HEPA Air Conditioner Filter

The use of HEPA air conditioner filter is becoming more important as the consumers demand for better indoor air quality. HEPA is an acronym for High Efficiency Particulate Air, High Efficiency Particulate Arrestance or High Efficiency Particulate Absorbing.

In the past, these filters were used in clean room technology and pharmaceutical industry but these days their used have been expanded to households, offices and other applications that require clean air.

This is because a lot of households pollutants such as mold, dust, pollen, chemicals in the air, bacteria, viruses and odors are the causes of respiratory conditions. The good news is that these pollutants can be captured by good HEPA filters.

Particulate Matter (PM) Endangers Our Health

In most densely populated cities or industrial areas, the quality of air has been a major concern to the general population. Sources of pollution include pollutants from automobiles, factories, power plants, fires, construction sites, dirt and dust. These pollutants are generally divided into two categories namely PM10 and PM2.5.

PM10 is classify as inhalable particulate matter that is 10 microns and below whereas PM2.5 is 2.5 microns and below. These pollutants of different sizes are a health hazard when inhaled into our respiratory system. 

Therefore, many types of filters have been used to filter out there pollutants from the air to prevent them from circulating. One of the way is to use mechanical filters to filter out the PM, of which HEPA filters are the most effective. 

Basics of HEPA Air Conditioner Filter


Based on the definition of U.S. DOE, a true HEPA filter is able to remove 99.97% of microbes, dust, bacteria and any other particulate with a diameter size of 0.3um. The 0.3um or 0.3 microns in this case is also known as the most penetrating particle size or MPPS. MPPS is the particle size of which the filter has its lowest arrestance.

This size is the ones likely to penetrate the filter which it can capture with 99.97% efficiency.  Particles that are bigger or smaller than 0.3 microns are captured with efficiency higher than 99.97%. This means most microbes and pollutants in the air can be captured using this filter.

HEPA Filter


The HEPA filter is made of pleated randomly arranged fiberglass with the fibers typical diameter between 0.5-2.0 microns. Unlike sieving process, the particles are trapped based on diffusion, interception and impaction mechanisms.

  • Diffusion is the mechanism in which smaller particle less than 0.1 microns collides with other particles resulting in loss of speed. As a result, it wanders randomly(Brownian motion) and is trapped on the filter fiber.
  • Interception is the mechanism in which the particle, usually more than 1 microns follow the stream of air and adhere to the filter fiber.
  • Impaction occurs when the bigger particle travelling at high speed hits the fiber directly and trapping it.

Filtering Gasses and Odors

The indoor space many times are polluted with volatile organic compound gasses, chemical vapors, smokes and other odors. In order to filter out these harmful gasses which the HEPA filter cannot do, granular activated carbon or carbon cloth is used in addition to the HEPA filter. 

Air Flow Requirements

When changing a non-HEPA filter to a HEPA filter, take note that the air flow requirement needs to be recalculated by the technician as inadequate air flow will cause problems to the heat exchanger. During cooling operation, the coil freezing problem may occurred. Similarly, overheating may occurred during heating operation in winter.

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