HEPA (High Efficiency Particulate Air) filters and Microns and 99,97% clean are some familiar terms being thrown around by every Air Purifier manufacturer.

Similar terms are associated with Vacuum Cleaners, HVAC systems and many other systems using HEPA filtration to improve air quality.


Most air purifiers in the market today are built around the HEPA filtration system and a combination of other more exoctic technologies like Ionization, UV Lights and activated Carbon. The primary goal of all these technologies is to achieve a level of cleanliness that would make our immediate environment free of contaminants.

Air Purifiers are designed with the purpose to provide clean air in the immediate vicinity of areas most frequently used in our homes and offices. They are a great tool for people suffering from allergies as they are able to efficiently capture contaminants above 0.3 microns.


What is a MIcron? How does a HEPA filter work? How big a space would the Air be considered clean? What should you expect not to be in the air? How long before the air quality reaches the desired level of cleanliness?

All these are questions any consumer should expect to get answers for from an air purifier company. 


A micron represents a dimension equal to one millionth part of one meter or 25,400 microns in an inch. A human eye cannot see anything below 10 microns.

Translated into everyday language:

  1. Spores: 3 – 40 microns
  2. Mold: 3 – 12 microns
  3. Bacteria: 0.3 – 60 microns
  4. Car emissions: 1 – 150 microns
  5. Pure oxygen: 0.0005 microns


HEPA filters typically work by creating impedance in the path of airflow and use the fiber to collect these particles. Finally the air that comes out is free of the bacteria, pollen, smoke and other contaminants.

This process is repeated multiple times through the filter and with every cycle the probability of a particle getting caught in the fiber keeps going higher. Hence  the figure 99.97. That represents the expected level of contaminants that would get caught in the filter.

All air purifiers use what is called the five step cleaning system with, Inertial, Impaction, Diffusion, Interception, or Sieving. Inertial, impaction and sieving being used for large particles, interception for medium and the diffusion for the smallest.


Every Air Purifier has a capacity. That is represented by the square footage of the area that it can clean in a reasonable time.

Air has a tendency to move freely and hence the air in any space is always dynamically being displaced both within the space and is interacting freely with the area outside that space through cracks, doors and windows. Hence the air purifier has to deal with a dynamic environment and any claim of clean has to  take this dynamic situation into its specifications.


The effectiveness of the Air Purifier is defined by the level of clean and time required to reach the desired level of clean.

By definition a HEPA filter is designed to restrict any particle size 0.3 microns,

That being said, the differentiation between filters is done based on the CFM (CUBIC FEET PER MINUTE) flow of air that the filter delivers as clean.


All HEPA filters use the same technology but not all air purifiers are created equal.

A good air purifier has to be effective over the desired area every time and day after day. It has to be able to clean and keep it clean in an environment that is dynamic by its nature and not very forgiving when contaminated.

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