HEPA Filter: What It Is, What It Does and What It Doesn't Do

HEPA filters are one of the most widely-known methods of air cleaning. In fact, when most people think of an air cleaner, they think of a HEPA filter. However, HEPA filters - and ALL filters, for that matter - have limitations that must be taken into consideration when choosing an air cleaning unit for your home or office.

Because filtration systems (HEPA and other filters) dilute contaminated air with cleaner air, their effectiveness depends largely upon how much filtered air they deliver over a given period into a specified space. Consequently, most filtration-type air cleaners (they are NOT air purifiers because the cannot purify the ambient air of very small contaminants like viruses!) have large, often loud fans because they only clean the air they can actually filter through them. 

The History of HEPA Filters

HEPA is an acronym for High Efficiency Particulate Air Filter, which was used in U.S. military specifications beginning around World War II. The precise definition of a HEPA varies somewhat from country to country and from specifier to specifier with respect to the efficiency for a particular test method.

A conventional HEPA filter consists of a continuous sheet of a special paper-like, glass-fiber filter medium which is pleated into a "V" configuration with corrugated aluminum separators between the pleats. This forms the filter element, which is then bonded into a rigid frame using a special polyurethane compound. Standard filters are produced in a range of face dimensions and in two standard depths of nominally 150 mm and 300 mm.

Drawbacks to HEPA Filters

HEPA filters cannot be cleaned to remove particulate and dust loading and must be replaced as a complete assembly, often at significant yearly cost. As the particle load increases, so will the resistance to flow and hence the pressure drop across the filter. In some applications, uneven filter loading will cause non-uniform airflow through the filter and decreased effectiveness. Additionally, inexpensive HEPA filter systems often do not seal the filter chamber properly, so contaminated air simply passes through the holes and back into the ambient air.

Some manufacturers will void your warranty on filtration systems if you do not replace the filter according to a very specific schedule, and most will not cover damage caused to the unit by clogged filters, which can cause the fan motor to burn up.

Even the larger HEPA air filters cover only a single room, or at most a small apartment. This is because in order for the air to be cleaned, it must pass through the filter. As a result, they can only clean the air that is nearby. While some filtration systems do incorporate flimsy charcoal or other filtration media that can absorb odors, they tend to have little effect on odors and virtually none on bacteria, viruses, germs and fungi like mold.

Other Disadvantages to Filtration Systems

  • HEPA filters are extremely fragile and can easily be damaged during installation, cleaning, and even when the unit is moved. HEPA filters should be tested at least annually. Replacement filters can cost as much as $200 (average is $75 - $150). Many air cleaner brands using HEPA filters now require that you change the filters at least once and often twice a year in order to validate the unit's warranty. 
  • HEPA units are usually loud - often sounding like a window air conditioner. Some even sound like small lawnmowers!
  • HEPA filters are costly to operate - from $100 - $300 annually in energy usage. Filter-less air purification devices cost, on average, approximately $30 to 50 per year to operate.
  • HEPA filters may cost less "up front," but actually purify less air, less effectively. Cost per square foot of filtration with a HEPA unit ranges from .35 cents to as much as $1.10 (or more); filter-less air purifiers units average .18 - .25 cents per square foot (not including electricity costs).

A key point to consider is that HEPA filters are simply that -- filters -- and are designed ONLY to FILTER larger (0.3 and above) micron-sized particulates from the air, and they can do it quickly. It is true that they can remove mold spores and bacteria from the air, but unless the filter is treated with an anti-microbial substance -- which is often, in itself, a contaminant -- the still-living microbials continue to grow and multiply on the HEPA filter. And when you pull out the filter to change it, guess where those microbials go.

Some air cleaner models offer optional filters for smoke and odors, but these simply trap chemicals and odor vapors in activated charcoal or carbon, and are not very effective unless they have a sizeable carbon, like in the Airpura models. However, it is nearly impossible to know at what point the carbon becomes saturated and can no longer absorber chemicals and odors.

By contrast, filter-less air purification devices based on Germicidal UV technology, like the Air Oasis, oxidize odors and vapors, removing them permanently, and they are effective on even microscopic particulates, bacteria, and viruses as small as .001 microns (many viruses, herbicides and pesticides are that small).

HEPA filter effectiveness significantly diminishes as the particles become smaller. As particles become very small, they cease to behave so much like particles as they do gas phase molecules. It is difficult to tell whether such small particles are actually suspended in air (particles) or diffused throughout it (gas or vapor). The bottom boundary where particles act as true particles is about 0.01 micron. The normal theory of separation does not apply to particles below this size and removing them from air requires techniques reserved for gaseous materials, like the Air Oasis technology. Particles above 0.01 micron are usually considered to be filterable. Particulates smaller than 0.01 include pesticides, herbicides, some atmospheric dust and nearly all viruses. Plus HEPA filters do not remove gases or VOCs (volatile organic chemical) off gassed from most new carpeting, building materials, furniture, etc.

To see the actual micron size of common particles
found in your home Click Here

We offer two brands that include HEPA filtration in combination with other technologies. Surround models are great for residential applications, while Airpura are excellent for larger spaces and commercial applications:

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