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 Filters
One of the terms you will often hear when researching air purifiers is HEPA filters. This is a special type of pleated filter that is rated to remove 99.97% or more of particles that are 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 VOC’s 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 the HEPA filter but will be captured by the activated carbon or another technology. Essentially, a HEPA filter 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. Most true HEPA filters are rated 17 or higher. 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...
Fiberglass
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 HEPA 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 HEPA fitler 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; particles that are too small to be captured even by HEPA filters. 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
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).Technologies that Supplement Air Filters
Filters can be highly effective for removing contaminants, but even the best filters can use a little help to remove the smallest particles. Fortunately, there are a few technologies that are used to enhance filtration.UV Light Exposure
This is one of the most common technologies that enhances air purifier performance, and when used in tandem with a HEPA filter, it can create some of the best air cleaning possible. UV light is a common tool used in both home and commercial air purification. The filter will capture large contaminants, while the UV light can be used to destroy organic matter, such as mold spores, bacteria, and viruses. While UV light’s ability to destroy viruses and bacteria needs more research, there is strong evidence for its effectiveness against mold spores. We use a UV-C light in our Finn air purifier.Electrostatic Precipitators
You could easily argue that electrostatic precipitators are a form of filtering, but because they use an electric charge, not the material itself, to trap contaminants, we’re categorizing it outside of filters. Essentially, electrostatic precipitators pull in air, give it a charge, and use static cling to hold airborne particles in place. In many cases, the air goes through a filter before and after it goes through the electrostatic phase. However, electrostatic precipitators release a small amount of ozone, so they are generally only used for industrial applications, not in-home use. They are commonly found in industrial smoke and steam stacks, helping them release fewer particles into the air.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
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 HEPA 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 HEPA filter made from synthetic materials.Mold: HEPA Filter 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 HEPA 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 HEPA filter with UV light like our Finn air purifier to keep mold from finding a place to grow.
Asthma: HEPA Filter 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 filtration and some form of activated carbon will be able to remove your allergens. The HEPA 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 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 a HEPA filter and an activated carbon filter. These two filters will help remove both the visible smoke, which is largely accomplished by the HEPA filter, and the odor, which will mostly be removed by the activated carbon.Bacteria, Germs, and Viruses: HEPA Filter with UV Light
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
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 standard HEPA 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 HEPA filter should meet your needs if dust is the major concern.Odor Removal: HEPA Filter with Activated Carbon
Removing foul, offensive odors from the home can be difficult, but the best strategy is using a HEPA filter supported by an activated carbon system. Activated carbon is highly effective for removing the microscopic material that makes up the odor. A HEPA 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 HEPA filter with activated carbon can remove the odors and create long-lasting freshness.
