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Your Guide to HEPA Air Filters

Administration Staff

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Most people associate air pollution with the outdoors, but according to the U.S. EPA, the scary truth is that indoor air quality is often 10 times more polluted. This effect occurs because there is less ventilation indoors and therefore concentration levels are higher. A HEPA air purifier rectifies this situation by removing 99.97 percent of the particles that comprise pollution down to 0.3 microns in size. This filtration reduces pollution significantly and creates an overall healthier environment. In fact, it is so effective that it can significantly reduce allergy symptoms.

The History of HEPA

HEPA is an acronym that stands for high-efficiency particulate air. Scientists developed the technology during the Manhattan Project to prevent radioactive particles from escaping testing environments. The technology was so effective and cost-efficient that the government made it available for commercial and residential use by the 1950s. Amazingly, HEPA filtration has not changed significantly since it was first designed. The role of a HEPA air filter is to sanitize the air by removing small particulate matter. This process is crucial in hospitals, laboratories, hi-tech manufacturing environments and other areas where the removal of airborne pollutants is essential for human health and safety.

How HEPA Air Filters Are Made

HEPA filtration media is made of thick submicron borosilicate fibers that are pressed into a net-like structure. This unique design allows air to pass through but is tight enough to trap particles. The material is cut into sheets that are then folded into a pleated design. The pleats are very close together, which allows for maximum surface area. Lastly, the formed media is placed within a rigid, often metal, frame.

What HEPA Traps

In order to be a high-efficiency HEPA air filter, a filter must trap 99.97 percent of all airborne particulates down to 0.3 microns in size. A micron is one-millionth of a meter. To put 0.3 microns into perspective, consider that the typical human hair has a diameter of 100 microns. In a residential environment, the particles trapped include bacteria, dust, dust mites, mold sporespet dander, pollen and VOCs. Removing this matter from the area creates a sanitary environment and one that is conducive to easier breathing.

How Particles Are Trapped

HEPA air purifiers are not standalone devices and must work as part of an air purification system. The air purifier draws air into the system where it passes through various filter stages. Most portable air purifiers will have a pre-filter stage, a HEPA air filter stage and an activated carbon filter stage. The pre-filter is responsible for trapping the very large particles, which greatly increases the long-term usefulness of the HEPA air filter. As air passes through the HEPA filter stage, it follows the path of least resistance, and the remaining particles are trapped in what is essentially a net. For certain models of air purifiers, the air then passes through the activated carbon, which traps the contaminants that a HEPA air filter cannot, such as chemicals, gases and odors. Finally, the air is recirculated back into the living space.

Net and web metaphors are actually a simplification of what occurs within a HEPA air filter. The technology actually traps particles in four unique ways: Brownian diffusion, inertial impaction, interception and the sieve effect. Brownian diffusion occurs when air particles collide with gas molecules, which extends their path through the filter and increases the likelihood that they will collide with a fiber. Inertial impaction occurs when particles cannot react fast enough to airflow changes, which causes them to be trapped on a fiber due to inertia. Interception occurs when a particle is trapped by a fiber due to proximity and not direct contact. The sieve effect occurs when a particle is too large to pass through the hole where the air is flowing. Combined, these four mechanisms let the filter trap particles in a more efficient manner than would otherwise be possible if it were simply dictated by the porosity of the filter material.

HEPA Efficiency

HEPA air purifiers are employed wherever purified air is required, such as laboratories, hospitals and clean rooms. HEPA filters are able to trap the microscopic particles that can lead or exacerbate respiratory disorders like allergies, asthmaCOPD and emphysema. These particles include bacteria, dust, dust mites, mold spores, smoke, pet dander, pollen and viruses. No other filtration technology comes close to this level of efficiency, which is why HEPA use is so widespread nearly 75 years after its invention.

Not all HEPA is equal, however, and there are two crucial considerations: marketing and air filter quality. In order to be HEPA, a filter must trap 99.97 percent of airborne particles down to 0.3 microns in size. Many manufactures try to trick consumers by marketing inferior filters as HEPA-like or HEPA-type. Secondly, even if a filter is true HEPA, it will not be effective unless the air passes through it. A substandard air filter will actually allow air to pass around the HEPA air filter frame. Air filters from top manufacturers are designed to force the air 100% through the HEPA media, allowing no air to bypass the filter.

The Limitations of HEPA

A HEPA air filter is limited by its hole size, which for standard HEPA is 0.3 microns. Even though the HEPA filter is very dense it is not able to trap chemicals, gases and odors. Activated carbon is the most effective way to remove those substances. Therefore, most high-quality air purifiers deliver optimal air quality by using HEPA filtration and activated carbon filtration in tandem.

Air Purifier Care and Maintenance

Most portable air purifiers require an electric outlet and use a fan to force air through the system. Over time, air filters become clogged and require replacement. Most HEPA air filters will last three to five years in a residential environment. If the filter is not replaced when necessary, performance will suffer, and it can eventually cause undue strain on the fan motor, which can lead to system failure. If a HEPA air filter ever becomes damaged in any way, it must be replaced immediately because air will circumvent filtration via the defect.

HEPA Air Purifier Considerations:

  • Never settle for anything less than true HEPA — 99.97 percent down to 0.3 microns. Pay attention to the specifications, and avoid manufacturers that employ vague descriptions like HEPA-like or HEPA-type.

  • A superior air purifier is able to direct all of the dirty air through the HEPA air filter. Otherwise, the system is simply distributing the polluted air back into the living space.

  • A HEPA air filter is a significant obstruction to airflow. Therefore, a powerful fan motor is needed to create enough suction in order to ensure that the air purifier operates at peak efficiency.

A HEPA air purifier ensures easier breathing and promotes better health. Without proper filtration, the air in our homes can be ten times more polluted than the air outdoors and a HEPA air purifier is the only way to ensure that your family breathes the clean air they deserve. 

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Clean Air Plus is a veteran and family owned small business. We represent the leading manufacturers in HEPA filtration including Austin Air, IQAir, Amaircare, Oransi and Airpura. Shop online or call one of our friendly experts at 888.247.1147. We'll be happy to help.


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