What the Heck is a HEPA Filter?

a photo of a confused woman

You hear about them in advertisements for everything from air purifiers to vacuum cleaners, but most people do not know exactly what a HEPA filter is. The acronym stands for “High Efficiency Particulate Air.” In some circles it has a more official sound by being defined as “High Efficiency Particulate Arrestance.” However, not every air filtration media qualifies for the moniker. In order to truly be a HEPA filter, it must remove 99.97 percent of all particles that are 0.3 micrometers in size or bigger. Particles that size are up to 50 times smaller than what a person can see.

What Are HEPA Filters Made of?

The most used material is fiberglass of a specific size arranged in a mat configuration. Unlike single thickness filters one might find in a furnace or window air conditioner, a HEPA filter has its media arranged in a configuration of several mats of a specific shape and separated by very specific distances from other mats enclosed in a cartridge or container. Ones used to filter out biological pathogens are in metal containers to protect from microbial contamination of the container.

How Are HEPA Filters Used?

HEPA filtration is used by both commercial and residential customers. In commercial applications HEPA filtration is used in clean rooms where things such as microchips are made. The tiniest dust particle could ruin a microchip during its manufacturing process. HEPA filters are also used in hospitals and research facilities where the air may contain biological contaminants. Both commercial and residential applications include filter cartridges for heating, ventilation and air conditioning (HVAC) use. Standard residential HEPA filters include ones in air purifiers and some vacuum cleaners.

How do HEPA Filters Work?

The arrangement of the fibers is random on the mats. The mats are stacked and separated by separators that are often made of metal and are a corrugated shape. The size of the filter as well as the spacing between the mats is worked out mathematically to provide the optimum level of filtration based on the volume of air that will be traveling through the filter. The actual filter media stops particles in three different ways.

The first level of protection is “impaction.” This is where larger particles simply flow into the filter in a straight line with a lot of inertia and smack into the filter fibers, thereby getting stuck. The next level affects smaller particles and is called “interception.” Small particles may travel a bit farther until being intercepted and trapped by filter fibers. The next level of protection is “diffusion.” This is where very tiny particles collide with molecules. They get pushed against fibers of the filter media and then get stuck.

How is a HEPA Filter Different than Other Filters?

One of the main benefits of HEPA filtration is that performance improves as the filter gets dirty. This is completely opposite of how other filters work. Standard air filtration media performance declines as the filter begins to fill up with particulate matter. However, HEPA filters do need to be replaced when the air flow through the filter diminishes due to particulate buildup.

When the choice between a regular filter and HEPA filter is offered for any appliance, the HEPA filter will perform better. They are better at reducing particles, including everything from pollen to mold and bacteria. Mold is particularly prevalent here in the Largo, Florida region. With indoor air almost always more highly contaminated than outdoor air, HEPA filtration at home and work provides cleaner air to breathe. This is especially true for those with allergies and weak or compromised immune systems.