How Does an Air Purifier Work? All You Need to Know

How Does an Air Purifier Work? All You Need to Know

Want to know how an air purifier works before buying one? It’s pretty simple how it functions. Just look at this simple diagram:

dirty air plus air purifier equals clean air

An air purifier manufacturer can combine one or more filter types to clean and sanitize indoor air. But, the most basic idea in air purification systems is on the diagram we just showed you.

Basically, an air purifier draws in the dirty indoor air, cleans it through multiple stages of filters and delivers it out clean and filtered.

It works as an air cleaning machine that rids the air from suspended particles, dusts, smoke, fumes, pollens, pet danders, hair and even germs and biological contaminants.

Of course there’s more to it than this basic explanation. If you want to know how it really works from the inside out, read on! We will answer the most frequently asked questions about how most air cleaners function.

Table of Contents:

  • How an Air Purifier Cleans the Air
  • How Does an Air Filter Work?
    1. True HEPA filter
    2. Activated Carbon Filter
    3. Ionizer
  • Does it Work like a Humidifier?
  • How long Does an Air Purifier Take to Work
  • Does an Air Purifier Work Like a Fan
  • How to Improve Your Indoor Air Quality
    1. Room Area to CADR
    2. ACH and CADR

How an Air Purifier Cleans the Air

There are two main ways how air purifiers work – either through negative ionization or by mechanical filtration.

  • Mechanical Air Filtration – this uses a HEPA filter, activated carbon filter and some models even integrate a UV-C filter to clean the air
  • Negative Ionization Generators – use charged wires to create negative ions to pair with ions found in dirty air, weighing them down to stick with the nearest object.

Different air purifier brands have a variety of procedures of cleaning the air. The most competitive designs use multi-stage air filtering processes.

Filters are usually subject to replacement every 3 to 4 months, depending on the machine manual. This is to let them perform optimally and make sure it really cleans your indoor air without recirculating the contaminants.

How Does an Air Filter Work?

how air filter work with true hepa filter, uvc light, activated carbon and pre filter

Air filters work by trapping pollutants, dusts and pollens and germs. Certain filters such as carbon filters trap odors, fumes and VOCs (volatile organic compounds).

Commercial air purifiers used in the households, studio apartments and offices are usually equipped with a HEPA filter and activated carbon.

There are also ionizer air purifiers which give off ions to pair up with ions found in suspended particles in order to clean the air.

Below are some of the most common air filters and how they work.

1. True HEPA filter

true hepa filter that captures submicron particles down to 0.3 microns at 99.97 percent
Image Credit: Whirlpool (True HEPA Filter)

True HEPA filters can capture submicron particles down to 0.3 microns with at least 99.97% efficiency (ASME).

To help you visualize this, the tiniest particles visible to the naked eye is about 10 microns. Anything smaller than this cannot be seen.

HEPA stands for High Efficiency Particulate Arresting. It is designed to satisfy the requirements set by the ASME or European standards.

Particles captured by a True HEPA filter include the tiniest dust particles, pollutants and pollens which can get into the lungs. They can also capture viruses and bacteria, such as Aspergillus niger, Penicillium citrinum, and nanoparticles, such as the Coronavirus .

2. Activated Carbon Filter

Activated carbon, composed of powdered, granular blocks of carbon, has an absorbent property. This enables it to soak up contaminants and allergens through its charcoal bed filter.

Activated carbon filter is a popular filtration component for gases, volatile organic compounds (VOCs) and chemicals. The only downside is that the carbon filter is not highly efficient in removing dust particles, mites, hairs and pollens.

Hence, high performance air purifiers are often integrated with a HEPA filter and activated carbon filter to filter both particles and fumes.

true hepa filter that captures submicron particles down to 0.3 microns at 99.97 percent

How do Activated Carbon Filters Work?

Filthy air will enter the purification system passing through the activated carbon. It leaves the filter layer purified. When used with a HEPA filter, the carbon layer prevents bigger particles from reaching the HEPA.

3. Ionizer

Ionizers use electric charges to clean contaminated air. It is capable of reducing the size of contaminants to 0.1 microns, which can often be seen as more precise than True HEPA filters.
However, ozone emissions can be dangerous to your health, especially if it is more than 0.05 parts per million (ppm).

Hence, true HEPA air purifiers with UV light filters are usually better preferred than ionizer air purifiers. Some brands such as the Blueair, combine ionizer filters with HEPA technology which creates an effective air cleaner.

Another upside of ionizer filters is that you won’t have to replace it every now and then unlike HEPA filters.

How Ionizer Filter Works?

The ionizer works by using electricity to give off negative ions in your indoor environment to charge air with airborne contaminants. Upon charging particles with static, they simply drop down to your furniture or stick onto the nearest object. This way, it rids the air from contaminants and you’ll feel the fresh, filtered air.

4. UV-C light filter

The UV-C light filter is a type of filter that’s used in high performance air purifiers that is capable of killing viruses and bacteria. Integrating this with a True HEPA filter and activated carbon, this can be a powerful air cleaning machine.

For example, the HA-HL15 Air Disinfection Purifier has 5 types of filters for sanitizing the air. One of these filters is a UV-C light filter. It also has a HEPA filter and activated carbon and thereby designed for facilities to trap contaminants, rid bad odors and kill viruses.

How Does a UV Filter Work?

In air disinfection purifiers, the UV-C light filter has a wavelength of 256 nm that deactivates microbial activities. As the True HEPA filter and activated carbon trap these pollens and viruses, the UV filter destroys these microorganisms and prevents further reproduction. Thus it not only cleans indoor air, but also sanitizes it.

Some Misconceptions about How Air Purifiers Work

Does it Work Like a Humidifier?

does an air purifier work like a humidifier - a common misconception that they are the same

Air purifiers do not work like humidifiers as the latter do not add moisture to the air. The humidifier dispenses “smoke-like” mist into the air to increase its moisture content, but it doesn’t clean the air. Air purifiers clean the air but it doesn’t make the air humid.

Does an air purifier work like a fan?

No, an air purifier doesn’t work like a fan. By design, it supposedly does not cool the room. However, some air purifiers having high air flow rates can blow more air in the environment.

To know if your air purifier choice can blow out more air, check the CADR rating. CADR is short for Clean Air Delivery Rate, which tells you how strong the machine can dissipate the air in a specific room size in CFM.

As an example, the Dyson Pure Cool Link, Dyson Pure Cool Tower and Dyson Pure Hot+Cool are designed with high fan power to cool the room while cleaning the air.

how Pure Cool Link High Power Fan works as an air purifier with a fan cooler

Conventional air purifiers are designed to operate in a more quiet manner , but with a high fan power, these Dyson air purifiers operate louder than the others.

How Long Does an Air Purifier Take to Work?

By virtue, an air purifier may take 15 minutes to an hour to clean the entire air volume in the room. But this measurement is based on the circumstances that all windows and door openings are closed or blocked.

In reality, the safe estimate for an air purifier to clean a room is about 45 minutes to 3 hours. Factors include the power setting, CADR and ACH of the air purifier.

Does an Air Purifier Work with Open Windows

An air purifier works by taking in the volume of dirty air in a room and cleaning it. So naturally, it works best if all windows and doors are closed.

However, even if all windows are open, the air purifier can still significantly lower the contaminants in a room.

A study by the shows that pollution levels are reduced by 60% in 20 minutes even when all windows are open . Comparatively, a room with closed windows can reduce contaminants at 90%.

graph showing how window open and window closed affects air purifier performance

So yes, air purifiers can still significantly work even if all windows are open.

How to Improve Your Indoor Air Quality

In order for the air purifier to work at its best efficiency, you must select a product that should cover your room area and filtration requirements.

Choose a machine that can deliver:

  • the CADR required for your room area
  • the number of times the air should be exchanged (ACH) based on the type of room you have (hospital, isolation room, living room or bedroom).

Room Area to CADR

So how can you use the CADR to choose the best air purifier that works suitably for your room?

The simplest way is to consider the AHAM’s ( Association of Home Appliance Manufacturers ) recommendation. Simply get your room size in square feet and divide this by 1.55. This formula is valid for rooms with ceiling height of 8 ft.

For example, your bedroom is 150 sq. ft. To get the CADR, divide 150 by 1.55 and you’ll get 96.77. This means you need to get an air purifier with a CADR of 97 CFM or higher to work efficiently for your room size.


The Air Changes per Hour is based on the type of room and application you have. The more critical the activities in that space, the higher the air exchanges per hour should be.

All spaces in general should ideally have an ACH of 4 or higher. This means the air purifier should clean the air in your room 4 times in an hour.

Say you want an air purifier in your bedroom. The suitable ACH for this is 4. In reference to the example above of 150 sq. ft. bedroom, multiply the CADR by the required ACH. That’s 97 CFM times 4 ACH equals 387 CFM.

This means, in order for your air purifier to work in its most comfortable/suitable way, choose one with a CADR of 387 CFM (or 400CFM) based on 4 ACH.

We can summarize this by the following formula to get the most suitable air purifier to work for your space:

CADR needed = [Room size (sq. ft) / 1.55] x ACH

Air Purifiers for Different Room Types Recommended Air Purifiers for different pollutants Coverage CADR Useful Guide
Hospitals HisoAir Model HA-1601(Medical grade air purifiers) 55-94 square meters 800 m3/h mold spores in the air
Commercial Areas HisoAir Model HA-1300(air purifers for 1500 sq ft) 90-180 square meters 1500 m3/h musty smell in basement
Car & Garbage HisoAir Model HA-139(Air purifiers for 300 sq ft) 28-48 square meters 400 m3/h radon
smoke smell
Office & Work Space HisoAir Model HA-W400(Air purifers for 400 sq ft) 30-50 square meters 444 m3/h Dust floating in the air
Hair Salon
Nail salon
HisoAir Model HA-139 28-48 square meters 400 m3/h seasonal allergies
Home & Kitchen HisoAir Model HA-1601 (Air purifiers for mold) 55-94 square meters 800 m3/h Formaldehyde
Cooking smell in the kitchen
Air purifier for hotel Room HisoAir Model HA-1968 (Air purifiers for 2000 sq ft) 90-180 square meters 1500 m3/h Dust
air purifier chool & Classroom HisoAir Model HA-1968 (Air purifiers for smoke) 90-180 square meters 1500 m3/h weed smell
Air purifier for living Room HisoAir Model HA-139 28-48 square meters 400 m3/h Pet odors
cat allergies naturally

You can use this table to determine the appropriate size of air purifier for your occasions.

Wrapping Up

Knowing how an air purifier works is important in choosing the best air purifer brand/features for your living space or industry. More useful than a Himalayan salt lamp, an air purifier works by cleaning your indoor air and improving air quality. We’ve discussed different types of filters in air purifiers. Some air filters are for trapping contaminants, others for odors and still others for killing viruses.

We’ve also answered some misconceptions about how air purifiers work. Lastly, we added a tip on how you can choose an air purifier that works best in your space requirements.

HisoAir is an air purifier manufacturer in China with over 15 years experience in the production of air purifiers. For business inquiries or to request a quotation, please contact us through our contact form .

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