Filter Technology

Filter Technology

There are many methods and technologies used to clean the air you breathe. Many terms sound alike and manufacturer specifications and claims can be very confusing and sometimes misleading. We will “clear the air” about these different types of filtration to help you make an informed decision about the type of air cleaner that will work best for your specific needs. We will also provide information on each of the several types of filtration, the efficiency level, benefits and drawbacks of each.

Key Factors To Consider:


Filters are often rated at a percentage (i.e. 99% effective). The important factor is the particle size the filter is capable of removing from the air. Particle size is measured in microns (1/24,500th of an inch). Common particles include allergens, dander, dust, and bacteria that range from 10 microns to .01 microns (shown in table below).  A 99% efficient filter may only be efficient on particles 6 microns or larger. Carefully choose a filter based on your specific needs.

Air Movement

Air movement rate, measured in cubic feet per minute (cfm), is an important factor to consider. Effective air cleaners should have enough capacity to clean a room at least 2 – 4 times each hour. Even the most efficient filter does little good if it doesn’t move all the air in a room through the filter. A 20’ by 20’ work or living space can efficiently and effectively be cleaned by a model with a 210–275 cfm rating.

Technology or Filtration Type

The technology or filtration method you are considering is important based on the pollutants you wish to remove from the air. The following chart explains more about the different technologies along with key benefits and drawbacks of those filtration types. See the definitions of these technologies under the chart below.

Efficiency Range
Particle Size
Fiberglass Media
3 – 5%
0.3 – 1 micron
Very low efficiency
Electrostatic Media (No electric charge)
15 – 30%
0.3 – 1 micron

Relatively inexpensive

Some use washable filters

Efficient only on larger particles

Some require replacement filters

Electret Media (Electrically charged)
40 – 90%
0.3 – 1 micron
High efficiency on large-medium size particles
Low efficiency on smaller particles
Medium Efficiency Media
35 – 60%
0.3 – 1 micron
Low airflow resistance
Require replacement filters
High Efficiency Media
60 – 95%
0.3 – 1 micron
High efficiency on many smaller particles

High airflow resistance

Require replacement filters

HEPA Media
0.3 – 1 micron
High efficiency on many smaller particles

High airflow resistance

Require replacement filters


Ozone Generator
(emission of the highly reactive molecute-O3)
inconclusive testing information
0.3 – 1 micron
Ideal for removing odor after fires

No particle collection

May irritate asthma

Considered dangerous by the EPA and OSHA


(negatively charged ions)
inconclusive testing information
0.3 – 1 micron
Relatively low cost

No particle collection

Larget particles may be


Electrostatic Precipitator
Up to 97%
0.01 microns

High efficiency on many smaller particles

Washable and reusable filters

Filter must be maintained

Dirty filter decreases efficiency


Air Purification Terms

Media Filters are commonly made from cotton or synthetic woven materials. The filter fibers catch particulates as air is pulled in by the circulating fan. Higher efficiency filters produce higher airflow resistance. Tightly woven filters capture more (and smaller) particulate but also allow less airflow.  As more particles are captured in the filter, airflow resistance increases. As a result, Media filters must be changed regularly to maintain optimum efficiency.

Electrostatic Media is prone to static charge. These filters, usually made from plastic fibers, generate a static charge as friction is generated by airflow. Electrostatic media is generally loosely woven allowing for low airflow resistance, but has lower efficiency on smaller particulates as a result. Electrostatic media filters must be changed or cleaned regularly to maintain system efficiency.

Electret Media is the same concept as electrostatic media, but is charged prior to installation.  These filters obtain a moderate efficiency on smaller particles than the electrostatic media. Electret media filters must be changed or cleaned regularly to maintain system efficiency.

Ozone Generators do not utilize filters. These machines emit highly reactive Ozone (O3) molecules into the air to dissipate airborne pollutants. An ozone generator is considered to be a hazardous workplace chemical by OSHA and is considered an air pollutant by the EPA. Ozone may also be harmful to individuals with asthma.

Ionizers also do not use filters but operate on electrostatic attraction. The unit emits negatively charged ions from a needle-like point that attach themselves to airborne particles. They are then attracted to positively charged items or surfaces such as wall and furnishings.

Electrostatic Precipitators operate using electrostatic attraction to collect particles to a filter cell. The collection plates within the filter cell are charged alternately charged with positive and negative ionizing wires. This allows for low airflow resistance while remaining highly effective on small airborne particles. Electrostatic air cleaners become less effective as the filter cell collects these particles.  The electronic collecting cell must be cleaned regularly to maintain maximum efficiency.