Pros and Cons of HEPA Filter Air Purifiers, Dissected

A HEPA (High-Efficiency Particulate Air) filter can be an important part of common air purifier systems promising to improve the air quality in your home or office. But there are a lot of misconceptions about the HEPA standard, whether or not an air purifier or filter truly meets the HEPA standard, and what a HEPA filter can and can’t do. Let’s take a look at what the HEPA standard means and how a HEPA filter can deal with various types of pollutants in your home.

Read more about a new air purifier technology that destroys pollutants, instead of simply trapping them like a HEPA filter.

What is a HEPA filter?

The HEPA standard is defined by the U.S. Department of Energy. It might seem strange that the Department of Energy created an air filtration standard, but HEPA was first developed in the 1940s for use in facilities containing nuclear materials. Shielding can be used to contain radiation, but if particles of dust and moisture become irradiated, they can spread radioactive contamination through air ducts and corridors. HEPA filters were developed to keep potentially radioactive particles contained. Since then, it’s been used in numerous industries and applications. By the 1960s, HEPA filters were moving into the consumer market as filters for HVAC units, vacuums cleaners, and stand-alone air purifiers.

What HEPA air filters are good for

To understand how HEPA works, think of it as mesh of tangled fibers. The sheet is usually folded into pleats to increase the surface area and filter life. Air flows through the fibers and large enough particles get trapped when they hit the fibers. So it’s a size game which very clearly helps understand what HEPA can filter and what not.

HEPA works well and is effective at removing large enough particulate matter like pet dander, pollen, and dust mites. Other particulates can be caught but continue to cause concern on the filter which we’ll explain in the next section.

Where HEPA air filters fail

HEPA filter drawbacks include small particles passing through and possibility of mold growth on filter surface.

HEPA filter drawbacks

While HEPA filters remove some particulates from the air, there are many harmful contaminants in the air that aren’t particulate matter.

VOCs: Volatile Organic Compounds (VOCs) are airborne chemicals that mostly derive from off-gassing of building materials or products in our homes as well as cleaning products aside from other sources like beauty products. The most concerning health effect associated with VOCs is that some are well-known carcinogens. HEPA filters are unable to remove VOC’s as they simply are far smaller in size than what can be trapped.

Viruses: Much like VOCs, viruses are also too small to be removed. Despite this fact, HEPA based products were marketed for a long time with the claim to protect from viruses. The US Federal Trade Commission (FTC) has now regulated that HEPA filter based products can no longer make that claim.

Bacteria: While bacteria are large enough to be trapped, bacteria are understood to release endotoxins into the air stream when dying on the air filter surface. Studies have demonstrated that endotoxins cause inflammatory and atopic responses in nonasthmatic and asthmatic participants.

Mold: Mold spores are large enough to be caught in HEPA filters but stay alive on the filter surface. Other particles that accumulate and fill the filter start acting as nutrients and allow mold spores to potentially grow on and through the filter membrane and eventually release new spores into the air.

It is important to say that frequent replacement of filters is critical since pathogens collected on the filter can include live organisms and eventually pathogens are re-released into the air.

Should I buy a HEPA air purifier for my home?

A HEPA filter needs to be understood only to be a part of the solution in improving your indoor air quality. As you can tell above, HEPA has many shortcomings, particularly for submicron particulates such as VOCs and viruses.

For those that are concerned about larger particles such as dust, pollen, and animal dander – HEPA might be right for you. If you are concerned about other sources of indoor air pollution such as VOCs, viruses, and bacteria, HEPA might not be right for you.

Compensating for the shortcomings of HEPA

As mentioned above, because HEPA isn’t a complete solution that can address all indoor pollutants, these are some steps you can take to improve your indoor air quality by removing the source of the air pollutants:

  • Limit pets to certain areas of the house.
  • Vacuum and dust frequently to cut down on volume of particles in the room, and to remove pollutants trapped in rugs, drapes, and furniture that a HEPA air purifier wouldn’t be able to reach.
  • Open as many windows as possible during and after any cleaning.
  • For those sensitive to allergens, special mattress and pillow covers can greatly cut down on the pollutants you’re exposed to.
  • If you don’t live near a major source of pollution, you can always improve the air quality in your home by frequently opening the windows and letting in fresh air. Houses tend to trap and concentrate pollutants, so the outside air is almost always cleaner.

Learn more about source control, ventilation, and indoor air pollution here.

True HEPA vs. HEPA-like vs. HEPA-style

If you do decide that HEPA is right for you, pay attention to a few important variations of HEPA. It’s important to note that the U.S. HEPA standard is the one to look for.

To add confusion to the mix, some air filters are marketed as “HEPA-like” or “HEPA-style.” This is meaningless because terms don’t indicate that the filters actually meet the HEPA standard. Some manufacturers whose filters do meet the standard have begun using the term “True HEPA.”

The HEPA specification (which stands for High Efficiency Particulate Air and also known as High Efficiency Particle Arrestance) is based on the size of the particles and how many of them pass through the filter. To meet the standard, a filter must stop 99.97 percent of all particles that are 0.3 micrometers in diameter. That means that if you sent ten thousand 0.3 micrometer particles through a HEPA filter, only three particles would get through.

There’s another aspect of the HEPA standard that is often overlooked: the construction of the filter case must be airtight. If air flow can get around the filter, then the filter is not going to work very well. This is where you’ll often find flaws in air purifiers marketed as “HEPA-style.” It requires more precise manufacturing to create an effective, air-tight filter, and cheap air purifiers aren’t always up to the task.

Effectiveness of HEPA and non-HEPA filters

How effective can HEPA actually be? The chart below, adapted from an EPA report lists the MERV rating of filtration material corresponding to the typical contaminant that they address, along with the typical filter type found in the MERV rating group (from HEPA to “HEPA-like” filters).

Even though the MERV value is strictly performance based, you can still derive some value from the chart below, as it gives you an indicator of the limits of certain types (e.g. higher efficiency pleated filters vs. true HEPA filters). Generally, HEPA is considered the equivalent of a MERV 17.

Minimum Efficiency Reporting Value (MERV) Particle Size Removal Efficiency Particle Size and Typical Contaminant Typical Filter Type
13 ~ 16 75% to 95% 0.3 ~ 1 µm (micron)
Cooking oil, most smoke, insecticide dust, face powder, paint pigments
High-efficiency filters
Densely packed fibers capturing particles in air down to 0.3 µm in size. MERV of 13 brings 75% efficiency, versus a MERV of 16 with 95%.
9 ~ 12 90% to 95% 1 ~ 3 µm
Humidifier dust, lead dust, nebulizer drops
Pleated filters (HEPA-like, HEPA-type)
Extended surface with cotton or polyester media, usually 1 to 6 inches thick
5 ~ 8 35% to70% 3 ~ 10 µm
Mold, spores, dust mite, hair spray, fabric protector
Throwaway Filters
Synthetic media panel filters
1 ~ 4 Under 20% > 10 µm
Pollen, dust mites, sanding dust, spray paint dust, textile and carpet fibers
Throwaway Filters
Fiberglass or synthetic media panel, usually 1 inch thick
Washable Filters
Aluminum mesh, foam rubber panel
Electrostatic Filters
Passive self-charging woven polycarbonate panel

Reputable air purifier companies that have filtration-based units should clearly state their MERV rating, or state plainly what the particle size and type of contaminant their product can actually address.

Closing it all out

HEPA is good at removing larger particulate matter like pet dander, pollen and dust mites. Unfortunately, mold, VOCs, viruses, bacteria, and small particulates under 0.3 micrometers can not be removed safely from the air with an HEPA-based air purifier.

If you are mostly concerned about the larger particles and are looking to buy a HEPA filter, make sure you pay attention to the details when buying a purifier – as HEPA doesn’t always equal HEPA.

Most importantly, make sure to frequently replace the filters as living pathogens like mold stay alive and can potentially reproduce on the filter surface. With higher moisture levels and elevated temperatures, bacteria and mold growth can even populate in particulate filter media such as HEPA. Neglecting to maintain the filter may end up introducing even more pollutants into your home – and that is certainly the opposite of what we all want.

Written by