’re looking at a CADR rating, you can at least know that it is generated using a standard test administered by a disinterested party.


What Are the Drawbacks of CADR?


For all of their advantages, CADR ratings don’t tell you everything about an air purifier. One of the biggest CADR limitations is the fact that the test does not include gases, odors or VOCs. These non-particulate contaminants are very common in home air and can be targeted by air purifiers that use carbon filters. Many air purifiers that carry CADR ratings use HEPA as well as carbon filters. When these air purifiers are submitted to the CADR test, only one part of their filtering capabilities is actually being measured. So, if gaseous contaminants are part of your home air quality concerns, a CADR test should not be the only metric you use in picking out an air purifier.


Another drawback of the CADR test is that it only tests air purifiers on their highest settings. While this is an understandable standard for the test, it can inflate the unit’s efficiency in a buyer’s mind. If you are buying a bedroom air purifier, for example, it’s fairly unlikely that you would run it on its highest setting while you’re sleeping due to noise concerns. This being the case, the air purifier you buy would not be performing as efficiently as it was under the conditions of the CADR test. This fact is important to keep in mind when looking at the CADR ratings of air purifiers you’re considering.


Finally, the CADR test only shows how an air purifier will work within a very limited period of time. While the 25-minute test allows the unit to cycle a significant amount of air through, it can’t tell you how it will perform after weeks or months of continuous use. As HEPA filters absorb particles from the air, they naturally experience slight declines in efficiency. While this shouldn’t be a serious problem if you’re changing your filters on the manufacturer’s recommended schedule, it is worth noting that the clean air delivery rate of a purifier with a brand-new filter operating for only 25 minutes will be higher than that of the same purifier with a filter that has been absorbing particles for several months.


How Should You Use the CADR Rating?


Once you understand the advantages and drawbacks of CADR ratings, you can make proper use of them when buying an air purifier. As a rule, CADR is a great thing to consider when looking at particle filtration. The rating will give you a fairly good idea of how a given air purifier will do when it comes to removing dust, smoke and pollen from your home air. If one or all of these contaminants is your main home air quality concern, you should definitely pay attention to the CADR ratings of the units you look at.


With that said, you shouldn’t make your buying decision based solely on CADR. While it’s a useful metric, the rating doesn’t give you any information about gas filtering and doesn’t represent every important aspect of an air purifier. As a result, the best way to approach CADR is as one component of your purchasing decision, rather than the only metric you look at.


What Else Do You Need to Look at When Buying an Air Purifier?


To get the best air purifier for your needs, you should consider several different factors. First and foremost among these is the kind of air purifier you need. As stated above, purifiers with HEPA filters target particles, while those with carbon filters target gases. If you want to filter out both classes of contaminants, you’ll need an air purifier that combines these two filter types. Deciding what contaminants you’re most concerned about and choosing your model accordingly is arguably the most important step in buying an air purifier.


You also need to think about the size of the space your purifier will be used in. As you can imagine, a unit capable of covering a mid-sized house must be able to cycle air much more quickly than a unit that covers a studio apartment. In addition to CADR, you should be looking at the CFM (cubic feet per minute) of air flow and the unit’s square footage rating to determine what unit is best for your needs. Keep in mind that unless stated otherwise, most air purifiers’ square footage ratings are calculated on the basis of one air change per hour in a space with 8-foot ceilings. To learn more about area ratings and how to adjust based on different ceiling heights, check out our blog post on air purifier capacity here.


Another important factor to consider is the physical size of the air purifier itself. Some buyers intend to use their units in areas where floor space may be limited. In these cases, either a small air purifier or a wall-mounted model are usually the best choices.


Likewise, it’s important to consider the noise level you’re comfortable with. Many air purifiers can operate very quietly on their lower fan settings. As stated above, though, lower fan speeds will reduce the functional clean air delivery rate. Try to find a unit that offers a good balance between your noise comfort level and efficient filtering. Ending up with a unit that’s too noisy, even if it means better filtration, can be a serious annoyance and make you less likely to keep using an air purifier over time.


Finally, you should consider the additional features of each air purifier you’re looking at. Some models, for example, offer a convenient filter change reminder light that will tell you when it’s time for new filters. Others, like the Blueair Pro L, can automatically detect air quality levels and change their settings accordingly. Note that in the case of Blueair this is an optional rather than a standard feature.


Monitoring Air Purifier Performance in Real Time


As stated above, the CADR rating will give you a picture of how an air purifier performs only within a 25-minute window and using a brand-new filter. If you want to get a more complete picture of how your air purifier operates over the course of its lifetime, you can monitor its performance yourself using a home air quality meter. These simple, easy-to-use devices let you see the levels of different contaminants in your home so that you can take effective steps to remove them.


When used in conjunction with an air purifier, these monitoring systems become especially valuable tools. You can, for example, try running your air purifier on different fan speeds, then monitor the effects on your indoor air quality using the meter. Likewise, you can see how well your purifier performs as its filters age. With this kind of real-time monitoring, you can always know where your home air quality stands and test the effects of different approaches to improve it.


As you can see, an air purifiers CADR rating is a valuable metric in choosing the right unit for your home, but it shouldn’t be the only thing you think about. Be sure to consider square footage, additional features, CFM ratings, filter types and other factors as well. Picking the right air purifier is often a bit of an involved process, but the results can be well worth the effort.


Still have questions about CADR ratings or the metrics you should use to select an air purifier? We’re here to help! Feel free to send us your questions, and we’ll be happy to provide you with the answers and information you need. If you’re still not sure what air purifier is best for you, we’ll also be happy to provide you with personalized product recommendations based on your needs to help you get the right air purifier the first time.