What Is a HEPA Filter?

HEPA stands for high-efficiency particulate air. A HEPA filter is a type of pleated mechanical air filter that satisfies the HEPA standard. Many air purifier manufacturers claim that HEPA filters can significantly improve your indoor air quality.

In this article, we will get into more detail on what a HEPA filter is, how it works, and how effective it is. We’ll also provide you with a better understanding of what the HEPA standard is and how to know if an air purifier really meets it.

What Is a HEPA Filter?

As stated in the beginning, the HEPA acronym represents high-efficiency particulate air, also known as high-efficiency particulate arrestance or high-efficiency particulate absorbing. HEPA filter eliminates more than 99.97% of airborne particles sized 0.3 microns or above. For particles of other sizes, the efficiency will be even higher. HEPA filters trap mold, pollen, dust, and other airborne particles. It’s even able to catch bacteria, viruses and some microorganisms smaller than 0.3 microns.

Unlike other filters, most HEPA filters are built using thin fibers of glass and activated carbon-based materials. This combination creates a fine mesh whose role is to catch the above-mentioned particles alongside potentially dangerous allergens and compounds such as dirt, cigarette smoke, pet dander in some models, and others.

We should also note that HEPA filtration functions based on mechanical principles, while other air treatment technologies such as ionic or ozone ones use negative ions and ozone gas. That means that chances of inducing respiratory side-effects like asthma significantly decrease when using a HEPA air purifier.

The HEPA filter uses three different methods to remove these harmful particles from the air:

  • Some particles get caught after crashing into filter fibers
  • Others get filtered by interception due to flying too close to a fiber
  • The third way is diffusion – a process of particles crashing into each other and then getting absorbed by the fibers of the HEPA filter. This usually happens at lower airstream speeds

What Is the HEPA Standard?

HEPA filters were initially created in the 1940s to be used in containers that store nuclear materials. The main role of HEPA filters back then was to prevent nuclear radiation from getting in touch with particles of moisture and dust, which would allow radioactive pollutants to further spread through air ducts and corridors. That explains why the HEPA air filtration standard was set by the U.S. Department of Energy.

Later on, HEPA filters have become necessary in various industries. Vacuum cleaners, HVAC units, and stand-alone air purifiers all started using the HEPA filter in the 1960s, so it’s ever since then that the HEPA filters are available on the market for public use. All HEPA filters must satisfy the HEPA standard which states that the filter must eliminate at least 99.95% (European Standard) or 99.97% (ASME, U.S. DOE) of particles that are 0.3 microns in size. The efficiency increases with particles both smaller and larger in size. That implies that only 3 out of 10.000 particles would get trapped in the filter. Keep reading to learn more about HEPA’s filtration efficiency.

How Effective Are HEPA Filters Vs Other Such Filters?

Before getting into more detail on filtration efficiency we should introduce a value called Minimum Efficiency Reporting Values (MERV), which measures what percentage of larger particles, sized 0.3-10 microns, the filter removes. Here’s a table of filter types based on MERV ratings, derived from ASRAE’s (American Society of Heating, Refrigerating, and Air Conditioning Engineers) test method:

MERV Rating Average Particle Size Filtering Efficiency
16 0.3-10.0 microns 75% or more
14 0.3 – 1.0 omicrons
1.0 – 3.0 omicrons
75% – 84%

90% or more

12 1.0 – 3.0 omicrons

3.0 – 10.0 omicrons

80% – 89.9%

90% or greater

10 1.0 – 3.0 omicrons

3.0 – 10.0 omicrons

50% – 64.9%

85% or greater

8 3.0 – 10.0 omicrons 84.9%
6 3.0 – 10.0 omicrons 49.9%
1-4 3.0 – 10.0 omicrons up to 20%

The higher MERV rating, the more efficient the filter is in trapping particles. Keep in mind that the HEPA filter is normally considered equal to a MERV 17.

Respectable air purifier manufacturers will clearly state the MERV rating on their air filters and air purifiers. In some cases they even point out which particle size and which sort of pollutant is their unit meant for.

The Difference Between HEPA And Similar Filters

In case you consider purchasing a HEPA filter, you should keep in mind that there are several variations of HEPA available. Remember that the one approved by the U.S. HEPA standard is the right one.

You’ll often come across air filters that are being selled as “HEPA-style” or “HEPA-like”. Obviously, those terms stand for nothing, since they don’t really say whether the filters satisfy the HEPA standard. That’s why some companies whose filters do meet the standard decided to market them as “True HEPA”.

Besides the required filtration efficiency, we should take a look at another aspect of the HEPA standard. Let’s underline how important it is for the construction of the filter case to be airtight. Cheap air purifiers, such as “HEPA-style” ones usually can’t produce an effective, air-tight filter, and having the airflow able to get past the filter implies that the filter is failing to do its job. That’s another reason to avoid “HEPA-like” and “HEPA-style” variations and always go for the real HEPA filter that meets the U.S. HEPA standard.

What HEPA Can’t Do?

HEPA filters do help eliminate certain particles from the air, but there are also some pollutants that won’t be affected by HEPA. Those include:

  • Volatile Organic Compounds (VOCs): Those are the airborne chemicals commonly derived through off-gassing of construction materials, cleaning products apart from cosmetics, and other products in your home. Some VOCs are carcinogens, and exposure to them can pose a significant risk for health. Unfortunately, HEPA filters can’t eliminate VOCs due their rather small size.
  • Mold: When it comes to mold spores, HEPA is able to trap them, since they’re large enough. The problem here is that they keep living on the filter surface. Mold spores can then feed on the other particles trapped in the filter and later on release new spores.
  • Bacteria: Similar to mold spores, bacteria can also be caught on the filter. As they die there, bacteria start emitting endotoxins, which can induce inflammatory and atopic symptoms.

How to Overcome the Cons of HEPA Filter

Although the HEPA filter is a great addition to the improvement of the air quality at your home, it certainly doesn’t resolve all of the issues related to pollution. Below you will find some steps you should take in order to resolve those other pollutants.

  • Vacuum clean and wipe the dust in your home often. This will help reduce harmful particle concentrations in the room and eliminate contaminants caught on furniture, rugs, and other fabrics.
  • Keep your pets only in certain spaces of your home.
  • In case the outdoor air quality in your area is good, ventilate as much as possible, since this can always make room for better air quality. Keep in mind that letting the fresh air flow around the space is especially important after you do any cleaning.
  • People with allergies should use special pillows and mattresses since this can help remove a vast number of harmful particles.

It’s important to note that every air purifier needs to be cleaned, and its filter replaced at regular intervals, as specified by the manufacturer, in order to be effective. Mold and other living pathogens tend to stay alive on the filter and further reproduce. This is especially the case with higher humidity or temperatures. In such conditions, bacteria and mold can even live and reproduce in the filter that was meant to eliminate them. That’s why filter maintenance is so crucial. Each product comes with a user manual, so cleaning your device and replacing its filter shouldn’t be difficult.

Should I Purchase a HEPA Filter?

When answering this question it’s crucial to understand that HEPA filters can’t provide the solution for all issues related to air quality.  We’ve already talked about the particles, such as VOCs and viruses, that HEPA can’t trap, due to their small size. For those of you concerned about such problems HEPA won’t be able to help.

On the other hand, if the air at your home is polluted with animal dander, PM2.5 from smoke, dust, or pollen, a HEPA filter might be just what you need to improve your indoor air quality.

Final Words

We’ve come to the end of our post on what a HEPA filter is. We hope you like the article and find it helpful. Remember that HEPA filters can eliminate particles between 0.3 and 10 microns in size. We must note once again that there are many imitations of HEPA available out there, so make sure that you’re buying a true HEPA filter. As always, feel free to post a comment in case you have any questions or need more detail on a particular point. Good luck with improving your indoor air quality!