The Different Types of Air Purifiers

If you think you are safe from the bevy of airborne pollutants once you enter the safe confines of your home, think again. Indoor air pollution is a major cause of concern. Regardless of how well you clean your house, air pollutants will always find their way inside via winds, pets, and humans.

Common household air pollutants, like dust, pet dander, pollen, and mold spores can trigger allergic reactions and asthma attacks when present in high concentrations. In extreme cases, these air pollutants can also cause several health problems like respiratory diseases and cancer. What’s worse is that indoor air pollution can be more harmful than outdoor air pollution because the air indoors is much more concentrated than the air outdoors. This is quite alarming, especially when you consider the hours that you spend indoors with your family.

One of the best ways to reduce the amount of air pollutants at home is to make use of air purifiers. Air purifiers were specifically designed to address the problem of indoor air pollution by using different technologies to clean the air. Simply put, air purifiers take in polluted air and release clean air back out. Like any other type of home appliance, air purifiers come in array of sizes and shapes and, although they all have the same goal of removing air pollutants, they vary in the way they do this. In order for you to know what type of air purifier would best suit your needs and your lifestyle, this article looks at the two most common types of air purifiers available – room air purifiers and whole house air purifiers – so that you can familiarize yourself with key features and make smart decisions for cleaning the air in your living space.

Room Air Purifiers

As the name suggests, room air purifiers (also known as plug-in air purifiers) are used for cleaning the air in individual areas such as bedrooms, living rooms, kitchens, or bathrooms. Normally, these types of air purifiers are only turned on when there are people in the room, but they can also be left to run all day. They vary in size: some are small enough to be placed on car dashboards, while others are large enough to take up an entire corner of your living room.

There are several types of room air purifiers, but they can be grouped into two categories:

1. Air Purifiers with Filters

Air purifiers that use filters are designed to suck in polluted air, run it through a filter or series of filters, and release clean air back out. The main principle behind this type of air purifier is to clean the air by size exclusion, removing differently sized pollutants by trapping them in different types of filters.

The following are the most commonly used filters in filtered air purifiers:


Pre-filters act as the first line of defense for your air purifier. It is in-charge of removing the largest pollutants such as hair, fur, dust, and some pollen. They are even capable of trapping small insects. Without the pre-filter, the main filter (which is usually the HEPA filter) wears out more quickly, resulting in more frequent and expensive filter changes throughout the year. Pre-filters can last a lifetime if they are cared for properly, but if your pre-filter is combined with a carbon layer, it will need to be replaced when the carbon layer stops functioning.

HEPA Filters – Allergies

True High Efficiency Particulate Arrestance (HEPA) filters are able to filter out 99.97% of particulate pollutants, such as pollen, mold, dust mites, and more, which are as small as 0.3 microns in size. Accordingly, True HEPA filters allow for a more sanitary environment and are commonly used in health facilities. Do not confuse True HEPA filters with HEPA-type or HEPA-grade filters, though, as these latter types of filters are not as efficient and are only capable of removing 99% of particles 1 to 2 microns in size or larger. In addition, one drawback to the HEPA filter is that it is not designed to remove smoke, odors, and volatile organic compounds.

Activated Carbon Filters – Odors

Activated carbon is specifically manufactured at high heat to become extremely porous and to give it a large surface area to ensure maximum absorption of volatile chemicals on molecular basis. The molecular-sized pores on activated carbon filters have high absorbency and chemical bonding. These two properties make them highly effective in capturing pollutants that are able to pass through HEPA filters like chemical emissions, gases, tobacco smoke, and other odors. This is why HEPA filters and carbon filters are best used together.

Permanent/Washable Filters

Permanent filters (also known as washable filters) are filters that do not need to be replaced. Once saturated with pollutants, these permanent filters only need to be vacuumed or washed to remove them and then used again without losing its efficiency. Permanent filters are much cheaper in the long run since they are designed to last a lifetime, but they need to be properly cared for in order to last that long.

2. Filterless Air Purifiers

Filterless air purifiers do not use any type of filter or filtration system. Instead, they rely on different types of technologies to clean the air. Often, these technologies are used in conjunction with filtered air purifiers to increase their efficiency. They are also highly efficient on their own, though, and users have found them easier to maintain because filter replacements are no longer an issue.

Air Ionizers

An air ionizer is a type of air purifier that cleans the air with the use of negative or positive ions. It releases a very high concentration of these ions which attach themselves to air pollutants that are usually neutral so that they either have a negative or positive charge. Once charged, they become attracted to surfaces or other pollutants with the opposite charge. As they stick to each other, they become too heavy to remain airborne and settle on the floor or the walls to be cleaned or vacuumed later. Ionizers are very effective at removing common household air pollutants but often have trouble removing smoke, volatile organic compounds, and other odors. Another drawback is that ionizers tend to produce a small amount of ozone while they’re running. Ozone has been known to cause chest pain, coughing, and throat irritation even at low levels.

Electrostatic Precipitator/Electrostatic Air Cleaners

An electrostatic precipitator functions almost the same way as an air ionizer except that it has electrically charged plates that are able to collect air pollutants. For it to remain effective, these plates need to be cleaned regularly. If these collection plates are left to accumulate large amounts of particles, they may sometimes bond so tightly to the metal plates that vigorous washing and scrubbing may be needed to completely clean them. This is one of the downsides to owning an electrostatic air cleaner. Aside from that, it also produces small amounts of ozone and nitrogen oxide.

Ozone Generators

Ozone generators are popular — albeit very controversial — air purifiers that are used for cleaning the air. Ozone released by ozone generators have three oxygen atoms, one of which can remove itself and then reattach itself to pollutants. A chemical reaction then occurs to render these pollutants harmless. Unfortunately, studies have shown that the substances produced by the chemical reaction of ozone with pollutants can actually be more harmful than the pollutants themselves. In addition, several studies have already debunked the effectiveness of ozone generators. This is because, in order for ozone to effectively remove pollutants and kill bacteria and viruses, it has to release a higher concentration than the limitations set by the government. Furthermore, the use of ozone generators in small, closed spaces is dangerous since ozone in high concentrations can cause several health problems and trigger asthma attacks. Needless to say, it would be better to steer clear of ozone generators.

Thermodynamic Sterilization

Air purifiers that use thermodynamic sterilization (TSS) to clean the air are also rapidly gaining popularity as they require little maintenance, don’t make any noise, and don’t produce any harmful substances while in use. These models work by allowing polluted air to pass through the air purifier by the process of convection. The air passes through the air purifier’s ceramic core with micro capillaries which are heated up to 200°C. This process claims to incinerate 99% of bacteria, viruses, dust mites, mold, and fungus spores. It is important to know that air purifiers that use TSS do not actually remove or trap any airborne particles. Rather, they are rendered harmless due to the heat treatment. In addition, air purifiers that use TSS take longer to clean the air since no suction fans are used. However, one advantage of TSS in air purifiers is that they’re able to significantly reduce ozone levels in the environment.

Ultraviolet Germicidal Irradiation (UVGI)

Ultraviolet germicidal lights have long been used to eliminate microorganisms such as bacteria, viruses, molds, and fungi. They work by damaging the genetic material of these microorganisms, rendering them unable to reproduce and completely eliminating them in the process. This type of air purification technology is most commonly found in hospitals and laboratories where a sanitary environment is crucial. The main problem with UV light is that it is also harmful to plastics, human skin, and eyes, making it impossible to be used with people in the vicinity. Recent developments in air purifying technology, however, have allowed UVGI lights to be used in overhead ceiling lights in a manner that causes air near the ceiling to be irradiated. The systems are designed so very little of the UV light penetrates into the occupied portion of the room. Like with TSS technology, UVGI also does not target the removal particles. There are several factors that will affect the effectiveness of UVGI systems such as the intensity of the UV light, the duration of irradiation, humidity, the target organism, and other factors. Unlike ionizers and TSS air purifiers that require little to no maintenance, UVGI cleaners need their UV light bulbs replaced yearly which may be costly.

Photocatalytic Oxidation (PCO) Cleaners

Another emerging technology in air purification is photocatalytic oxidation (PCO). PCO cleaners also use UV light to react with a catalyst (usually titanium dioxide or TiO2). The reaction is able to oxidize bacteria, viruses, mold, fungi, odors, and volatile organic compounds. Oxidation breaks the pollutants down into harmless carbon dioxide and water molecules, making the air more purified. PCO cleaners are excellent at removing gaseous air pollutants like odors and VOCs. However, like TSS and UVGI, PCO cleaners are not designed to trap or remove particulate pollutants. Their UV light bulbs also need to be replaced yearly. In addition, PCO cleaners often have high commercial costs.

Whole House Air Purifiers

Whole house air purifiers, or central air purifiers, are designed to work in conjunction with your HVAC system and run continuously to purify the air throughout your entire home. They tend to be very effective and noticeably improve the air quality in your house. They require less maintenance, have longer-lasting filters, and don’t need separate power as they instead simply working off of your existing HVAC system. Whole house air purifiers vary in the way they are connected to your HVAC system.

Here are the three main types of whole house air purifiers depending on how they are installed:

  • Filter-based units – These are installed into your HVAC furnace systems and air intake points
  • Duct-based units – These are installed directly into the air duct path, either before or after the air handler in your HVAC system
  • Stand-alone units – These types of systems are installed in closets or attics, followed by installing additional air intake and exhaust into the home

Whole house air purifiers can cost thousands of dollars and would require an HVAC technician to have them installed. However, they’re ideal for those who aren’t keen on frequent cleaning and maintenance. Like air purifiers that use filters, whole house air purifiers also make use of filters to clean the air albeit at a much larger scale.

Some of the most commonly used whole house air filters include:

  1. Mechanical Filters
    Mechanical filters physically trap the particles in the air as they circulate through your system, holding them in the filter and preventing them from being introduced into your home environment. There are two types of mechanical filters: flat filters, which are commonly used in residential furnaces and air conditioners to protect the buildup of unwanted materials in the HVAC equipment, and pleated filters, which increase the efficiency of flat filters by layering them to make airborne particulates easier to trap and remove.
    Examples of mechanical filters include pre-filters, HEPA filters, and carbon filters.
  2. Electronic  Filters
    Electronic filters are very effective at removing very small particles and odors, but may be ineffective at removing larger particles. Therefore, they need to be used in conjunction with other filters to increase efficiency. Like with pleated filters, electronic filters also need to be professionally installed. The two main types of electronic filters include: electromagnetic filters, which use electrically charged wires to cause particles to gain a positive electrical charge which is then magnetically attracted to a collection plate, and ionic filters that give particles a negative charge and attract them to positively charged collectors.
  3. Ultraviolet Light
    Like room air purifiers, whole house air purifiers also make use of UV light to take care of biological pollutants such as bacteria, viruses, mold, fungi, and dust mites. Ultraviolet air cleaners are often installed as add-ons to an electrostatic system.
  4. Photocatalytic Oxidation
    Although not yet popular in the whole house air purifiers industry, some whole house air purifiers also make use of photocatalytic oxidation. With whole house air purifiers using this technology, it’s pretty much the same purification process: using UV light to react with a catalyst, different impurities oxidized and are rendered harmless. They’re excellent for removing a range of air pollutants including odors and VOCs. They’re virtually maintenance-free since there are no filters involved. However, the UV light bulb does need to be changed as needed.

Final Thoughts

As this article has shown, there are many options when considering an air purification system for your home. Whether you simply want to clean the air in a given room or want a more comprehensive solution integrated into your home’s HVAC system, this primer has hopefully provided a strong foundation for your ongoing search for the right model for your individual needs.

Further Reading