High-efficiency particulate air (HEPA) filters were invented in the 1940s during World War II. The US Army Chemical Corps and National Defense Research Committee engineers designed them to eliminate radioactive materials from lab environments. Consisting of a mat composed of randomly arranged fibers, HEPA filters are highly effective at filtering out pollutants such as dust, pollen, pet dander, and bacteria. Their unique capabilities make HEPA filters suitable for use in a variety of applications, from residential air purifiers to industrial and medical settings.

How Do HEPA Filters Work?

To qualify for the HEPA designation, a filter must be able to trap at least 99.97% of particles as small as 0.3 microns. HEPA filters use multiple layers of fine, randomly assembled fibers (usually made of fiberglass) as a filtration solution. These densely packed fibers form a maze-like structure that captures particles that flow into the filter. HEPA solutions engage a filtration process that involves three primary mechanisms: interception, impaction, and diffusion.

Interception handles mid-sized particles passing through the air stream; they stick to any fibers they come into contact with. Impaction deals with particles greater than 1 micron in size and refers to particles entering the filter, colliding with a fiber, and then embedding themselves within said fiber. As a result of embedding themselves in the surface, the particles cannot disperse into your air.

Diffusion captures the smallest particles, typically below 0.1 microns. These tiny particles move more erratically than their larger counterparts. Particles with this motion characteristic are more likely to connect and stick to the fibers within the filter during the diffusion process.

Which Particles Do HEPA Filters Capture?

HEPA filters can remove most airborne particles to significantly enhance the quality of your indoor air. One of the primary advantages of a HEPA filter is the breadth of what particles it can remove. When looking at HVAC system filters, you’ll see various MERV ratings that indicate what they can catch; for example, filters rated as low as MERV 2 can catch pollen, but you need to go up to MERV 13 to start to remove pet dander from your air. HEPA, being at MERV 17 or more, can catch quite a few types.

Pollen is one type, as you might think considering other filters can remove it. Pollen consists of microscopic grains from plains that trigger seasonal allergy and hay fever symptoms in many people. Similarly, HEPA filters also catch many kinds of dust, which can irritate your respiratory system as well.

Speaking of dust, dust mites are another common allergen. They live in your bedding, mattresses, upholstered furniture, and other dusty areas of your home. These invisible arachnids thrive on household dust and can lead to respiratory issues if left unchecked.

Pet dander is an issue for pet owners. This material consists of small segments of shedding skin that fall off animals like dogs and cats. A HEPA filter is an excellent way to reduce pet dander indoors, a significant concern for guests and household members who suffer from pet allergies.

HEPA filters, like other filters with higher MERV ratings, can also trap mold spores, the reproductive particles from any mold present in your environment. Mold spores can cause uncomfortable allergic reactions in many while exacerbating asthma conditions. However, unlike many other filters, HEPA filters help eliminate bacteria, reducing the risk of infections. They can even capture some types of viruses, but they are most effective when those viruses are encased in the droplets that you emit when speaking, breathing, and sneezing.

Tobacco smoke is another toxic air contaminant that HEPA filters are highly effective at mitigating. Tobacco smoke consists of fine particles that can lead to multiple dangerous respiratory issues, even among secondhand recipients. However, be aware that HEPA filters can’t catch smoke from conventional combustion (such as fireplaces or furnaces), nor can they remove volatile organic compounds (or VOCs), which are airborne chemicals that step from a variety of sources.

What’s the Difference Between True HEPA and HEPA-Type Filters?

When it comes to selecting a HEPA filter, there are a couple of different options: True HEPA filters and HEPA-type filters. These products are often confused and conflated, but they each represent two distinct filtration solutions with markedly different performance levels.

True HEPA filters are engineered to meet strict industry standards established by the U.S. Department of Energy. These filters must certifiably capture at least 99.97% of all particles that are 0.3 microns in diameter. This size range covers dozens of common air contaminants, including most allergens, dust mites, and mold spores. The high-efficiency rating of a True HEPA filter means that it is suitable for use in medical facilities, laboratories, and homes that require optimally purified air.

HEPA-type filters aren’t actually HEPA filters at all, as a filter can either be HEPA or not. Instead, anything labeled HEPA-type or semi-HEPA still works similarly to HEPA filters but will not be able to perform to the same degree. They’re not required to meet the same strict government regulatory standards as True HEPA filters. This filtration solution does, however, still capture a significant amount of particulate matter. It typically eliminates anywhere from 85 to 90% of particles as small as 1 micron.

On the downside, this means the filters will miss many of the smaller particles that a True HEPA filter would otherwise trap. HEPA-type filters are more useful for general air cleaning applications. They shouldn’t be relied upon in critical environments like hospitals with stringent air purity requirements, however.

Selecting the Right HEPA Filter for Your Needs

Before choosing your next filter, you’ll need to assess your air purification requirements. This process typically begins with an evaluation of the size of the area you intend to purify. Large rooms demand substantially larger units with higher Clean Air Delivery Rate (CADR) values. A 240 CADR, for example, is sufficient to cover a 360 square-foot room and efficiently remove its airborne particles.

Choosing the right filter also requires a look at your specific health needs. Do you suffer from allergies or asthma? How serious are these conditions? Do you own a pet, and is anyone in your household allergic to it? If you’re currently managing these symptoms and they’re easily triggered or if you display a lengthy history of battling respiratory issues, then you may want to opt for a True HEPA filter. A recent study published in the Journal of Allergy and Clinical Immunology found that using a True HEPA filter can substantially lower indoor allergen levels and reduce symptoms in those suffering from respiratory illnesses.

However, you also need to check your HVAC system, as most aren’t compatible with HEPA filters, which will reduce airflow and strain the system. If your system can’t handle HEPA filters, you may be able to install one in a different area than your intake vent, or you can get an individual air purifier.

Improving Your Indoor Air Quality With a HEPA Filter

HEPA filters offer a great way to eliminate harmful air contaminants. They can also help provide allergy relief and improve asthma management while reducing exposure to viruses and bacteria. At Markool Heating & Cooling, we offer a complete spectrum of indoor air quality solutions, like duct cleaning and guidance on choosing a suitable HEPA filter. We also provide a comprehensive range of expert HVAC and plumbing services to our valued customers in Frederick, MD. Ask us about our maintenance plan!

For more on our indoor air quality solutions or to schedule your free initial consultation, contact us at Markool Heating & Cooling today!

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