What is a HEPA Filter And How Do They Work?
If you’re looking for an air purifier, you’ve most likely come across the word HEPA in relation to filtration. You may be curious what a HEPA filter is, or if you’ve heard of one, how it works. HEPA filtration is a popular and important type of air purification technology that must be studied in order to make an accurate air purifier buying decision.
What Is A HEPA Filter?
HEPA stands for High-Efficiency Particulate Air. Filters, whether for an air purifier or another purpose, come with a plethora of benefits and claims, but HEPA filters stand out because their claims go beyond mere assertions.
A true HEPA filter must be tested and certified before it can carry the label. According to standards established by the Institute of Environmental Sciences and Technology, a certified HEPA filter must trap at least 99.97% of airborne particles that are 0.3 microns or larger. This benchmark doesn’t mean the filter cannot catch smaller particles—many do—but 0.3 microns serves as the strict efficiency threshold required for certification.
What Is A Micron?
Particles range in size from ultra-microscopic to observable with the naked eye, and they are measured in microns (one-millionth of a meter). To put this in perspective:
- Human eyes generally cannot see particles smaller than 10 microns.
- Bacteria can range in size from 0.3 to 60 microns.
- One inch is equal to 25,400 microns.
How Do HEPA Filters Work?
Simply speaking, HEPA filters trap air pollutants within a dense, randomly arranged web of fiberglass fibers. Depending on the size of the particle, filtration occurs through four primary mechanisms:
- Inertial Impaction: Larger particles traveling in the airflow cannot navigate the rapid turns around the filter fibers; their momentum forces them to collide directly with a fiber and become trapped.
- Sieving: Occurs when a particle is simply too large to fit through the open spaces between the filter fibers.
- Interception: Medium-sized particles follow the air stream as it moves around fibers, but as they pass close enough, the edge of the particle touches a fiber and adheres to it.
- Diffusion: Extremely small particles move erratically (Brownian motion) as they collide with gas molecules. This wandering path increases the likelihood that they will bump into a fiber and stick.
Are All HEPA Filters The Same?
Despite popular assumptions, not all HEPA systems are identical—many manufacturers enhance base HEPA technology with proprietary features:
- Electrostatic Combination: Technologies like Blueair’s HEPASilent™ charge incoming particles with static electricity before passing them through synthetic gradient fibers to improve catch rates with less airflow resistance.
- Self-Cleaning / Antimicrobial Media: Brands such as RabbitAir utilize BioGS HEPA filters, designed to break down organic allergens and prevent bacteria or mold from colonizing the filter media over time.
- HyperHEPA Media: Specialized commercial or medical-grade systems (like IQAir) utilize ultra-dense nanofiber matrices capable of capturing ultrafine particles as small as 0.003 microns.
Indoor air pollution consistently ranks among top environmental health risks, making clean indoor air essential for long-term health and comfort. If you need assistance choosing the right air purification equipment, upgrading your filtration, or scheduling routine HVAC maintenance, contact Calvey Heating and Air today!
Joe Calvey
Joe Calvey is the CEO & Founder of Calvey Heating & Air, a leading HVAC business in San Jose, serving San Francisco and the Greater Bay Area for over 18 years.
Under Joe’s leadership, the team at Calvey Heating & Air specializes in HVAC repairs and maintenance, new system installations in custom homes, new construction, existing home upgrades, and light commercial HVAC work.