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What Is A HEPA Filter | What Is A HEPA Air Purifier | Air Purifier RatingsAir Purifier Ratings

What is an Air Purifier HEPA Filter?

In this article we give an introduction to HEPA filter efficiency and how they improve your indoor air quality.

Being engineers we are pretty excited about the technical aspects of air purification.

To best explain this topic we will not get so technical.  And will use simple terms to explain what we mean.

Simply, an air purifier is a device that cleans the air. There are different types of air purifiers and they are grouped based upon how they do it.

To start it’s best to describe HEPA and efficiency separately.

HEPA Definition

HEPA stands for High Efficiency Particulate Arrestance. The “arrestance” term is sometimes referred to as “air”. So, High Efficiency Particulate Air.

HEPA is just a type of air filter. HEPA filter media is commonly made from synthetic fibers and in some cases glass fibers.

Air purifiers that have a pleated filter often refer to them as HEPA, HEPA-type or some other marketing name with HEPA in it.


HEPA Efficiency

Efficiency is simply the percentage of particles that are removed by the filter.

The Department of Energy (DOE)has a technical definition for HEPA that defines it as removing 99.97% (efficiency) of particles sized at 0.3 microns. This is also referred to as True HEPA.

A micron (or micro-meter) is one millionth of a meter. Think of this as a microscopic particle, way too small to see. These tiny sized particles are the most important to remove as they cause the most issues for you.

The larger particles do not pose much of an issue.  This is because larger particles are heavy and fall to the ground fast.  Small particles can suspend in the air for hours or days.  This is what you breathe in.


hepa efficiency


What To Look For

Where it gets confusing is that some manufacturers market their filters as HEPA.  But really just mean they have a pleated filter.

Or they may say 99.97% efficient at 1 or 2 microns. This gives the impression that it is a true HEPA filter when it is not. HEPA is based on the government standard of 0.3 micron particle size.

How can you tell if you are getting a true HEPA filter?

For one, true HEPA filters are not cheap. If your air filter costs less than $50 it is most likely not a true HEPA efficiency filter regardless of what you read.


To learn more about HEPA, please see our article on the HEPA air purifier.  Here we go into more detail about the advantages and disadvantages of a HEPA system.  And how to choose an air purifier to get clean, fresh air as well as how to size it for your room square footage.


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