Learn the ABCs of IAQ and How to Select an Air Purifier

Learn the ABCs of IAQ and How to Select an Air Purifier


Buying an air purifier shouldn’t be complicated, but at times it feels like wading through a sea of abbreviations and acronyms. Let's tackle the terms and why they matter.

 PM, AQI and IAQ are used to identify, index, and measure particle pollution.

PM or particulate matter is measured in microns. PM2.5 (smaller than 2.5 microns) and PM10 (smaller than 10 microns) are harmful to human health, as they can enter the respiratory system, the lungs, and the blood stream. Both are associated with higher levels of lung disease, heart disease, cancers, and dementia. Read more on particles and health here.

 AQI stands for Air Quality Index and is the Environmental Protection Agency's gauge for measuring outdoor air pollution, with a range from 0 to 500; The higher the AQI value, the greater the air pollution and related health concerns. An AQI of 50 or lower is considered good. The important thing to know about AQI is that it affects your indoor air quality as well because air is exchanged between outside and inside. Particulate matter (including PM 2.5 and PM 10) is one of five pollutants measured by the AQI. To learn more about the AQI and to see the real-time air quality in your zip code visit airnow.gov. Wildfires significantly affect air quality even thousands of miles away. See smoke plume dangers at airnow.gov too.

IAQ is short for Indoor Air Quality. Every home, office, and indoor space has one. And it can change dramatically depending on what you are doing. The best way to find out your IAQ? Invest in a high-quality IAQ monitor. There are a wide range of options depending on budget and specific concerns. Check Wirecutter.com, the reviews site from the New York Times, for suggestions.  

 A standalone IAQ monitor may be more reliable than the monitor found on portable air purifiers, as these only measures air quality at the air purifier location.

CADR, CFM, ACH, and CCM all relate to air purifier performance

CADR  If you’ve started shopping for an air purifier, you’ve probably seen CADR, or Clean Air Delivery Rate mentioned. CADR is an industry standard, set by the Association of Home Appliance Manufacturers (AHAM), to compare the cleaning power of between new air purifiers. Independent testing labs conduct CADR tests following a strict protocol to meet AHAM standards. 

What does CADR measure?

Measured in cubic feet per minute (CFM), CADR is the air purifier’s contribution of clean air added to the room. For any set room area, an air purifier with a higher CADR can remove particles more quickly than a lower-CADR air purifier. Three distinct particle pollutant sizes are measured in CADR tests: smoke, dust, and pollen. You will see different results for each, in a range from 0 to 450.

Are CADR and CFM the same thing? No, and you don't want to assume CFM=CADR. It can be confusing because CADR is measured in CFM units. But they aren't the same. When you see CFM (cubic feet per minute) in a product's specifications, it refers to the airflow of the fan itself, without any filter inserted. You can think of CFM as the fan's "air delivery rate."  CADR is the air purifier's "clean air delivery rate." as it measures airflow with a filter in place. So, CFM will always be higher than CADR, because a filter, even a new one, reduces airflow. If a manufacturer shows CFM and CADR as equal or lists the CADR as higher than the fan CFM, you should question this.

Look carefully! Make sure the CADR given is in cubic feet (CFM), and not in cubic meters (unless the room size you are using is also in square meters.) Sometimes models sold outside the US will use cubic meters, resulting in a higher apparent CADR.

Why does CADR matter?

If the CADR is too low for the square footage of the space, the air purifier it will not be powerful enough keep up with new air pollution entering the room. If the CADR is too high, it's essentially overkill, often at a higher price and using more energy.

Perhaps the easiest way to determine if the right CADR for the size of your room is the Two-Thirds Rule. This rule, from AHAM, says that the CADR should be 2/3 the room size.

Room Size X .66 = CADR  

If the room size is 350 square feet, the minimum CADR to clean the room effectively would be 231.

Or you can multiply the CADR by 1.55 and this will give you the maximum room size. The AHAM rule assumes an eight-foot ceiling height.

CADR X 1.55 = Room Size  

If the CADR is 200, the maximum room size it would clean effectively is 310 square feet. This rule assumes slightly under five air changes per hour (ACH). Depending on your situation, a lower ACH may be fine (two, three, or four ACH).

There's catch with CADR.

CADR only measures the air cleaning capability for new, unused particle collection media (filter or cartridge), over a 20-minute period. It is valuable because it provides a standardized comparison between brand new air purifiers. Unfortunately, it only measures new-product performance and doesn't tell you anything about effectiveness or cost-to-own over time. 

CADR is like a snapshot of a brand-new filter. In order to measure effectiveness, we need to see the movie, or the performance over time.

That's where yet another term—CCM—comes in. CCM or Cumulate Clean Mass testing is a method commonly used in countries with extreme pollution and it provides a picture of the clean air delivery rate over a longer period of time. CCM measures the amount, in volume of particulate matter, that the air purifier captures before the CADR drops to 50% of the purifier's original CADR. The higher the particle CCM, the longer period a filter can go before replacement.

CCM is a better measure of effectiveness over time than CADR. Unfortunately, few air purifier brands sold in the US conduct CCM testing – perhaps because the results wouldn’t look good, due to rapid filter clogging that can occur with HEPA filters.

At Agentis Air, we conducted CCM performance tests for dust loading, to compare Brio’s effectiveness with comparable HEPA air purifiers. Brio’s APART technology doesn’t use a blocking and clogging technology. Instead, it draws particles away from the air flow and captures them in a collection cartridge, so CADR stays high over the collection cartridge life. See the results here.

What About Air Changes Per Hour?

ACH is as important as CADR, and they work together. For air purifiers, Air Changes per Hour is the number of times the air in a room circulates through the purifier over a one-hour period. The more air changes per hour, the faster an air purifier will clean the room and more effective it will be at keeping it clean. Assuming it is also filtering efficiently.

A higher ACH increases the number times the air recirculates in an hour, but also decrease the size of the room that can be cleaned. An ACH of 2 means the air in the room goes through the air purifier every 30 minutes. An ACH of 4, every 15 minutes.

The best ACH for you depends on your air quality. If your air quality is relatively good, an ACH of 2 may be fine. For more polluted indoor air, or with acute health issues, a higher ACH is better.

PM, AQI and IAQ are all important to understanding your air quality issues. CADR, ACH, and CCM are all important in measuring air purifier performance.

Wait, there's more! HEPA, PCO, and APART™ are acronyms for different air purification technologies or methods: High Efficiency Particulate Air filter, Photocatalytic Oxidation, and Advanced Particle Removal Technology, respectively.

Learn how HEPA, PCO and APART differ and how choose the right air purifier.