Buying a HEPA-certified air purifier

Throughout your research for an air purifier, you may have come across the acronym ‘HEPA’ in regards to filters. HEPA air purifiers are widely known for their ability to remove ultrafine and nano particulate matter from the air and improve air quality in indoor spaces and rooms. However, you may be wondering: what, exactly, differentiates HEPA-certified filters from standard filters? Are they necessary to achieve clean air? Read on to learn more about HEPA and its capacities to fight air pollutants in your rooms at home and at work.

HEPA defined

HEPA, or ‘high-efficiency particulate air’ filter, also known as a ‘true HEPA’ filter, is a pleated filter that removes 99.95% of airborne particles and allergens measuring a size of 0.3 microns (µm) from the air as defined by the Environmental Protection Agency (EPA)¹. A filter only receives HEPA certification if it can remove these pollutants from a room in a single pass. HEPA is a European certification overseen by European standards EN 1822 and EN ISO 29463.

The 0.3 µm barrier

Why was the particle size of 0.3 µm chosen? Of all particle sizes, 0.3 µm is the particle size that is the most difficult to filter (otherwise known as ‘MPPS’ or the most penetrating particle size)¹. Therefore, it is the worst case scenario. An air purifier containing a true HEPA filter can filter particles and allergens both larger and smaller than 0.3 µm from a room with an even higher efficiency, dramatically improving air quality and achieving clean air. HEPA filters are able to capture ultrafine particles down to a size of 0.01 µm.

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HEPA filter limitations

The limitation of HEPA filters is their inability to trap and filter volatile organic compounds (VOCs) and ozone from indoor spaces and rooms. This is why it is so important to have complementary filtration technologies (like activated carbon filtration) in an air purifier or air cleaner to thoroughly improve your indoor air quality. Eoleaf’s devices come with 8 different filtration technologies!

How are HEPA filters created and how do they work?

To create a HEPA filter, synthetic fibres and glass are tightly woven together. The synthetic fibres serve as the filter’s membrane whereas the glass fibres trap the particles².

A HEPA filter has four ways of functioning:

1. Sieving: particles that are too large to pass through the filter’s fibres get stuck in the filter’s membrane.
2. Direct impact: particles that are too large tend to travel in a straight and direct path, leading them to get stuck.
3. Interception: inertia leads particles to travel more randomly and veer off course, causing them to get stuck.
4. Diffusion: extra small particles bounce around erratically which leads to a collision with the filter’s fibre media³.
• The diffusion process is particularly effective for removing particles under 0.2 µm including the coronavirus⁴

HEPA filtration grades

HEPA filters must be tested by both the manufacturer and an independent testing facility to ensure conformity to the HEPA standard. The efficacy and integrity of HEPA filters on air quality is tested using a DOP (Dispersed Oil Particulate) test. How this test works is oil in the form of an aerosol is distributed into the upstream flow of the filter media. A calibrated photometer is then used to measure the number of particles in downstream flow⁵.

HEPA filters are separated into five classes as follows:

• H10
• Filtration rate: removes 85% of pollutants from a room
• Allows 15,000 particles of 0.1 micron per litre of air to pass through
• H11
• Filtration rate: removes 99% of pollutants from a room
• Allows 10,000 particles of 0.1 micron per litre of air to pass through
• H12
• Filtration rate: removes 99.5% of pollutants from a room
• Allows 500 particles of 0.1 micron per litre of air to pass through
• H13 (as used in Eoleaf products)
• Filtration rate: removes 99.95% of pollutants from a room
• Allows 50 particles of 0.1 micron per litre of air to pass through
• H14
• Filtration rate: removes 99.995% of pollutants from a room
• Allows 5 particles of 0.1 micron per litre of air to pass through

H13 and H14 HEPA filters

Filters of the H13 and H14 categories are considered to be ‘medical-grade’ or ‘hospital-grade’ HEPA filters. These are the grades typically used in hospitals, patient rooms, operating theatres, and in pharmaceutical settings but have found other applications in places where clean air is essential. Eoleaf’s products, for example, use HEPA H13 filters. Although H14 filters have a slightly higher filtration rate, thus decreasing the speed and efficiency of the purification process.

Minimum Efficiency Reporting Values (MERVs)

When comparing the performance of different filters, it is important to consider their MERV rating. These values are used to report a filter’s ability to capture larger particles between 0.3 and 10 µm. Filters with a higher MERV value are more efficient at trapping particles of a specific type in your room. The following chart, provided by the EPA, compares MERV values:

Source ¹

The benefits of a HEPA air purifier

For those looking to achieve clean air and improve air quality, a HEPA air purifier is your best bet.

A true HEPA filter can remove the following pollutants from a room:

• Allergens (pollen, dust and dust mites, and pet hair and dander)
• Most dust particles measure less than 5 microns in size, dust mites measure about 20 microns, and dust mite droppings measure about 10 microns; all dust-related air pollutants are invisible to the naked eye
• Pet dander measures roughly 2.5 microns
• In-tact pollen grains usually measure around 10 microns but pollen grains often fracture and become small enough to fall into the PM2.5 size category: studies show that the pollen season is worsening due to climate change and air pollution
• A 2011 study found that air purifiers containing HEPA filters can provide significant benefits to those suffering from allergies of all types (especially due to allergens like pollen and dust) and can improve sleep quality⁶
• Another study found that HEPA filters significantly reduce medication requirements for patients experiencing allergic rhinitis due to airborne allergens⁷
• Fine and ultrafine particles (particle matter or PM) including those found in cigarette smoke
• A 2022 study found HEPA filters can drastically improve PM2.5 indoor air pollution and air quality⁸
• Another study from 2021 found decreased levels of indoor PM of all sizes with the use of a HEPA filter⁹
• Germs (viruses and bacteria)
• A 2022 study found that air purifiers equipped with medical-grade HEPA filters can dramatically reduce the rate of the spread of infection between patient rooms¹⁰
• Mould and its spores
• Mould spores can measure down to 4 microns (according to a recent study¹¹)

The use of a HEPA air purifier has been linked to improvements in respiratory disease symptoms like asthma and chronic obstructive pulmonary disease (COPD), a lower risk of air pollution-related diseases (including lung cancer in non-smokers), increased sleep quality, and a decreased risk of mental health disorders like anxiety and depression.

As mentioned above, a HEPA filter cannot remove volatile organic compounds (VOCs) from a room.

HEPA air purifiers in the workplace

Air purifiers with HEPA filters can also bring benefits to office settings. According to a 2017 study, occupants of ‘green buildings’ equipped with HEPA air purifiers that bring clean air and improved air quality experienced:

• A 26% increase in cognitive function scores 
• A 30% reduction in symptoms related to ‘Sick Building Syndrome’ (SBS)
• A 6% increase in sleep quality
• Improvements in productivity, performance, and fatigue levels¹²

Installing HEPA-certified air purifiers in your rooms at home and in the workplace can provide a myriad of benefits to users of these spaces.

How to choose a HEPA air purifier?