1. Knowledge Center
  2. Articles
  3. The Ultimate Guide to HEPA

Your Ultimate Guide to True HEPA (H13) Filters 

These days, as we prioritize health, many of us find ourselves spending most of our time at home. That means the air quality in your home is directly influencing your wellness most of the time. From your sleep to your immune system, your health is constantly affected by the quality of the air around you.

The great thing is that you have control over the quality of your home’s air. Air purifiers deep clean your home’s air day and night, so you’re surrounded by pure, clean, healthy air. It’s an easy, effective solution, and a great way to boost wellness. Clean air leads to improved sleep, stronger immune systems, and better overall health.


Why is air quality important?

Removing dangerous particles from the air in your home improves your household’s wellness. And who wouldn’t want that? 

  • According to the U.S. Environmental Protection Agency (EPA), we spend 90% of our time indoors, where “pollutants are often two to five times higher.”
  • The World Health Organization reports that air pollution causes increased premature illness.
  • And the scientific connection between air quality and sleep quality is becoming more apparent.
  • Alen True HEPA (H13) medical-grade filtration can capture 99.9% of harmful particles, down to 0.1 microns, including allergens, dust, mold, bacteria, aerosolized viruses, and a lot more.
  • After extensive third-party lab testing on airborne particle capture rates of aerosolized viruses for our True HEPA filters (something many air purifier brands don’t do), we’re thrilled to start talking about their outstanding medical-grade performance, and we’re gratified to be able to provide peace of mind through proven pure air protection.

What is a HEPA filter? 

The world’s #1 most trusted technology for cleaning indoor air, HEPA may be a household name, but most people don’t really know much about HEPA filters or how they work. We created this guide to help you learn about HEPA and discover what makes Alen True HEPA (H13) air purifiers unique.

HEPA stands for High Efficiency Particulate Air. Originally developed for atomic energy cleanrooms, the U.S. Department of Energy created HEPA to remove particles as small as 0.3 microns (about 56x finer than a human hair).

The most common HEPA misconception is that they can only capture particles as small as 0.3 microns. In fact, HEPA filters are extremely effective at capturing dangerous ultrafine particles that are much smaller.

“Filters are rated for the size they perform worst at—0.3 microns. As you get to larger and smaller particles, HEPA filters will capture closer to 100%." —Dr. Joseph Allen, Director of Harvard Health’s Building Program


Microscopic close up of HEPA material
An Extreme close-up photo of HEPA material. Courtesy of Engineering360.


How does HEPA really work?

HEPA filters are a complex mesh of tiny synthetic fibers carrying an electrostatic charge. They capture particles by trapping them in the maze-like mesh, or by attracting them to the charged HEPA fibers like magnets.

Using these mechanisms, True HEPA filters capture a wide range of harmful particles:  

  • Diffusion: As microscopic particles zigzag around due to a phenomenon known as Brownian Motion, they become lodged in HEPA's maze-like fibers.
  • Interception: When an airborne particle passes within one particle's radius of a HEPA fiber, the fiber snags it, trapping the particle in the filter.
  • Inertial Impaction: Larger particles collide with HEPA fibers as they're drawn through the filter, becoming trapped.
  • Electrostatic Attraction: An electromagnetic charge adheres particles to the HEPA fiber. Smaller fibers with greater charge coefficients trap smaller particles.

 Diagram explaining the physics behind HEPA filtration

How HEPA captures particles. Image courtesy of Engineering360


Can HEPA filter out germs like mold, bacteria, or viruses including COVID-19? 

Yes. It’s specifically a filter’s HEPA material that captures these particles. According to independent lab testing, Alen True HEPA filters can capture 99.9% of particles down to 0.1 microns, including aerosolized viruses. However, according to the most current scientific data, those trapped virus particles die or lose infectiousness within 72 hours.

Virus particles range from .070 - .125 microns. Testing also demonstrated over 99% particle removal efficiency throughout the entire COVID-19 range down to 0.06 microns.

We advise against removing, cleaning, or otherwise touching a purifier filter while anyone in the household believes they may be infected with COVID-19, since those trapped viruses, though captured from the air, may still be infectious if spread.

Graph of test data showing Alen air purifiers remove COVID-19 quickly
Independent test results show over 99% removal of live COVID-19 proxy virus particles from a 1,050 CuFt chamber within 20 minutes.

What’s the best way to filter smoke? How does a carbon filter work?

Activated carbon is kryptonite for smoke. Many Alen filters include a powerful layer of activated carbon (more than any key competitors) to absorb smoke. The filter’s HEPA material captures dangerous fine particulate matter in smoke that can trigger serious respiratory problems. Microscopic fractures in the activated carbon acts as a sponge, absorbing harmful chemical gasses found in smoke, including Volatile Organic Compounds (VOCs).


Activated carbon pellets used in a HEPA air purifier filter

Alen uses more activated carbon pellets like these inside our HEPA filters to remove harmful gasses and toxins from the air. 

What is True HEPA (H13) and what makes it “medical-grade”?

The True HEPA label tells you: this filter can capture at least 99.97% of airborne particles as small as 0.3 microns. Every filter for Alen’s current line of purifiers exceeds this standard! Our filters capture 99.9% of airborne particles as small as 0.1 microns (according to independent lab testing) offering superior protection against common allergens and asthma triggers, plus harmful fine particulate pollutants and microscopic pathogens that can penetrate deep into lungs.

Because this quality of HEPA filtration is used in healthcare settings, including operating room and labs, our True HEPA (H13) filters are known as “medical-grade.”

Why does “medical-grade HEPA” matter?

Better filtration means fewer damaging ultrafine particles, which are created by forest fires, viruses, vehicular and power plant emissions, tobacco smoke, and synthetic sources such as toner pigment. According to the American Lung Association, airborne ultrafine particles can infiltrate the bloodstream, where they can cause serious and lasting damage.

Air pollution is already blamed for more than 7 million deaths per year by the World Health Organization. Protection from ultrafine particles is more essential for wellness than ever, with an airborne COVID pandemic that continues to grow, and wildfire smoke affecting people thousands of miles away.

What makes Alen True HEPA (H13) better?

Coverage (and quietness). What good is medical-grade filtration if it’s only cleaning a small bubble around your purifier? Alen purifiers clean your entire room by moving lots of air, quietly and efficiently. Some other purifier brands may claim they offer medical-grade filtration or that they destroy harmful particles, but none can match Alen’s room coverage, efficiency, reliability, and quietness—the true measures of quality. And only Alen guarantees all of its purifiers for life.

Air purification is all about airflow and filtration within a breathing space. Air purifiers pull air across filters, where particles are captured, recirculating clean air back into the breathing space. An air purifier's effectiveness depends on how much air it’s able to circulate in that space.  

 To be effective, an air purifier must circulate air throughout your entire room.

What’s a “HEPA-type” filter?

Sometimes also called as HEPA-like or HEPA-style, HEPA-type filters do not meet the DOE's HEPA standard. These HEPA-type filters only capture 99% or less of airborne particles at or above 0.3 microns. 


Do I need a True HEPA filter?

If you care about improved overall wellness, better sleep, and relief from allergies and asthma, then True HEPA is definitely important. True HEPA is especially effective at capturing harmful ultrafine particles which can include bacteria, viruses, and dangerous particulate pollution.

According to The American Lung Association, "ultrafine particles are smaller than 0.1 microns in diameter and are small enough to pass through the lung tissue into the bloodstream, circulating like the oxygen molecules themselves. No matter what the size, particles can harm your health."

In 2019, Alen transitioned to True HEPA (H13) filters in all of our new purifiers. The Alen BreatheSmart FLEX Air Purifier, our most economical BreatheSmart purifier, comes standard with a Pure True HEPA (H13) filter, and offers four upgraded True HEPA (H13) filter options that are customizable by concern, from tough odors to smoke and pollution.  


Alen BreatheSmart FLEX True HEPA Air Purifier From $349

Shop Now


How can I improve my filter’s performance?

Alen's True HEPA enhancements include features or add-ons to improve True HEPA filter performance:

  • Prefilters: Providing an extra layer that catches very large particles before they get to the filter, prefilters extend the life of your True HEPA filter, allowing it to capture only the smaller, more dangerous particles. Prefilters can be vacuumed to extend filter life and enhance purifier performance.
  • Odor Control: Alen's proprietary nontoxic additive eliminates odors at the molecular level. Neutralize odors from pet accidents, litter boxes, sweaty clothes, diapers, and more.
  • Activated Carbon: Tiny fractures in activated carbon trap toxic VOC pollutants, removing them from the air while also reducing troublesome household or smoke odors. 

How do I choose a True HEPA air purifier?

Even the best True HEPA filter is only as effective as the air purifier it accompanies. When selecting an effective, livable, reliable air purifier, the two most essential factors to consider are ability to move air and quietness.

Here are some of the most relevant metrics to help you as you make your decision:

  • Clean Air Delivery Rate (CADR): Much like horsepower in a car, CADR measures a purifier's ability to circulate clean air throughout a room. CADR is measured in Cubic Feet per Minute (CFM). With CADR and your room dimensions, you can calculate Air Changes per Hour (ACH). Harvard Health recommends 4-6 ACH to remove airborne virus particles. More on that here.
  • Coverage Area: Measured in Square Feet (SqFt), this metric represents the maximum area a purifier can cover when operating on its highest (and loudest) speed. Be sure to choose a purifier that offers a larger coverage area than you need, so you can operate it at lower and quieter speed while still effectively cleaning all the air in the room. Most purifiers state room coverage in two cycles per hour (every 30 minutes).
  • Decibels: A measure of how much noise the purifier makes. Be sure to note sound levels on its highest and lowest speeds, because you'll likely utilize both on different occasions to keep your room’s air clean.
  • Efficiency: Always shop for ENERGY STAR® Certified purifiers. Most air purifier makers (including Alen) recommend continuous 24/7 operation, so power usage matters.

Many powerful air purifiers can achieve high CADR but are extremely loud. Other purifiers create less noise because they move less air, only purifying a small area of your room.  An ideal purifier is one with more than enough coverage for its intended room, that’s also quiet and ENERGY STAR® certified.


Alen HEPA Air Purifiers for the Home

Shop Now


We hope this guide has been helpful. At Alen, we believe wellness depends on pure, clean air. If our product experts can answer any questions about True HEPA filters or finding the right air purifier for the rooms you use most, we'd love to hear from you!

Please contact our in-house team of air quality experts here. Or call 1-800-630-2396 8am–6pm CST!

Leave a comment

Please note comments must be approved before they are published