Air Purifier Terms: Your Complete Glossary

For people who are just getting into the world of air purifiers, the terms used can sometimes seem confusing. When discussing contaminants, air purifier features and other aspects of air purification, specialized vocabulary is often used. To help you make sense of the jargon, we’ve put together this glossary of air purifier terms that you’ll frequently see used in descriptions and manufacturers’ ratings.


Why Is it Important to Know These Terms?


When you’re getting ready to buy an air purifier, there are several different metrics and features you’ll need to understand to make the right choice. If you don’t know what you’re looking at, there’s a good chance you’ll accidentally select an air purifier that isn’t right for your home and your needs. To make the most informed buying decision, it’s important that you speak the same language as the air purifier manufacturers that write the specifications.


Keep in mind that buying the wrong air purifier isn’t just a waste of time and money. If you select a unit that doesn’t properly cover your home, you could be leaving yourself and your family exposed to contaminants that a better-suited purifier would be removing. With such high stakes, we think it’s important that you be able to easily navigate all of the ratings, specifications and features each air purifier has to offer.




Following, you’ll find the most important air purifier terms arranged in alphabetical order. To help expand on some of these concepts, we’ll also include links to blog posts we’ve written about specific topics and relevant product examples from time to time.

Activated Carbon


A filtering material used to capture gases, odors and chemicals. Activated carbon is chemically treated to allow it to capture airborne gases. Activated carbon filters often take the form of large drums weighing several pounds, with a greater volume of carbon corresponding to greater filtration capabilities. The Airpura C600, for example, uses a 26-pound carbon canister to efficiently remove airborne chemicals. Some activated carbon is treated with chemical adsorbents to help it remove VOCs and gases more effectively. This type of carbon is known as impregnated carbon.


AHAM Certification


The Association of Home Appliance Manufacturers (AHAM) conducts independent testing to certify the clean air delivery rate (CADR) of different air purifiers. Manufacturers pursue AHAM certification voluntarily by allowing their units to be tested and rated.


Air Changes Per Hour (ACH)


The number of times an air purifier can cycle through the air in a given space in one hour. The higher this rating is, the more frequently the unit can completely clean the air. The Blueair Pro L, for instance, executes five air changes per hour in spaces of up to 1,180 square feet. ACH is calculated by manufacturers under ideal conditions, and a wide range of factors can reduce the actual frequency of air cycling in real-world use. Typically, manufacturers calculate ACH without a filter in the machine, resulting in a “free flowing” measurement instead of a true delivered ACH rating. ACH ratings can be helpful, but it’s important to keep in mind that the real rate of air cycling will be a bit lower than the manufacturer’s rating.


Air Quality


A measure of the overall level of pollution or contaminants in the air at one time. This is usually measured using the air quality index, or AQI. The AQI ranges from 0 to 500, with larger numbers representing higher pollution levels. The AQI measures particulates, ozone, carbon monoxide, nitrogen dioxide and sulfur monoxide. It should be noted that there are several different indices for measuring air quality. If you live in a country other than the United States, your local standard may be different than the AQI.


Air Quality Meter


An air purifier accessory that measures the overall quality of your indoor air. Air quality meters can help you see how well your air purifier is performing and give you hard numbers to work with in improving the health of your home air. For more information, see our selection of indoor air quality meters. The Foobot meter, for instance, is great for measuring total VOCs and particulates in your home.



Wheels that can be found on the bottom of most larger air purifiers. Because air purifiers are typically a bit heavy, casters make them much easier to move from room to room as needed.


Clean Air Delivery Rate (CADR)


A rating given by the AHAM to air purifiers on the basis of their ability to filter various contaminants from the air. The CADR scale measures the speed at which air purifiers remove dust, tobacco smoke and pollen. The higher the CADR rating, the faster a given unit eliminates that contaminant. To learn more about CADR, visit our page on AHAM certification and CADR ratings.


Coverage (Capacity)


The amount of space an air purifier is designed to cover, sometimes also referred to as capacity. Coverage is expressed in square feet and is calculated assuming a standard 8-foot ceiling. To learn more, check out our blog post on how air purifier capacity is calculated and how to adjust it for spaces with difference ceiling heights.


  Cubic Feet Per Minute (CFM)


A measurement of the volume of air an air purifier can cycle through each minute. The higher the CFM rating, the faster the air purifier is drawing air in. As with air changes per hour, CFM ratings are generated by manufacturers under ideal conditions. While the rating can be useful in determining which air purifier is right for you, it should be treated more as a general guideline than a hard and fast measurement of an air purifier’s real-world performance.


Energy Star


Energy Star certified air purifiers are those that are the most energy efficient. Energy Star is a government program that provides efficiency ratings for many household appliances in an effort to help consumers reduce their carbon footprints.


Fan Speed


A setting that allows users to increase or decrease the speed of an air purifier’s fan. The higher the fan speed, the more air the machine will be able to process. However, higher fan speeds also increase noise levels to some extent, and a higher fan speed will also somewhat increase power consuption.


Filter Change Indicator


A feature that reminds users when an air purifier is due for a change. Generally, this takes the form of an indicator light or a reminder displayed on the unit’s control panel. Keeping up with regular filter changes is an important part of keeping your air purifier working at maximum capacity.


Filterless Air Purifier


Any air purifier that uses a method other than a filter to clean the air. Typically, filterless air purifiers use heat to destroy particles in the air, as is the case with the Airfree line of air purifiers. While filterless purifiers provide good protection against particles, they have no ability to capture gases or odors.




A type of filter used for particles. To meet HEPA standards, a filter must capture 99.97 percent of particles more than 3 microns in diameter. HEPA filters are the best way to capture dust, dander, pollen, mold spores, particulate matter and other ultrafine contaminants.


Noise Level


A measurement of the volume of noise produced by an air purifier. This measurement is given in decibels and can help you determine how loud an air purifier will be. Keep in mind that noise level will vary with fan speed, and many manufacturers give individual noise level ratings for each fan speed setting. If you’re looking for low-noise air purifiers, check out our blog post about the 6 best quiet HEPA air purifiers.





A molecule made up of three oxygen atoms. While some people believe that ozone is good for air quality, it is actually a dangerous chemical when inhaled. For maximum health benefit, a good air purifier must be ozone-free. Our readers are encouraged to avoid so-called ozone generators at all costs. These machines may be promoted as air cleaners, but the ozone they introduce into your home air is at least as dangerous as any normal contaminant.




A layer of material through which air passes before reaching an air purifier’s main filter. Prefilters are meant to catch large debris, such as pet hair and larger dust particles. Many prefilters are washable and can be reused several times before needing to be replaced.


Power Consumption


A measure of how many watts of power an air purifier draws while running. Most air purifiers these days are reasonably energy efficient, though power consumption can vary widely from model to model. For more information of wattage, check out our blog post about how much electricity air purifiers use.


  UV Germicidal Lamp


An ultraviolet lamp added to some air purifiers to target bacteria and viruses. The application of UV light to these common contaminants renders them neutral, resulting in healthier home air. Ultraviolet light has the ability to disrupt the DNA of bacteria and viruses, ultimately killing them and preventing them from multiplying. It’s important to keep in mind that UV lamps must be changed on a regular basis just like filters. Even if a lamp is still glowing after a year of use, it will have lost a significant amount of its germicidal capabilities. For more information about units equipped with this feature, see our blog post about the best UV air purifiers.


Volatile Organic Compound (VOC)


A class of organic compounds that vaporize easily at or near room temperature. VOCs include toxic gases that can cause severe health problems in humans when inhaled. To remove VOCs, an air purifier with an activated carbon filter is needed. Common VOCs include formaldehyde, benzene and tetrachloroethlyene (TCE). Because these chemicals are sometimes used to treat construction materials, VOCs are often present in small amounts in home air. Depending on the VOC in question, specially impregnated carbon may be required to remove it.


  Wall Mount


A class of air purifiers that can be mounted on walls instead of left sitting on floors. Wall-mountable air purifiers are useful when floor space is limited, making them great for small bedrooms, offices, studio apartments and other small spaces. For more information, see our blog post about the best wall-mounted air purifiers.


Is This Everything You Need to Know About Air Purifiers?


While knowing these terms is a great starting point, there are still other things you will need to know to make an informed buying decision. For a more thorough rundown of key concepts and buying factors, be sure to check out our air purifier buying guide and FAQ page. You can also use our blog as a learning resource, as we’ve created hundreds of articles on air purifiers, features, uses and various contaminants over the years!


Now that you’re familiar with these terms, though, you should be able to navigate manufacturers’ ratings and descriptions with no difficulties. Still have questions? Don’t worry, we’re here to help! Feel free to contact us with your questions, and we’ll be happy to provide you with answers and personalized product recommendations based on your unique needs.