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What are HEPA and MERV filters?

Updated: Apr 26

Air filters–the pesky things you have to change every couple of months that are just too easy to forget about! We all know that air filters are super important to overall air quality and consequently health as well. You may have heard of HEPA filters, but have you heard of MERV? Here, we’ll explore what exactly an air filter consists of and the difference between the two leading types of filters.

man fixing AC unit

How do air filters work?

Of course, this may seem like a pretty obvious question–they filter air! However, air filters can be a little more complex than that. Air filters are comprised of many layers of finely-woven filter mediums that progressively get denser–meaning that as air passes through the filters, particles of many sizes are trapped by the sequence of filters.

Ironically enough, air filters actually get better at filtering as more particles get trapped. The trapped particles in the filter medium act as an even more “filter”, grabbing onto particles as they pass through. Although filters may work better when particles are caught within them, the more clogged a filter becomes, the more restrictive it is on airflow, which can put a strain on your HVAC system and your electricity bill.

What’s a HEPA filter?

Probably the more recognizable name here, HEPA filters are pleated mechanical air filters. It stands for High Efficiency Particulate Air, and can trap 99.97% of particles that are 0.3 microns in size. A HEPA filter is comprised of densely woven glass fibers that create a labyrinth for any particle to have to traverse it.

How does a HEPA filter work?

With its intricate weavings, HEPA filters knock out particles of different sizes in many ways, which include:

  • Diffusion. When the smallest particles move around the maze erratically, they tend to hit and stick to the fibers easily.

  • Interception. Although the airflow carrying the particles can swiftly move across the fibers, the particles being carried aren’t as nimble and quickly get caught in the fibers.

  • Sieving. Much like a baking sieve, particles that are simply too big to go in between two fibers get caught as the air passes through.

  • Direct impaction. Larger particles, like dust a mold, simply impact and stay on the particles, as they are much larger than particles that we cannot see.

What’s a MERV-rated filter?

MERV, meaning Minimum Efficiency Reporting Value, is a rating that measures a filter’s ability to trap contaminants ranging from 0.3 and 10 microns. The higher a MERV rating, the better the filter is at trapping specific particles; however, if choosing a MERV filter, it’s important to consult a professional to find out which rating is best for your HVAC system, as higher-rated MERV filters can actually put your HVAC system under stress. With MERV ratings, you are able to find filters for your specific needs.

MERV filters have a wide array of applications based on your specific needs in your home, business, or worksite. Ranging on a scale of 1-20, MERV filters have the ability to be nearly tailored to your filtration and HVAC system needs.

When to use HEPA vs MERV?

HEPA filters are usually a very safe route, as they are able to provide an extremely high level of filtration all around. Likewise, HEPA filters are more often necessary due to specific requirements.

MERV filters are great when looking to filter for specific contaminants on worksites to protect workers. With the large range of filtering power, MERV filters can run a pretty wide gamut of their uses. Tune in later this week as we dive into specifics for Merv filters.

Call us

Have questions about filters, their differences, and which one is better for your filtration needs and specific HVAC system? Please, don’t hesitate in giving us a call here at Tri-Point Refrigeration. We’re happy to hear from you and are excited to help you along the way.

For a direct line to any of our employees ready on the line to help you, please call…(512) 651-4565 for our Austin, Texas community (806) 686-0050 for our Lubbock, Texas community. Or check out our website at

<a href="">Image by senivpetro</a> on Freepik



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