HEPA Filtration

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!) 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. 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 charcoal or other filtration media which can absorb odors, they have little effect on odors and virtually none on bacteria, viruses, germs and fungi like mold.

Other Disadvantages to HEPA Filters

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).
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. Air Oasis units cost, on average, approximately $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); Air Oasis 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, assuming the filter is properly seated and sealed. Some models offer optional filters for smoke and odors, but these simply trap odor vapors in activated charcoal and are not highly effective. Air Oasis Units actually oxidize odors and vapors, removing them permanently, and Air Oasis units are effective on even microscopic particulates, bacteria, and viruses up to .001 microns.

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. 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.

Check this chart to see the actual micron size
of common particles found in your home.

Many HEPA filters on the market now require that you change the filters at least once and often twice a year in order to validate the unit's warranty.

HEPA filtration, in conjunction with other air purification technologies, is used in the following air purifier models:

We also carry a maintenance-free air cleaner that uses heat sterilization for the destruction of particulate: Airfree Air Sterilizers.

Air Oasis's Filterless Air Purification technology uses a proprietary, patented Photohydroionization™ (AHPCO) technology that creates oxidants (hydro peroxides, super oxide ions, passive negative ions hydroxides and ozonide ions) to seek out and destroy odors and contaminants throughout your home. Air Oasis's In-Duct units use your HVAC system ductwork to provide whole-home purification. (AC systems also remove beneficial negative ions from the air; Air Oasis units replace them, giving you better sleep quality, enhanced mood and superior air purification).

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