If you have been looking for an air purifier, you might have already encountered a couple of jargon and terms.
Although most of those terms are somewhat easy to understand, there are some that can leave you scratching your head.
For example, what is a HEPA filter?
HEPA stands for High-Efficiency Particulate Air (filter). This air filter has high efficiency in removing dust, mold, pollen, bacteria, and other airborne particles with a size of 0.3 microns.
However, that is just a definition that the U.S Dept of. Energy provided. There is so much to HEPA that you should know about.
And you can learn about it through our ‘HEPA filter 101’ guide! So, without any delay, let’s dive in.
Understanding HEPA Efficiency Rating
As you know by now, HEPA filters have a 99.97 percent efficiency in capturing airborne particles that are 0.3 microns in size.
This diameter specification might seem a little confusing at first. But all you have to know is that the specification responds to the worst case.
The thing is, 0.3-micron particles are labeled as MPPS, which stands for the Most Penetrating Particle Size.
That means the efficiency number you see on a HEPA filter states the worst possible efficiency rating.
HEPA Filters and MERV Rating
MERV, or Minimum Efficiency Reporting Values, reports the ability of a filter to capture particles between 0.3 microns and 10 microns in size.
Why does this value matter? Well, it comes in handy for the following reasons –
- The value will let you easily compare the performance of different types of filters
- ASHRAE develops a test method for the rating, and the test is consistent
- The higher the MERV rating, the better the filter’s ability to capture a particular type of airborne particles
However, if you do not know what the MERV rating is stating, you will not be capable of using the information it is responding to.
| MERV Rating | Particle Size Efficiency in Average |
| 16 or higher | 0.3 to 1.0 microns with 75 percent or higher efficiency |
| 14 | 0.3 to 1.0 microns with 75 percent to 84 percent efficiency and 1.0 to 3.0 microns with 90 percent or higher efficiency |
| 12 | 1.0 to 3.0 microns with 80 percent to 89.9 percent efficiency and 3.0 to 10.0 microns with 90 percent or higher efficiency |
| 10 | 1.0 to 3.0 microns with 50 percent to 64.9 percent efficiency and 3.0 to 10.0 with 85 percent or higher efficiency |
| 8 | 3.0 to 10.0 microns with 84.9 percent efficiency |
| 6 | 3.0 to 10.0 microns with 49.9 percent efficiency |
| 1 to 4 | 3.0 to 10.0 with less than 20 percent efficiency |
How Do HEPA Filters Work?
When people first hear about HEPA filters, they think of them like a net. And it makes sense.
When it comes to a net, anything larger than the holes will get captured by the net.
The mechanism is somewhat the same for the HEPA filters. However, there is so much more to HEPA filters.
Capturing the Large Particles
When any particles of the air purifiers are referred to as big, the particles are typically larger than 10 microns.
In comparison, the hair on your head is about 50 microns in size. And if you take that into consideration, 10 microns is significantly small!
Nonetheless, when these big particles get into the HEPA filter, they will get stuck between the fibers.
Filtering the Smaller Particles
Air purifiers refer to particles smaller than 10 microns by “Small Particles.” If we put that into perspective, these particles are between 0.3 to 1 micron in size.
Basically, these have the size of bacteria. These particles can fit between the gaps of the filter.
However, that is not a problem for HEPA filters. The particles will try to go with the airflow around the HEPA filter.
And they are a bit heavy. Due to their heft, they get stuck to the fiber.
Trapping the Extremely Small Particles
So, what about the particles that are smaller than 0.3 microns in size?
Well, the science behind the HEPA filters gets a little interesting at this point.
These particles have little to no mass to them. For that reason, they bounce around the filter like a pinball. They usually maintain a zigzag pattern.
But the bouncing does not happen forever. The small particles eventually hit a gas molecule. And when that happens, they end up hitting the fibers.
Scientists call this process diffusion.
HEPA Filter Types + Mechanisms of HEPA Filter Filtration
Many filters fall under the HEPA standard. Each of them is basically a different variation of the HEPA filtration unit.
And they have a different working mechanism. Let us go through them to make you better understand the filtration process.
1. HEPA-Like
A lot of the filters fall into this category. Manufacturers term these filters as “HEPA-like,” “HEPA-type,” “HEPA-style,” and “99 Percent HEPA.”
Even though these terms might sound a little different, they are all similar.
Now, all of these terms tell you one thing. That is, the filters do not strictly adhere to the HEPA standard.
But what makes these filters different is that they are not independently tested.
Nonetheless, when it comes to the mechanism, these filters are very close to actual HEPA.
But when it comes to performance, they work as well as the True HEPA filters. However, the efficiency does not remain the same for all scenarios.
2. True HEPA
The standard HEPA filers are called True HEPA. Although the “True” prefix might sound more like a marketing term, it actually states that the filter is not a HEPA-like filter. Instead, it is a filter that strictly adheres to the HEPA standard.
That said, the working mechanism of a True HEPA filter strictly adheres to the standards of HEPA. That means these are the real deals regarding the efficiency HEPA proudly boasts.
By definition, all the True HEPA filters have 99.97 percent efficiency in capturing airborne particles that are 0.3 microns in size.
3. Medical Grade HEPA
Medical HEPA, also known as H13 HEPA filters, are a special type of filter.
These are mostly for hospital settings. But what is the difference between True HEPA and Medica Grade HEPA?
Well, there is a difference in terms of mechanism and the targeted pollutants.
For True HEPA, the mechanism is for capturing contaminants that are 0.3 microns in size.
On the other hand, the H13 HEAP filters aim to trap smaller particles. That is, the particles that are 0.1 microns in size.
What about efficiency? Medical Grade HEPA does not disappoint in that criterion either. These can capture the 0.1-micron particles with a 99.95 percent efficiency.
Now, does the Medical Grade HEPA filters only present in Medical Air Purifiers?
Not really! You will find them in most of the common HVAC appliances. And you can definitely get one for residential use.
Frequently Asked Questions
1. What are the benefits of a HEPA filter?
The biggest advantage of having a HEAP filter air purifier is that the device can effectively capture air particles. These can capture extremely small and harmful particles. That includes pet dander, pollen, dust mites, and smoke. So, with a HEPA air purifier, the air you will breathe will be extremely clean.
2. How long do HEPA filters last?
The lifespan of the HEPA filters will depend on the load you put on them. For example, if you are using the air filter regularly, these filters can last anywhere from 24 months to 36 months. However, replacing the HEPA filters once every year is a good practice.
3. Can you wash HEPA filters?
You can wash the washable, otherwise known as permanent HEPA, filters. And to wash them, you just need to hold them under cold water. No matter what, do not touch the filter material. If you do, you will disrupt the working mechanism of the filter, and it will not work efficiently.
Read More: What Is A Pre-Filter In An Air Purifier?
Final Words
Are you still looking for the answer to the question of what is a HEPA filter?
Well, in a nutshell, HEPA is a particular type of air filter. At its true form, this filter can capture air particles that are 0.3 microns in size with 99.97 percent efficiency.
Last Updated on January 14, 2023
