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The Definitive Air Filter Guide

With lingering air quality problems both inside and out, many people are turning to air purifiers to create healthier, cleaner air in the home. These air purifiers use numerous technologies and have many different components.

One of the most important components, however, is the air filter. Although some air purifiers do not have filters, most models do. Just like the purifiers themselves, these filters come in many different shapes, sizes, and materials. They also meet many different purposes.

Understanding how these filters work is crucial if you are going to make the right choice for your home or office. When you know the various types of filters, as well as their unique purposes, you can make a smart decision for your specific air quality needs... 

What is an Air Filter?

It might seem silly to bother discussing the definition of an air filter, but it is important for this discussion. In fact, it’s not so much a matter of what an air filter is, but what it isn’t.

An air filter is a product that allows air to pass through it, catching contaminants and holding them in place. The air that runs into the air filter may be contaminated with, say, pet dander, but the air that flows outward holds less pet dander. The trapping action is one of the most important distinctions of a filter.

Many air-purifying technologies are filters. This includes activated carbon and fiberglass, which are used to trap contaminants as air passes through the material. Other technologies, such as UV light or ionizers, do not qualify as purifiers in the direct sense, as they do not actually trap contaminants. They can be used to complement a filter, but they aren’t filters in the literal sense.

Understanding HEPA Filter Based Media

One of the terms you will often hear when researching air purifiers is HEPA. This is a special type of pleated filter that is made from HEPA filter based media that can filter out particles as small as 0.3 microns. 

Most commonly, it is made of plastic material, specifically polypropylene. However, it can also be made from fiberglass or other materials.

While 0.3 microns is incredibly small (human hair is roughly 70 to 100 microns), there are gases, chemicals, and VOCs that are even smaller. In this case, other filtering products, such as activated carbon, may be needed. Some tiny gases and particles can pass through this filter but will be captured by the activated carbon or another technology.

Essentially, HEPA filter based media removes particles, such as dust, mold spores, and pollen, to a certain standard.

The MERV Scale: An Important Way to Judge Air Filters

To fully understand filters, and to help you choose the right one for your needs, you need to understand the MERV rating scale.

MERV stands for Minimum Efficiency Reporting Value. Although the system was developed to gauge filters for heating, ventilation, and air conditioner (HVAC) systems, it is now applied to air purifiers to rate a filter’s effectiveness. They are especially important for rating large purifiers used for entire houses or large areas.

Filters and air purifiers receive a MERV rating based on a series of tests. The tests release particles into the air in a controlled environment, then pass the air through a filter. The contents are measured and a rating is given. The process is repeated multiple times to ensure accurate results.

The rating system ranges from 1 to 20, with 1 being less-effective and 20 being the best filtering possible. When you review filters, understand that the higher the rating, the more particles that filter will remove. 

There’s one important flaw to the MERV scale, at least in regards to air purifiers: the system only rates a filter’s ability to remove solid particles. It doesn’t rate the filter’s ability to remove gasses that are often found inside the home. This is because the MERV system was developed for keeping dust and large particles out of HVAC appliances; tiny household gasses like ammonia or carbon monoxide are not a concern for furnace maintenance.

This is an essential distinction, because air purifiers are extremely effective for removing gasses and other contaminants, but the MERV rating may not reflect this ability.

Different Types of Air Filter Materials

To better understand air purifier filters, let’s take the time to review some of the different materials used to filter air and trap pollutants.

While there are many different materials used, these are a few of the most common...


Spun fiberglass is an affordable and reliable resource for filtering air and trapping contaminants. Fiberglass is excellent for trapping large contaminants, such as dust and pet dander, and it often helps maintain superior air flow.

Many  high efficiency air filters are made primarily from fiberglass. Although fiberglass can be effective, it’s biggest advantage is often pricing. Compared to other filters, fiberglass filters can be more affordable, making air purification less expensive over the long term.

On the negative, glass fiber filters require more filter media than a filter that is made of synthetic material. In having more filter media, the air flow resistance, also known as pressure drop, is higher. This means the airflow through the glass fiber filter will be a little less. 

Activated Carbon

Charcoal seems dirty.

How can it possibly be used to clean air?

Actually, activated carbon, which is made from charcoal, is one of the most effective cleaning materials on the planet, and it’s been used for centuries to clean water, air, and even our bodies!

Carbon is highly porous, but it needs to be treated with heat, chemicals, and other measures to remove various elements. When treated, or “activated,” the result is a highly porous material that can remove many of the tiniest particles.

Activated carbon is considered one of the safest, most reliable air filter materials available today.

Although it can be more costly, largely because of the activation process, it is incredibly reliable, consistent, and effective. In fact, it’s not just used for air and water purification, it’s also used for decaffeinating beverages and even purifying gold.


Plastics, most often polypropylene, are durable and reliable materials that can be used to make filters, which are often washable. This creates both long-term affordability, as you don’t have to purchase new filters, as well as an eco-friendly product, as new resources are not required.

Plastic filters, often called synthetic filters, can be effective resources for removing impurities for the air, creating a cleaner indoor space.

In our EJ120 and Erik650A air filters, we add a charge to the synthetic filter fibers to give the filters a boost in performance. This gives the advantage of higher filter efficiency without an increase in the pressure drop or any impact to the air flow or noise level.

Plants: Nature’s Air Filter

If we define filters as a material that allows air to pass through while capturing contaminants, then plants are most certainly a type of air filter.

Plants absorb air through tiny pores, which are usually located on their leaves. These pores take in air and use the CO2 during photosynthesis, converting light into their food. However, while they take in CO2, they are also taking in other gases, toxins, VOCs, and other microscopic contaminants.

When used as a supplement to your purification system, a plant’s air filtering ability can add healthier air and more oxygen to your indoor environment.

While plants can clean the air of indoor air pollution related to gases, the effect is limited and plants provide no help in removing airborne particulates (dust, mold spores, pollen, etc).

Best Filters for Specific Purposes

Now that we have a broad idea of the major materials and technologies used in air filtration, let’s take a look at some typical problems and identify which filters and technologies you should use to address these concerns. 

Pet Allergies: HEPA Filter Based Media

In almost all cases, pet allergies are caused by pet dander, which is essentially floating skin cells.

It’s not the pet’s hair that causes the problem, it’s the skin cells, but pet hair can act as a vehicles, helping spread the cells throughout the home.

In the world of air purification, pet dander particles are quite large. Most pet dander is over two microns, which means a high efficiency air filter will be able to remove the vast majority of dander from the air.

If you suffer from pet allergies, and want to remove this allergen from your home, you should be able to achieve your goals with a high efficiency air filter made from synthetic materials.

Mold: HEPA Filter Based Media with UV Light

Spores from mold can also be quite large, but simply removing them from the air may not do the trick, at least not entirely.

A high efficiency air filter can be extremely effective for trapping mold, but in many cases an air purifier that also uses UV light is more thorough.

Mold spores are a biological particle (in other words, they are living), and UV light will damage the DNA, destroying the spores and keeping them from reproducing. This results in mitigation of mold and, as a preventative measure, keeps mold from reproducing, or at least keeps it from reproducing as quickly.

If you want to add an air purifier to a damp basement, consider a high efficiency air filter with UV light to keep mold from finding a place to grow. 

Asthma: HEPA Filter Based Media with Activated Carbon

If you have asthma that is caused in any way by airborne particles, you will likely want an air purifier in your home. However, the specific type may depend on the contaminants that you are allergic to.

In most cases, an air cleaner that uses HEPA filter based media and some form of activated carbon will be able to remove your allergens.

The  high efficiency air filter will remove most of the large contaminants, such as dust and pet dander, while the activated carbon can trap many of the extremely small particles.

This should be effective for removing most or all of the allergens that are giving you trouble.

Smoke: HEPA Filter Based Media with Activated Carbon

When most people consider smoke removal, they automatically think of cigarettes.

While this is certainly the common culprit, smoke can come from household fireplaces, kitchens, and even wildfires. Therefore, it’s important to have a purifier that can remove smoke, even if tobacco is not part of your household.

To remove as much smoke as possible, it’s best to have both HEPA filter based media and an activated carbon filter. These two filters will help remove both the visible smoke and the odor. 

Bacteria, Germs, and Viruses: HEPA Filter Based Media

We have to be very honest and up front on this topic: the scientific evidence for using air purifiers for sanitation, killing microorganisms, and enhancing health remains slim.

However, there is steadily-growing evidence that it may be helpful for germ, bacteria, and virus removal.

One study, conducted by researchers at the University of Colorado, found that UV light “inactivated” roughly 97% of bacteria cells captured in a filter. This gives a strong indication that it may be effective for anti-bacterial use.

A review of scientific data found that “in-room air cleaners (both with and without UV light) may be used to protect health care staff from airborne infectious pathogens such as tuberculosis, chicken pox, measles, and dessiminated herpes zoster.”

Dust: HEPA Filter Based Media

In many ways, dust is like pet dander.

In fact, if you have pets in your home, a good portion of the dust likely is pet dander.

For this reason, a  high efficiency air filter should be enough to remove the majority of contaminants from your home. It will trap most of the large floating dust and create clean air throughout your house.

Because UV light only works against living organisms (like mold spores), and because activated carbon is only needed for exceptionally small particles, a high efficiency air filter should meet your needs if dust is the major concern.

Odor Removal: HEPA Filter Based Media with Activated Carbon

Removing foul, offensive odors from the home can be difficult, but the best strategy is using a  high efficiency air filter supported by an activated carbon system.

Activated carbon is highly effective for removing the microscopic material that makes up the odor. A  high efficiency air filter alone may not be able to achieve odor removal, but an activated filter can likely help remove the unpleasant smells.

Using activated carbon for odor control is effective because it doesn’t just mask the odor, it removes it. Aerosol sprays often release harmful chemicals into the air, and provide only temporary relief. However, a  high efficiency air filter with activated carbon can remove the odors and create long-lasting freshness. 

Households with Children: HEPA Filter Based Media and Activated Carbon

We all want to provide the best environment for our children, so having an air purifier that uses different technologies to eliminate harmful contaminants is always a good idea.

When you use air purifiers with a  high efficiency air filter and activated carbon, you are taking the most comprehensive approach to fighting indoor air pollution.

This will result in excellent purification for the entire family because you are using a variety of technologies to trap and destroy contaminants. Whether you have children with allergies, compromised immune systems, or vibrant health, an air purifier can help everyone feel better.

Air Purifier FAQ

To wrap up our air filter guide, we’d like to look at some of the most commonly-asked questions. If you don’t see your question below, visit our Air Purifier Education Center or feel free to contact us and we’ll reach out to you with more information.

How often should I replace or clean my air filter?

The frequency of replacements will vary depending on how often you run your purifier and how much dust, dander, and other contaminants run through the filter. The frequency will also depend on the type of filter and purifier you have, so it’s important to check the owner’s manual and other information. Stick to the manufacturer’s recommendations for the best long-term performance. That said, you will likely have to change your filter between every six months to every two years.

Is any other maintenance required for air filters and purifiers?

Changing the air filter is the most common maintenance you’ll need to do to your purifier, but there are some things you can do to maintain quality performance. Depending on the model you have, you may need to replace parts that break or become worn out. For example, if your filter uses UV technology, the bulb may need to be replaced at some point.

How do I know when it’s time to change a filter?

For most air purifiers, there is a filter replacement indicator that gives you an alert when it is time to check or change the filter. This indicator gives you greater confidence because you know you are not using old, dirty filters, nor are you spending too much money replacing filters when it’s not needed.

What can I expect to spend on new filters?

As we’ve seen, filters can come in a wide variety of styles and sizes. As such, there is also a wide variety of prices. You can reasonably expect to spend less on “pre-filters” and more on the main filters. 

My HVAC system has an air filter. Isn’t that enough? What is the difference?

Some people assume that the air filter attached to the furnace will help remove dust from the air and create better indoor air quality. While these filters can trap large particles of dust and airborne debris, they are not intended to clean the air you breathe.

Their purpose, rather, is to clean the air that enters the appliance.

When air moves from the appliance to the living space, it travels through vents that are often dusty and dirty, picking up contaminants along the way.

Also, HVAC air filters do not catch the extremely small particles that can be trapped by advanced air purifier high efficiency filters, such as gasses and VOCs. 

For these reasons and more, you should not consider your furnace or air conditioner filter an air purifier.

Purchase Your Air Filters Online from Oransi

When you own an Oransi air purifier, you’ll have access to our complete online support system, which includes filters for every purifier well sell. Simply visit our Replacement Filters page, click on the model you own, and you’ll see a full list of available filters.

You have access to pre-filters, combination filters, activated carbon filters, and even replacement UV bulbs. We make air purifier ownership easy, so contact Oransi today for more information on our full selection of world-class air-cleaning products!

*Oransi still offers replacement filters for retired air purifiers.