What is a HEPA Filter and When Do I need a HEPA Filter?

HEPA is abbreviation of “High Efficiency Particulate Air” filter (As officially defined by US Department of Energy). HEPA filter is capable of removing theoretically at-least 99.97% of dust, pollen, bacteria dander, allergens from the fur of dogs or cats and any-other airborne particle of size 0.3 microns (µm). This particle diameter corresponds to most penetrating particle size (MPPS), being worst case scenario. Particles larger or smaller than MPPS are captured at even higher efficiency. 99.97% efficiency is the worst efficiency for the worst case particle size. Efficiency rating is better than 99.97% for all other particle sizes.

The HEPA filter is a pleated mechanical filter made of glass fiber or filter paper. It has large filter surface, established high quality and performance even in difficult environments.

History and Applications of HEPA Filter

HEPA filters were first developed in 1940s and were employed to prevent spread of radioactive contaminants. Then, these filters were introduced on commercial level in next decade to eliminate bacteria, pollen, viruses, dander and dust. With the passage of time, technological advancements demanded need of HEPA filters for cleaner air. Hospitals, pharmaceutical manufacturing, electronics, aerospace and nuclear power were few sectors that needed highly efficient filters.

Other application areas of HEPA include HVAC industry, Industrial and domestic vacuum cleaners and airlines. Recent pandemic of Covid-19 has changed our lives a lot. HEPA filters have been found effective in capturing SARS CoV-2.

Types of HEPA Filter

To be very precise, HEPA filter do not have types. Filter can be either HEPA or not HEPA. They may be classified on the basis of their efficiency and maybe categorized and compared on the basis of efficiency. When looking for HEPA filter, you will definitely come across the terms like HEPA type, HEPA like, HEPA style, 99% of HEPA. These terms are pointless and create confusion among consumers. And, if the user is not well aware of filters; he might end up buying lower quality filters. 

Above mentioned terms for HEPA filters are used for those filters, that don’t meet the HEPA standards. Certainly they are unable to remove 99.97% of 0.3 micron (µm).

True HEPA filters are standard filters meeting desired specifications. Term “true” refers to standard HEPA filters and to differentiate from other HEPA like filters (not HEPA). True HEPA doesn’t have any added or special qualities as compared with standard HEPA filters. Standard/True HEPA filters are widely used in air purifier, vacuum cleaners, furnace filters etc.

Classification of HEPA Filters

HEPA filters are classified on the basis of levels of efficiency. This classification is used to categorize HEPA filters among each other. Higher grade depicts the superiority of filter over other.

  • HEPA H10: pass more than 15% of 0.1 micron particles per liter of air.
  • HEPA H11: pass a maximum of 5% of 0.1 micron particles per liter of air.
  • HEPA H12: pass more than 0.5% of 0.1 micron particles per liter of air.
  • HEPA H13: pass up 0.05% of 0.1 micron particles per liter of air.
  • HEPA H14: pass up 0.005% of 0.1 micron particles per liter of air.

Above classification shows that HEPA H14 and H13 are high end filters and are referred as medical grade HEPA filters. Medical grade HEPA filters are generally used in pharmaceutical manufacturing and electronic control rooms as they have a greater particulate retention rate. High end vacuum cleaners also use this high end H13 HEPA filters. For cleanest air, HEPA H13 or H14 is recommended. 

Minimum Efficiency Reporting Values (MERVs)

Minimum efficiency reporting values indicate filters ability to capture larger particles in the range of 0.3 and 10 microns (µm). These ratings have been derived from test method developed by American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE). MERVs help in concluding following results.

  • Helpful in comparing the performance of different filters.
  • Higher MERV rating indicates that the filter is better at trapping specific type of particles.

MERV Rating

Average Particle Size Efficiency in Microns

1 - 4

3.0 - 10.0 less than 20%

6

3.0 - 10.0 49.9%

8

3.0 - 10.0 84.9%

10

1.0 - 3.0 50% - 64.9%, 3.0 - 10.0 85% or greater

12

1.0 - 3.0 80% - 89.9%, 3.0 - 10.0 90% or greater

14

0.3 - 1.0 75% - 84%, 1.0 - 3.0 90% or greater

16

0.3 - 1.0 75% or greater

18

0.3 – 10 micron greater than 99.99%

How do HEPA Filters work?

Working principle of HEPA filters can be divided into three stages namely inertial impaction, direct interception, diffusion and sieving. Let’s look at brief description of each stage.

Inertial Impaction

In first stage of filtration, inertia acts on large particles suspended in flow stream. These particles are heavier than the fluid surrounding them. When fluid changes direction to enter the space, particles continue their motion in straight line, due to inertia. These straight moving heavy particles collide with media fibers, whereby they’re trapped and held. HEPA filters pollutants like pollen by this mechanism of inertial impact.

Interception

Interception works on mid size particles that are not big enough to be captured by inertial impact and not small enough to diffuse with flow stream. These semi range size particles follow the fluid stream and are captured once they touch a fiber.

Diffusion

It works on small sized particles. Being small, these particles are not held in place by the viscous fluid and diffuse within the flow stream. This type of movement is referred to as Brownian movement.  When smaller particles transverses the flow stream, they collide with the fiber and hence captured.

Sieving

It is most common mechanism in filtration. Sieving occurs when the particle is too large to fit between the fiber spaces. In many cases, the particles that accumulate on the surface of the filter contain a large percentage of clothing lint and fibers. Since they do not penetrate into the body of the filter media, they do not significantly contribute to pressure drop in the filter. Instead, large percentage of fibers trapped by sieving acts as additional filter media increasing the efficiency of the filter.

Below is the graph showing efficiency of HEPA filters versus particle size. It also shows working principle for each range of particle size.

It is evident from graph that larger the particle, better a HEPA filters out the particle.  Further, note the dip in graph and observe corresponding particle size. It shows that HEPA has lowest efficiency of 99.975% for 0.3 micron particle size. It is the most penetrating size of particle. HEPA performs better for smaller or larger particle size than this 0.3 micron.

HEPA Filter
Particle Efficiency vs Particle Size of HEPA FILTER

HEPA Filters and Vacuum Cleaners

Domestic vacuum cleaners with HEPA filters are available in market. Quality of air in home is greatly affected by type of vacuum cleaner you own. Vacuum cleaners at home are used to collect dust, allergens, pet dander and hair. If any person at your home suffers from allergy, asthma or other respiratory issues raised by particle allergens, then you must look for HEPA filter vacuum cleaner. Studies have revealed that traditional vacuum cleaners can aggravate allergies by redistributing allergens on floor back in air you are breathing. Hence, vacuum cleaners with HEPA filter can alleviate allergens from spreading in air.

Frequently Asked Questions (FAQs)

What is difference between HEPA filter and regular filter?

The HEPA filter is a pleated mechanical filter made of glass fiber and activated carbon based materials. It has large filter surface, established high quality and performance even in difficult environments. While, regular filters are made of porous materials like cotton paper sheets and polyester.

HEPA filter offers few added benefits like less airborne particles and dust, fewer problems of allergies and asthma.

 

Are all HEPA filters same?

HEPA filters are either HEPA or not HEPA. There are no types of HEPA filters. HEPA like, HEPA type these terms are only market tactics to confuse the customer. So, all HEPA filters meeting established criteria are same. HEPA filters are only classified on the basis of efficiency and for comparison purposes. Below are the different grades of HEPA filters.

    • HEPA H10: pass more than 15% of 0.1 micron particles per liter of air.
    • HEPA H11: pass a maximum of 5% of 0.1 micron particles per liter of air.
    • HEPA H12: pass more than 0.5% of 0.1 micron particles per liter of air.
    • HEPA H13: pass up 0.05% of 0.1 micron particles per liter of air.
    • HEPA H14: pass up 0.005% of 0.1 micron particles per liter of air.

 

 

How often should I change HEPA filter?

Some vacuum cleaners use high particulate HEPA filters for improved indoor air quality. Although HEPA filters last long, but with the passage of time HEPA filter needs to be replaced for improved performance of vacuum. To be precise, it is difficult to define exactly how long a HEPA filter should be used. In a domestic use, HEPA filter needs replacement between 2 to 3 years.

Other equipment like air purifiers either come with light indication showing that filter needs to be replaced. While others come with user manual indicating, exact duration of HEPA filter usage.

 

What is so special about the size, 0.3 microns?

The size of 0.3 microns is referred to as MPPS (most penetrating particle size). Studies have proved 0.3 micron sized particle to be most penetrating particle and it passes through the filter more easily as compared to other larger or smaller size particles. Therefore, HEPA filters are rated on capturing efficiency of 0.3 micron MPPS particles. HEPA offers 99.97% efficiency for these MPPS particles. Above and below this size, HEPA performs even better than 99.97%.

 

 

How did HEPA filtration originate?

HEPA filters were first developed in 1940s and were employed to prevent spread of radioactive contaminants. Then, these filters were introduced on commercial level in next decade to eliminate bacteria, pollen, viruses, dander and dust. With the passage of time, technological advancements demanded need of HEPA filters for cleaner air. Hospitals, pharmaceutical manufacturing, electronics, aerospace and nuclear power were few sectors that needed highly efficient filters.

 

When is a HEPA Filter Important?

HEPA filter is one of products available for providing cleaner air at home, hospital and in industrial setups. It is found in variety of air-cleaning products. HEPA filters usage becomes vital, when you want to avoid dust induced allergies and asthma issues. Airborne particles that aggravate allergy problems are effectively captured by HEPA filters. Using HEPA filters in air purifiers, HVAC systems and vacuum cleaners can help avoiding allergy problems. In these scenarios, HEPA filters play crucial role.

 

What is use of HEPA filters in vacuum cleaners?

Vacuum cleaners with HEPA filters are available in market. Quality of air in home is greatly affected by type of vacuum cleaner you own. Vacuum cleaners at home are used to collect dust, allergens, pet dander and hair. If any person at your home suffers from allergy, asthma or other respiratory issues raised by particle allergens, then you must look for HEPA filter vacuum cleaner. Studies have revealed that traditional vacuum cleaners can aggravate allergies by redistributing allergens on floor back in air you are breathing. Hence, vacuum cleaners with HEPA filter can alleviate allergens from spreading in air, ultimately protecting residents from allergies and asthma.

How to buy a HEPA vacuum cleaner?

Vacuum cleaners with HEPA filters are recommended if, you have allergy and asthma patients at home. Many renowned brands offer vacuums with HEPA incorporated. When purchasing a vacuum cleaner, thoroughly read specifications and only purchase a vacuum if it clearly mentions HEPA filter, apart from other features. You may read our following articles to explore buying options.

 

Are HEPA filters expensive?

HEPA filters are relatively expensive than other contemporary filters. And it is fairly reasonable to spend money on HEPA filters, being quite efficient in capturing dust and other airborne particles. Studies have proved that HEPA filters are good for better air quality. But, it is pertinent to mention here that mostly we get fooled by marking tactics and end up buying expensive filters to keep our good health. Manufacturers market and sell filters with a high price tag to make their filters superior. So, if the user is unaware companies charge you higher for HEPA filters. HEPA filters are not that much high tech and not necessarily have to be expensive.

Do HEPA filter catch viruses?

Air quality has remained a concern for home owners and business owners. HEPA filters are capable of capturing 0.3 micron particles with efficiency of 99.97%. This particle size is associated with most pathogens. So, HEPA filter is effective in catching viruses. It can be more effective, if it is used with combination carbon filters or UV lights. It can enhance effectiveness of HEPA filter in catching viruses.

 

Can we clean and re-use HEPA filter?

There are two ways of cleaning HEPA filters. You may either vacuum clean the filter or wash the filter. Experiments have revealed that vacuuming the filter may enhance the performance, but effect will be small. While, washing the HEPA filter decreases performance. It is recommended to replace a HEPA filter for optimum performance after recommended duty cycle.

What is a medical grade HEPA filter?

HEPA H13 is a medical grade filter being among highest tier of HEPA grades. Medical grade HEPA filters are commonly used in pharmaceutical manufacturing and electronic control rooms because they have a greater particulate retention rate. This means medical grade HEPA filters are more efficient in removing harmful toxins from the environment.

What is efficiency of HEPA filter against Covid-19?

Virus causing Covid-19 is 0.125 micron approximately. The graph of HEPA filter efficiency against particle size depicts that HEPA filters captures 100% of particles of this size (0.125 micron). This implies air purifiers and vacuum cleaner with HEPA filter would efficiently catch viruses and other aerosol droplets of saliva containing Covid-19 virus. Hence, HEPA filter can prove quite efficient in avoiding spread of Covid-19.

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