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How Do Air Purifiers Work?

Last updated March 2, 2023

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Author avatar Paul Allen

Paul is our go-to-guy for air purifier and dehumidifier reviews. His apartment has become a de facto HouseFresh test lab where he pits the latest clean air technology against the perils of city center life. When he’s not putting a purifier through its paces, Paul likes to endlessly dig through dusty record shops (making his dust-free apartment even more important).

A simple search for an air purifier can lead to endless hours of reading, full of technical jargon, elusive statistics, and in some cases, false promises. To cut through the noise, we’ve decided to debunk and demystify how an air purifier works and what it can actually do. Leaving you to feel confident making an informed decision, knowing what to look out for (and what to avoid) when buying a purifier. 

But you may still be wondering, why should I buy an air purifier in the first place? 

In a world of increasing wildfires, pollution, and deadly viruses and bacteria, never has it been as important to pay attention to the air you breathe. By using an air purifier in your home, you can target a range of harmful pollutants such as:

🌼 Biological sources such as mold or pollen

🚬 Combustible sources such as wildfire or cigarette smoke

🐕 Household sources such as dust or pet dander

🚗 External sources such as industrial or traffic pollution

💅🏽 VOCs such as chemical fumes or odors

What many people don’t realize is that indoor air is found to have 2 to 5 times higher concentrations of pollutants than what you’d typically find outdoors. 

As the average American spends 90% of their time indoors, that equates to a lot of time spent exposed to harmful pollutants, unless you take precautions to cleanse the air

What Does an Air Purifier Do?

Removing harmful pollutants from the air sounds great in practice, but how does an air purifier go about it?

When you boil it down to its simplest form, an air purifier is essentially a fan that draws vast amounts of air into the unit, where a range of filters capture any airborne particles. Leaving clean air to be redistributed into your space.

In essence, therefore, the more powerful the fan and the more efficient the filters that the purifier possesses, the more effective the unit will be at cleaning the air. Allowing you to breathe easy in the knowledge that the wide range of pollutants that exist in your space have been eradicated. 

How Do Air Purifiers Work?

While we can reel off the benefits of air purifiers for hours, we understand seeing is believing. So, let’s delve deeper into what is inside an air purifier and explain how they bring about such benefits. 

It’s important to remember that not all air purifiers work in the same way. Some will use simple mechanical filters while others rely on different technology such as UV-C or ionizers. Air purifiers can also be set up to target different pollutants based on the filters they use, although using a combination will allow you to remove a range of particles such as dust, odors, pet dander, smoke, or even viruses and bacteria.  

The key components of a good air purifier include a three-stage filtration system of pre-, carbon, and HEPA filters along with a powerful fan to boot.

So, let’s dive into what each of these parts bring to the table. 

1. The Pre-Filter 

The first line of defense within many air purifiers is the pre-filter. As air enters the unit, you can expect to find a whole host of polluting particles that remain suspended in the air. The pre-filter’s job is to capture any of the larger particles on entry such as:

  • Hair
  • Dust
  • Cloth fibers

The pre-filter can be made up of different materials, such as a fine plastic mesh, a metal grill, or material web. You’ll find this is usually a long-lasting or permanent filter that can be cleaned in between use. While some can be removed to be cleaned using hot soapy water, others simply remain installed inside the unit and can be cleaned with a brush or vacuum cleaner.

By capturing larger particles, the pre-filter will improve the performance of your HEPA filters, prolonging their lifespan and allowing them to work on the finer particles found in your space.

2. The Carbon Filter

Next, you’ll find a carbon filter inside most purifiers. This filter works to eradicate Volatile Organic Compounds (VOCs) from your environment. But what on earth is a VOC I hear you ask? Well, this term covers a wide range of different gaseous pollutants, from chemical fumes to everyday odors.

These pollutants emerge from obvious sources such as cleaning supplies and cooking smells to obscure sources you may not even realize are affecting your air quality, such as the chemical coatings on your furnishings and carpets that seep into the air over time.

Of course, breathing such pollutants is not great for your health and has been found to contribute to a range of health conditions such as irritation of the eyes, nose, and throat to more serious conditions such as damaging the central nervous system and other organs. 

So how does a carbon filter work to remove odors and gasses from the air? It all comes down to the porous nature of carbon. Within the carbon filter, you will usually find millions of small charcoal beads or pellets that form a tightly packed layer. As the air passes through this filter, VOCs are adsorbed by the carbon, which locks them in the filter whilst neutralizing their potency.

3. The HEPA Filter 

The last, but by no means least, filter we will look at is the HEPA filter. This is a key stage of purification and arguably the filter that will transform your air quality the most. 

Made up of tightly-woven fiberglass strands, structured inside densely packed pleats, HEPA filters create a maze for particles to pass through. The denseness, along with the sticky nature of the fibers, makes them incredibly efficient at removing pollutants. 

In fact, the term HEPA is a stamp of approval, certifying that this filter can capture at least 99.7% of airborne particles as small as 0.3 microns. 

This makes them extremely effective at targeting ultrafine particulate matter, such as dust, dander, mold, and even microscopic bacteria and viruses. This helps to alleviate allergies and remove harmful toxins that can seriously affect our health if inhaled.

In order to be granted HEPA certification, the filter must be independently tested by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE). During the tests, the filters are put through their paces and rated by their Minimum Efficiency Reporting Values, or MERVs, measuring their efficiency at capturing varying-sized particles, all the way down to ultrafine size.

While the HEPA certification guarantees that a filter can remove at least 99.7% of any airborne particles, there are 3 different levels of HEPA filter with increasing levels of efficiency. ‘HEPA type’ filters offer the benchmark through to ‘Medical Grade HEPA’ filters which offer unrivaled efficiency, capturing 99.99% of particles as small as 0.1 microns. 

4. The Fan 

Now you may be wondering how these filters actually come to catch polluting particles. This is down to the fans inside of the unit. 

The purifier’s fan works in two ways, to draw dirty air into the unit and to expel clean air back into the home. Although this may seem secondary to the purification process, the fan itself plays a huge role in cleaning the air in your home. After all, without effective airflow, the filters would not be able to purify much air at all.

With this in mind, it’s important to consider how powerful the fan is. A purifier with a powerful fan will be able to circulate far more air than one with a lower-powered fan, thus offering the user more air changes and enhanced cleaning capability.   

In order to determine the power of a purifier’s fan, check out the unit’s CADR rating. This is an independent score that measures how efficiently a purifier can clean a space, given in CFM (cubic feet per minute), which will indicate the unit’s airflow.

The Different Types of Air Purifier Technology

Technology #1: Mechanical filter

Mechanical filters are another term for filters that capture particles as air passes through the purifier, such as a HEPA filter or bed of activated carbon. An example of this type of air purifier is the Levoit Core 600S.

Do mechanical filter air purifiers work? This technology is arguably the most effective. Mechanical filters will be found in the vast majority of air purifiers on the market and are certified to remove particles from your space. Our study of the best air purifiers for virus and bacteria list has some of the very best mechanical filters available currently.

Technology #2: Ionizer

An ionizing purifier works by electrostatically charging airborne particles, adding negative ions to the pollutant. This can come as a standalone device, however, it is usually paired with a mechanical filter. Check out the Coway Airmega AP-1512HH for a good example.

Do inoizer air purifiers work? The negative ions make particles ‘sticky’, meaning they are easier for the purifier to capture. This technology, however, is often attributed to releasing potentially harmful ozone into the atmosphere, so ensure you look for an ozone-free ionizer. Many of the Coway and Blueair contain ionizers but they provide extremely low levels of ozone to humans and can clean more for less $ invested.

Technology #3: UV-C

These purifiers (like the Leitz TruSens Z-3000) utilize UV light to sterilize harmful pollutants as they pass through the unit. Again, these usually come alongside other filters to double up protection.

Do UV-C air purifiers work? UV lights are very effective at killing harmful bacteria and viruses when exposed in this way. The UV bulb, however, will not work to capture any other airborne particles so should be used in conjunction with a HEPA filter and even when they are used – the jury is still out on their effectiveness. You are better of with a HEPA and activated charcoal filter every time.

Technology #4: Filterless

Certain purifiers are able to eradicate pollutants without the need for a filter. Instead, these units use thermodynamic (TSS) or UV light to neutralize harmful pollutants.The AIRFREE P1000 Filterless Air Purifier is a good example.

Do filterless air purifiers work? Nope in most cases, they just move air around the room but the science behind HEPA means that filters need to be replaced otherwise they are not effective at removing pollutants from the air. Pay a bit more and expect that you will need to keep paying for filters but look at low-cost replacements like the Smart Health S.

The Air Purifier Jargon Buster 

Still confused? Use our jargon buster as a quick guide to refer to when buying an air purifier.

Jargon What Does It Mean?
HEPA filter🤓 Stands for: High Efficiency Particulate Air [filter]. 
The term HEPA is a certification that a filter can theoretically remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns (µm). 
It’s basically a mega filter that removes problematic particles that you can’t even see. All the best air purifiers have one. 
CADR🤓 Stands for: Clean Air Delivery Rate. 
Most Air Purifiers come with a CADR score, which is calculated by measuring the volume of clean air that is produced when it is used against the three most common pollutants: dust, pollen, and smoke.
Basically, the higher the score the greater the efficiency.
VOC🤓 Stands for: Volatile Organic Compound. 
This term covers the gasses an air purifier can capture. From chemical fumes to odors. 
ACH🤓 Stands for: Air Changes per Hour. 
This indicates how many times a purifier can completely cycle the air in a given space every hour. 
PM 1 / 2.5 / 10🤓 Stands for: Particulate Matter. 
With the number indicating the size of particles in microns. PM 1 is also known as ultrafine particulate matter, likewise PM 2.5 is known as fine particulate matter.
Micron🤓 One micron is equal to one millionth of a meter (0.001mm). 
This is the unit of length used to measure airborne particles and determine how effective HEPA filters are. 
Adsorption🤓 Often mistaken for absorption, adsorption refers to a substance’s ability to attract and adhere to atoms or molecules of gasses or liquids. 
In this instance, it is used to describe how VOCs and odors are captured by carbon filters. 
Ozone🤓 Ozone is a highly reactive gas composed of three oxygen atoms. 
Although this is produced naturally in the earth’s atmosphere, it is also a man-made pollutant that is harmful to humans. Ozone is often produced as a by-product of some purifying technologies such as Ionizers and UV bulbs. 

Final Thoughts 

Being able to separate the wheat from the chaff and find a purifier that will actually make a difference to the air you breathe is no easy task. 

By knowing exactly what a purifier does, the key components that make it effective and understanding the jargon often used to mystify buyers, we hope you feel confident to find the perfect purifier so you can begin to transform the air in your home.