How to know if you need an air purifier (+ what it does and doesn’t do)

Exposure to air pollutants can lead to several adverse health effects. In low concentrations, air pollutants can lead to minor complaints, sleepiness, or a slight headache. Long-term exposure or exposure to high concentrations can lead to severe adverse health effects, including death.

Indoor air quality can be about 2 to 5 times worse than outdoor air, according to the US Environmental Protection Agency. Because of growing awareness of the importance of clean indoor air, air purifiers and air quality monitors are becoming more and more popular.

But how do you know if you really need to invest in an air purifier?

If you lack sufficient ventilation options or suffer from allergies or asthma, you need an air purifier that can provide additional help in cleaning the indoor air. The exact type of purifier that is required depends on the air pollutants that need to be addressed. An air purifier is a supplementary product to good ventilation and cleaning.

What does an air purifier do exactly?

An air purifier is a device that mechanically drives your indoor air through one or more filters. Hereby removing pollutants such as gases and airborne particles.

There are usually two types of filters. One that removes gaseous compounds, and one that removes tiny airborne particles. A good air purifier has both filters.

This does, however, not ensure that the air purifier can remove all pollutants present in the air. The removal of air pollutants depends on the type of filter and the removal efficiency of the filter.

What doesn’t it do?

An air purifier only removes particles (and gases) that are airborne. This means that particles that have settled on surfaces such as carpeting, bedding, or furniture are not eliminated. So, an air purifier does not ensure that you never need to vacuuming or clean again. It is mainly an addition to other good cleaning habits.

Keep in mind that a portable air purifier only cleans the room in which it is situated. On top of that, the capacity of the air purifier and the size of the room determine the effectiveness.

When do you need an air purifier

An air purifier is a supplementary product to improve your indoor air. Therefore, it is not a necessity unless:

  • you have allergies or asthma
  • you do not have the options to ventilate constantly
  • your ventilation is not adequate and you still have poor air quality despite ventilating
  • regularly cleaning the house and opening windows is not sufficient

Allergies and asthma

If you are highly sensitive to indoor air pollutants, have allergic reactions, or suffer from asthma, an air purifier can be a good investment. Allergies and asthma are both conditions that can be increased by the presence of airborne particles. Therefore, reducing the amount of airborne particles helps, according to several studies.

Insufficient ventilation

Ventilation is the single most important factor for good indoor air quality. So before you consider purchasing an air purifier, you should check whether you can improve your ventilation.

There are several ways to improve ventilation:

  • clean your ventilation system, vents and grilles regularly
  • replace ventilation filters often, approximately twice a year
  • improve indoor airflow by leaving your internal doors open
  • air out the house regularly by opening windows
  • install additional ventilation equipment

Even with good ventilation, there is the possibility that an air purifier is still effective. This is especially the case when the surrounding outdoor air is heavily polluted with for example smog (smoke + fog, mostly from heavy traffic or industry emissions).

Breathe clean air

When do you not need an air purifier?

You do not need an air purifier if you have an HVAC (Heating Ventilating and Air-Conditioning system) that is upgraded with additional air cleaning filters. If you clean and replace them often enough, you should be fine.

Cleaning your HVAC filters is recommended once every three months. On top of that, you should replace your filters twice a year. This of course depends on your personal situation. If you have pets or allergies, clean and replace them more often.

What type of air purifier do I need?

The type of filters, and therefore the type of air purifier you need, depends on the pollutants that are in your air. If you are not sure what type of pollutants are present in your indoor air, you can do some simple checks. There is no need for equipment. See my article: How to check the air quality in your home without measuring instruments (with infographic).

What do the different filters do?

There are many different filters for the many different types of air pollutants. The filters that are used in air purifiers are:

  • HEPA filters
  • MERV filters
  • Activated carbon
  • UVGI
  • Ionizer

HEPA filters

High-Efficiency Particulate Air (HEPA) is a standard that shows the efficiency of a filter. A HEPA filter removes dust, pollen, and pet dander from the air and is the best currently available filter on the market for particle removal. The required efficiency to be called HEPA is 99.95% in Europe and 99.97% in the US for particles 0.3 μm (one-millionth of a meter) in size. (source)

The efficiency of a HEPA filter in removing particles smaller and greater than 0.3 μm is higher than 99.97%. The mentioned efficiency is based on the particle size that is hardest to remove by the HEPA filter, which are particles the size of 0.3 μm.

A HEPA filter does not filter out gases and odors. Additionally, HEPA filters do not remove the very large particles such as settled dust. They cant filter these particles since they normally settle down quickly and therefore never reach the filter.

MERV filters

MERV or Minimum efficiency reporting value is a scale used to describe the efficiency of filters. The MERV scale shows the particle sizes that the filter can remove. This is mostly useful for determining if you really need a HEPA filter or not.

The MERV scale ranges from 1 to 16. From MERV 7 onward, they are about as good of a filter as a HEPA filter. MERV filters above MERV 16 are called HEPA filters. (source)

MERV rated filters do not filter out gases and odors. Additionally, similar to HEPA filters, MERV-rated filters cannot remove large particles as they settle too quickly and never reach the filter.

Activated carbon filters

Activated carbon filters are designed to remove gases from the air. They do this by binding the gases to the activated carbon, making them solid instead of gaseous. This happens through a mechanism called adsorption, which makes the tiny gas and odor particles stick to its surface.

Activated carbon does not remove particles from the air.

UVGI filters

Ultraviolet germicidal irradiation or UVGI is used to kill microorganisms such as bacteria and molds that pass along UV light. These microorganisms are hereby rendered harmless. Unfortunately, these microorganisms often survive UVGI as the exposure time is generally too short.


An ionizer emits small negatively charged particles (ions) into the air. These ions attach themselves to airborne particles. Hereby, the particles get charged and are attracted to other particles. Because of this, they become heavier and settle faster, and cling to surfaces in your room like walls, furniture, or the filters of your air purifier.

Ionizers are known to be able to release ozone, a harmful gas. Because of this the EPA does not recommend using ionizers. However, the ionizers that are part of some air purifiers are thoroughly tested and comply to standards limiting ozone emittance. Additionally, some air purifiers come with the option of turning off the ionizer. In this way, you can for example only turn on the ionizer when you are not in close proximity to the air purifier.

Overview table of filters

The following table shows what type of filter removes what type of air pollutants. Additionally, some limitations to the filters are mentioned.

Table 1. Filters, removed pollutants, and limitations (source)

Type of filterAir pollutants removedLimitations of the filter
HEPAAirborne particlesDoes not remove larger particles. Does not remove gases and odors
MERVAirborne particlesDoes not remove larger particles. Does not remove gases and odors
Activated carbonGasesNeeds to be replaced often (twice a year)
UVGIMicroorganisms such as bacteria and moldEffectiveness can be low since the exposure time is limited
IonizerAirborne particlesIt is unclear how well they work since an ionizer does not filter air. Additionally, ionizers release some amount of harmful ozone gas

The importance of the Clean Air Delivery rate

An air purifier can only clean so much air at a time. Therefore, the size of the room determines the required caliber of an air purifier. The caliber of an air purifier is the Clean Air Delivery Rate (CADR). This is the amount of air in cubic feet per minute that is cleaned by the air purifier. However, the CADR only applies to the removal of particles, not to the removal of gases.

The minimum CADR is dependent on the room area. The table below shows the CADR needed for several room sizes in square feet (1 square foot is about 0.1 square meter).

Table 2. Estimated minimal CADR requirements (source: EPA)

Room area in square feet100200300400500600
minimum CADR65130195260325390

Keep in mind that this table’s calculations are based on a height of 8 feet (2.5 meters). If you have a higher ceiling, you will need an air purifier with a larger CADR.

Additionally, the CADR rating is based on a test-run of 20 minutes. When an air purifier runs for some time, the filter will get full and the CADR decreases. Therefore, make sure that you select an air purifier that has a higher CADR than necessary for the size of your room.

Multiple CADR numbers per air purifier

Normally, there should be three CADR numbers listed on an air purifier. These are for the different contaminants, smoke, pollen, and dust. Smoke has the largest particle size (and is therefore visible), pollen are smaller, and dust has the smallest particles.

Smaller particles are more dangerous since they can penetrate the lungs more easily.

What are the most common indoor air pollutants?

The most common indoor air pollutants are:

  • VOCs
  • formaldehyde
  • fine dust
  • mold
  • carbon monoxide
  • CO2
  • radon

You can read all about these air pollutants, their health effects, and what you can do about them in my article: The complete indoor air quality guide for your home (with giant overview table).

Room full of plants

The disadvantages of an air purifier

There are a few things you might want to consider before purchasing an air purifier. These are:

  • noise
  • initial investment
  • operating costs (electricity), and
  • filter replacement costs
  • potential ozone producton

Some air purifiers produce small amounts of ozone, normally far below dangerous levels. However, you should avoid ozone generators as they produce larger amounts of ozone, which is a lung irritant.

You can read all about the disadvantages of air purifiers in my article: What are the disadvantages of an air purifier?

Which air purifier do I recommend?

There are many air purifiers available on the market. I looked at many different air purifiers and landed on the Coway Mighty. This is an affordable and quiet air purifier that lets you know when to replace its filters. On top of that, it has almost 4000 reviews on, of which 77% gave the maximum of 5 stars rating.

The Coway Mighty has four filters. A pre-filter to capture large particles, a deodorization filter, a HEPA filter, and a vital Ion (ionizer). The CADR is as follows. Dust: 246, pollen: 240, smoke 233.

The Coway Mighty, fit for rooms up to 361 square feet (33.5 square meters)

Check out the Coway Mighty on

What about houseplants?

There seem to be many blog posts on the internet claiming that NASA published a list of the best houseplants to purify your indoor air.

The truth, however, is that proper ventilation is by far the most important for indoor air quality. Plants should never be a substitute for good habits such as ventilation and regular cleaning. I wrote an entire article on the topic of houseplants and air quality, which you can read here.

What about an air quality monitor?

Personally, I am a fan of air quality monitors over air purifiers. Air quality monitors do not remove any compounds from the air. However, they detect them and can trigger you to clean more often or air out the house. In addition, air quality monitors do not make any noise.

On top of that, the air quality monitor lets you know exactly what you are dealing with. For example, an air purifier does not remove CO2 from the air. I would want to know my indoor CO2 levels and open a window if it is too high.

Also, the US Environmental Protection Agency (EPA) states: ‘EPA does not recommend using air cleaners to reduce the health risks associated with radon’. This is mostly the case because radon requires more drastic measures as well as source control. (source: EPA) You can read all about radon in my article: What is radon?

So, if you are concerned about radon, an air quality monitor that shows your levels of radon might be a better investment.

Why I recommend using an air quality monitor instead

Although an air purifier is a wonderful tool, ventilation is still your best weapon against indoor air pollution. Therefore, measuring the air with a good air quality monitor and ventilating when necessary is an excellent alternative to an air purifier. An air quality monitor has the advantage over an air purifier in that it tests for more compounds than an air purifier can remove. For example, an air quality monitor informs you about the presence of carbon monoxide and radon. An air purifier does not, and can’t remove these compounds from the air.

In looking for the best air quality monitors available, I found a Norwegian company called Airthings, which produces exceptional air quality monitors. They are easy to operate (just wave your hand in front of the device) and send their data to an app on your phone.

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