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The Ultimate Guide to HEPA

It's an understatement to say that we're spending more time at home these days. That has people thinking more about their indoor air quality its effects on wellness, immune health, and sleep. 

HEPA air filtration is the world's most trusted technology for cleaning indoor air. You’ve probably heard of HEPA, but how much do you know about it? Some of the weird ways HEPA air filters work might surprise you. This guide will help you understand the difference between HEPA vs. True HEPA and how to compare True HEPA air purifiers.

Why Indoor Air Quality Matters

The  U.S. Environmental Protection Agency (EPA) tells us that "pollutants are often two to five times higher" indoors while the  World Health Organization reports that air pollution is causing increased premature illness. Plus, the  scientific connection between air quality and sleep quality is also becoming more apparent. 

We spend 90% of our time indoors, according the EPA. Removing larger particles like dust and allergens as well as dangerous ultrafine particulate pollutants and germs gives us much greater control of our overall wellness. And who doesn’t want that?

What is HEPA, and how does it work?  

HEPA stands for High Efficiency Particulate Air. Originally developed for atomic energy cleanrooms, the U.S. Department of Energy created HEPA based on a particle removal effectiveness of 99.97% at 0.3 microns and above (0.3 microns is about 56x finer than a human hair).

HEPA filters utilize a complex mesh of tiny synthetic fibers that carry an electrostatic charge. Some particles are trapped in the maze while others stick like a magnet. But more about that later.

Air purification is all about airflow and filtration within your room, which you can think of like a breathing space or a box. Air purifiers pull air across filters. Particles are captured as clean air is recirculated back into the space. It's important to note that an air purifier's effectiveness depends on its ability to draw in contaminated air and circulate pure air throughout your ENTIRE breathing space.  

Alen is proud to make top-rated purifiers that do both—quietly, reliably, and efficiently.



Macro HEPA Fiber Zoom
An extreme close-up of HEPA material, courtesy of Engineering360.

What is a True HEPA filter? 

Today, filters meeting the DOE's particle removal effectiveness rating of 99.97% at 0.3 microns and above are known as True HEPA. True HEPA air filters (grade-H13) offer superior protection against common allergens and asthma triggers PLUS harmful fine particulate pollutants and microscopic pathogens that can penetrate deep into lungs.

What is a HEPA-Type filter? 

Also known as HEPA-like or HEPA-style, HEPA-type filters do not meet the DOE's HEPA standard. These filters HEPA-type filters only remove about 99% or less of airborne particles at or above 0.3 microns.  

Do I need a True-HEPA filter? 

If improved overall wellness, allergy and asthma relief, and improved sleep are important to you, then True HEPA is worth considering. 

True HEPA is especially effective at removing smaller particles that can be harmful to one's health. While HEPA-type and True HEPA filters potentially catch the same kinds of particles (dust, dander, hair, pollen, mold, and pollution), True HEPA filters are more effective at capturing 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."

At Alen, we have transitioned to True HEPA Air Filters in all of our new purifiers. The Alen BreatheSmart FLEX Air Purifier, for example, comes standard with a Pure True HEPA filter, and offers four upgraded True HEPA filter options that are customizable by concern—from smoke and pollution to pet and diaper odors.  

What else should I know about True HEPA filters?  

Many manufacturers include other features or add-ons to improve True HEPA filter performance. Below are a few examples of Alen's TRUE HEPA enhancements: 

How HEPA Really Works 

True HEPA filters capture a wide range of harmful particles above and below 0.3 microns through a combination of the following three mechanisms:  


Filtration Mechanisms Diagram
How HEPA captures particles. Image courtesy of Engineering360

How to Choose a True HEPA Air Purifier

Even the best True HEPA filter is only as good as the air purifier it accompanies. Ability to move air and quietness are the two most essential factors in selecting an effective and livable air purifier. Below are the most relevant metrics to help you compare:

Many powerful air purifiers can achieve high CADR but are extremely loud. Other purifiers create very little noise because they're not moving much air and thus only purifying a small area of your room. An ideal purifier is one with slightly more capacity than its intended room that’s quiet and ENERGY STAR® certified.

At Alen, we believe wellness depends on pure air. If our team of 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!

Call 1-800-630-2396 8 a.m. to 6 p.m. M-F & 10 a.m. 4 p.m. Saturday, email, or chat at

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