Last Updated on
An air purifier is a necessity in our homes nowadays. Asthma, allergies and other dirty air issues are common. You don’t need any air purifier – you need a quality one. However, what makes for a quality air purifier? Well, if you go to buy an air purifier you should look at it’s CADR and ACH ratings. But, what is CADR rating? Let’s get right at it.
What is CADR rating?
Cadr rating is a uniform standard gauge to determine the efficiency of any air purifier. In full, CADR is clean air delivery rate.In the 80s, the Association of Home Appliance Manufacturers (AHAM) came up with CADR rating. CADR measures the performance of portable air purifier without considering the underlying technology.
CADR is expressed in the volume of clean air delivered by a purifier. So, when you go shopping you will see the CADR rating of the air purifiers inscribed. The higher the rating, the faster the air purifier cleans air. For instance, a purifier with a rating of 400CFM will work better than one with 300CFM in a room of 400 square feet.
Also, if the air purifier is noisy:it’s CADR will be low. Noise is a critical factor to consider in an air purifier unit. A noisy unit is irritating. If a purifier is verified by AHAM, it will have the AHAM verifide mark. This mark will have the CADR rating and the suggested room size the air purifier will work best in. The CADR is meant to help prospective air purifier buyers make better choices when buying. Make sure you go for one that is CADR rated (one with the AHAM verifide mark).
How CADR rate is determined
An air cleaner is awarded a CADR rate by performing the ANSI/AHAM AC-1 test. The AHAM test is an easy to understand process. A purifier is put is a room of 10008 cubic feet. The room has measured levels of impurities. Then, the purifier is activated to clean the air in the room for 20 minutes. After this, the level of contaminants are measured and the air cleaner is given its performance rating.
AHAM has three standard ratings. You will find these inscribed in their seal. These CADR ratings represent a unit’s efficiency in cleaning tobacco smoke(10 – 450CADR), dust (10 -400 CADR), and pollen grain (20 – 450CADR) impurities. The air cleaner CADR is a set of three numbers. For example: 180/160/200, these represent the CADR for tobacco smoke, dust and pollen grains respectively.
AHAM recommends a two thirds rule the CADR of tobacco. Meaning, the maximum room size the unit can serve efficiently is: The CADR of tobacco divide by ⅔ (two thirds).
So using the example above:
The CADR of tobacco is 180.
So, the maximum room size this purifier can serve efficiently is:
= 180 / ⅔ = 270 square feet
Is the CADR rating effective?
Yes CADR is an important aspect to consider. Why?
- CADR considers both filter efficiency and air flow. For instance,if a filter has a CADR rate of 300CFM and 100 percent efficiency then the CADR is 300. But, if its efficiency falls down to 75 percent, then the CADR will be 250. The CADR test help balance between air cleaning efficiency and rate. This makes misleading marketing efforts blunt.
- The AHAM test has been around for over 30 years. Because of this, the CADR rating has been adopted by the Environmental Protection Agency, the Independent Watchdog Organization consumer union, the Federal trade, and China.
However, I will advise you to consider other aspects before making your purchase. The CADR rating has its limits.
Limitations of the CADR rating
- CADR test considers only three impurities – pollen grains, tobacco smoke and dust. So, other pollutants like bacteria,viruses, organic pollutants and other small particle impurities are not tested. These smaller contaminants make up most of the dirt in the air, cause most allergies & irritation, and are most dangerous.
- CADR makes much emphasis on how fast an air purifier circulates air. This means, the bigger the fan the higher the CADR rating. You can find an air cleaner with poor efficiency and high air circulation level having a high CADR rate.
- The CADR rating is calculated within twenty minutes. It does not look like an issue. But, look, if an air purifier has high efficiency; it will take up to an hour to clean and circulate air. However, an air purifier that filters only the large contaminants and circulates air faster will get a higher rating than the efficient one. That is misleading.
- CADR does not consider the technology used to purify air. For instance, a purifier that uses an ionizer, cleans air by ionizing solid particle. But, it does not trap these particles. Instead, it releases the dirty to the floor, and walls. This way the dirt easily get back to the air. This is dangerous. Because ionized particles easily get into your bloodstream when you breath. Also, units that use an ionizer to clean air generate ozone. Ozone is a byproduct of the ionizing process. The American Lung Association warns against using machines that produce ions or ozone. Ozone and these ions cause coughing,shortness of breath and chest tightness.
- Some purifiers’ performance can decline over time. This test does not show that because it is done within 20 minutes.
All that said, the CADR should not be the only factor to consider when buying an air purifier.
Like the CADR rating, The ACH rating is equally as important. In fact, the two ratings are closely related. ACH in full is the Air Changes per Hour . As the term suggests,ACH rating gives the number of times an air cleaner changes air within one hour.
The more times a purifier freshens air the higher the ACH rating.For example, if a unit is rated 4x ACH and another at 2x ACH; then the former is twice as fast. ACH rating also allow us to determine the maximum room size a particular unit can serve efficiently. For instance here:
If you have a unit with a CADR of 400CFM and a 6x ACH rate in a room of height 8 feet (from the floor to the ceiling). We can calculate the maximum room size the unit can serve efficiently.
How? Let’s find out:
The time limit for any ACH value is 1hour. So, multiply the CFM by the 60 minutes – one hour- and divide your answer by the height of the room(8ft). Then, divide your answer by the arch value.
400CFM x 60 minutes = 24000
24000/8feet = 3000
3000/6ACH = 500 square feet
In this case, this air purifier can work best in rooms of 500square feet and below. Notice that in a smaller room the number of times you get Fresh air exchange increases. You can get that by twisting the math above.
Now you know about CADR
CADR rating and ACH rating are critical specs to look for in a good air purifier. However, you should consider other specs because CADR and ACH ratings can be misleading at times. You can end up buying a noisy air cleaner, or with a unit that produces ions and ozone – you know how bad this can get. There are other factors you should consider in an air purifier. Much of that we have covered. But, if you missed some of them, here is a list of specs to look for in a quality air purifier:
- Its CADR rating
- Its noise level at maximum speed
- The technology used in the air cleaning process – avoid units that produce ozone and ions
- Filter efficiency and size
I think you now have enough information about CADR, ACH ratings. So,did you learn anything new. Or, did I leave out some critical points. Go on and leave me a comment.