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Clean air, year round.

by Ed Grabianowski

You naturally want clean air in your home, yet the levels of indoor air pollutants can be 2-5 times higher than outdoor levels. If you or someone in your family has allergies or asthma, a house full of airborne particles like dust, dander, mold or pollen allergens could be a real problem. In addition to regular cleaning and adequate ventilation, using an air purifier can help to make your home as allergen-free as possible.

A common air purifier used to control levels of airborne particles is an electrostatic air filter unit, which generates electric fields to trap particles (called an electrostatic precipitator in industry terms). Electrostatic air cleaners promise to pull dust and other particles out of the air with a clever trick of electromagnetism. They can be used in portable air cleaning devices or installed in the ductwork of home HVAC systems. But there are serious questions about how effective electrostatic air filters are, and whether they might actually give off more harmful pollutants than what they remove from the air. When looking into electrostatic air filters, a good starting place is to take a closer look at how they work. They have limitations and drawbacks, as well as some situations where they might be effective.

Science diagram of how an electrostatic air filter works

Air first passes through an ionizing section, where an electric charge is applied to particles. Charged particles then attach to oppositely-charged metal plates.

Science lesson: How electrostatic air filters work

They might seem complicated, but the actual science behind electrostatic air cleaners is intuitive. Electrostatic air filters ideally work like magnets for dust and any other particles floating in the air.

Think of how the positive and negative sides of magnets attract each other. This principle is applied to airborne particles and plates within the air cleaner. If the particles passing through a filter are given an electrical charge, and you place a couple of plates nearby with an opposite charge, the particles are pulled toward the plates and stick to them. Ideally, many of the particles floating in your home would then be stuck inside the device and the problem of indoor allergens could be reduced.

The same principle of electrostatic attraction, by the way, is what makes your hair stick up if you rub a balloon on your head in dry weather. The balloon strips electrons from your hair, giving the balloon a negative charge and your hair a positive charge. Your hair, which has very little mass, then gets attracted to the balloon and sticks up.

Do electrostatic air filters actually work?

Answer: it depends. Electrostatic air filter devices do work fairly well to filter allergens from the air, because they filter particles like dust, pet dander, or mold, which are the usual suspects when it comes to allergies. However, their effectiveness depends on the type of pollutant you are looking to remove from the air, as well as the conditions of the home environment and the device itself.

The EPA uses four standards of measure to determine how well an air cleaner can remove particles from the air. The one that applies here is called the atmospheric dust spot efficiency test, which measures how well the filter can remove fine airborne dust particles from building up on surfaces. The agency reports that electrostatic precipitators have an efficiency of up to 98 percent according to this test (if the air passes through the device slowly), mainly because they can remove fine particles. However, this high initial efficiency depends on if the filter is clean. Efficiency will reduce as particles get loaded on the collector plates, or the airflow velocity increases or becomes less uniform. It is good to keep in mind that these tests are conducted in controlled laboratory settings that may not reflect real-life conditions.

You should also know that filter efficiency depends on the size of the particle. For an electronic air cleaner, the large particles are given enough charge for them to be captured well. Very small particles are also charged well. But small particles in the mid-range within 0.1 to 1 micrometers are not charged as effectively and do not collect as well on the plates. This means that electrostatic precipitators cannot filter the air of all particles at the same efficiency level–it may depend on the size of the contaminant.

Study results in real-world environments differ when it comes to the collection efficiency of electrostatic precipitators. One study by Agrawal et al. (2010) found that “an air cleaner with electrostatic filters removed larger HDM particles of sizes (10-12.5 µm) within 30 minutes and markedly reduced the concentration of smaller particles (2-10 µm) within 60 minutes.” With 30 minutes of use, the electrostatic air cleaner removed 60 percent of the airborne particles in the test chamber. However, another study by Rim et al. (2014) found that removal efficiency for an electrostatic filter was under 10 percent. It is important to note that in both tests, particle removal was greatly enhanced by the use of a pre-filter.

Now that you know a little more about how electrostatic air filters work in principle, here is how they are used in real life. The term “electrostatic air filters” can mean one of two things–an air purifier unit that uses electricity to charge particles, or a disposable filter panel that is usually placed in a heating, ventilation, and air-conditioning (HVAC) system.

electrostatic air filter article - replacing furnace filter

Electrostatically-charged fibers

You may be searching for the kind of “electrostatic air filter” that is a reusable filter medium. These are filter panels whose fibers are made from electrostatically-charged material. This is a reference to the filter medium and is separate from the category of electronic air cleaners that use an external power source.

Electrostatically-charged filters are considered “flat” filters, as opposed to “pleated” filters like HEPA filters. The difference is that if the fibers are electrostatically charged, then particles that come into contact with the fibers may be attracted and stick to the filter, instead of being trapped within the fibers (as is the case with a HEPA filter).

An electrostatically-charged panel filter is typically installed directly in your HVAC system and is made with coarse fibers. Dust and other particulate pollution in your home that pass through the filter may be attracted to the fibers and stick to them. These filters are often cheaper than other mechanical filters like HEPA because the coarse fibers are easier to manufacture. The main problem with them is that as the fibers become coated in dust, they become insulated and cannot attract particulates as well as before. Eventually they stop working. These filters can be washed and reused, however.

Electrostatic precipitators

Electrostatic air cleaners, on the other hand, also called electrostatic precipitators, are the focus of this article. The units themselves can be portable, or they can be installed as part of your HVAC system. They use the principles of electromagnetism to attract particulate pollution and require an external power source to transfer an electrical charge to incoming particles and to electrically charge a plate to collect the incoming particles. The section where the air cleaner first draws the air inside is called the ionization section (an ion is a molecule that has an electric charge because it has lost or gained electrons) and is where pollutants are given a charge. Then the particles pass by the collecting plate section, a series of flat collecting plates that have an opposite charge. The difference in charge attracts the particles to the plates very strongly, and the goal is that clean air (minus the pollutants that have stuck to the plate) comes out the other side.

Ozone problem

As they create electric fields, the biggest problem with electrostatic precipitators is that they can create ozone as a byproduct. Ozone is a chemical that at ground-level is potentially harmful to health, and may aggravate asthma and damage the lungs. A 2013 study by Rim, et al. found that continuous use of a household in-duct electrostatic air filter raised ozone concentrations to six times higher than outdoor ozone levels. The potential for electrostatic air cleaners to produce ozone should be seriously considered as you look into this option. Also, the EPA says that the chemical interactions between the ozone generated and other chemicals in the house can create fine particulate pollution.

Benefits of using an electrostatic air filter

Electrostatic air filter units remove many airborne particles of a certain size, depending on the right conditions. Yet to decide if an electrostatic filter is right for you, it is important to weigh the benefits and drawbacks. Here are some of the benefits:

Low cost: There is an initial one-time cost for an electrostatic air filter unit (either portable or installed in your HVAC system), yet there is no need to replace any filter media as the devices do not come with filters.

Washable/Reusable: Collector plates within the device can be washed off and reused.

Effective: Electrostatic filters with collector plates do a fairly good job of removing dust and other particles from the air, as long as the plates are kept clean.

Cleaning electrostatic air filter with water

Drawbacks of using an electrostatic filter

They lose effectiveness if not cleaned: The efficiency of an electrostatic filter is greatest when the collector plates are clean and not overloaded with particles. Experts recommend cleaning them every two weeks to once a month at minimum.

They only remove particulate matter: Electrostatic air filters reduce levels of particles in the air such as dust, pet dander and other allergens, yet they do not address harmful gases at all. Volatile organic compounds (VOCs) and odors from sources such as tobacco smoke, wood smoke or pets will remain in the air.

Ozone: The potential for electrostatic precipitators to produce ozone is its most serious drawback.

Our recommendation

The first step to reduce levels of allergens in your home is regular, thorough cleaning and providing enough ventilation to remove large particles that settle onto surfaces. Afterwards, it is a good idea to look into an air purifier that can effectively remove particulate pollution if your symptoms persist. Yet your chosen air purifier should not be an electrostatic air filter device because of the levels of ozone it potentially creates.

One option to address particles with high efficiency is a HEPA filter, though keep in mind that all HEPA filters need to be changed or they might become ineffective. Molekule air purifiers come with our original PECO filters which can remove potential allergens and destroy harmful gasses, bacteria, and viruses. We also offer our PECO-HEPA Tri-Power filters that combine the destroying power of PECO with the fine particle capture of HEPA.

Depending on your budget and your particular allergies, either a HEPA filter or a Molekule device may be a viable option to reduce levels of allergens in the air. The Molekule air purifier may be a better long-term investment, however, because it can remove harmful gases in addition to particulate pollution, and eliminates allergens like mold so that it can never grow on a filter. An electrostatic air filter unit, however, should be avoided because of the potential ozone it can produce.

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