Are air purifiers good for COVID-19?

This article discusses the efficiency of air purifiers against SARS-CoV-2, the virus responsible for causing the novel coronavirus. 

Are air purifiers good for Covid 19?

Yes, air purifiers can be effective against the spread of covid-19 in an indoor environment. However, air purifiers are not a foolproof solution against the coronavirus.

How covid-19 spreads 

Since the onset of 2020, the novel coronavirus has wreaked havoc in all parts of the world, forcing a global pandemic. The disease affects the respiratory system, and can even cause death.

The novel coronavirus spreads mainly through aerosols and droplets, but cannot spread on its own as an airborne virus. There are a few ways people can come in contact with the virus, which include:

1. Direct or indirect contact: 

The virus can be transferred by contacting an infected person’s mouth, nose, or eyes after touching an infected object or surface. 

For this type of transmission, air purifiers are ineffective. For this type of transmission, good hygiene, which is a sort of source control, is beneficial.

2. Droplet spray in short range transmission:

When an infected individual exhales, the virus can spread through respiratory droplets (breathes, coughs, sneezes, sings, yells, or talks). 

These droplets are often bigger (>5 microns in diameter) and fall out of the air in seconds to minutes. For this type of transmission, air purifiers are ineffective. 

This type of transmission may be prevented through social distance and masks, as well as tailored filtration pressure differentials.

3. Aerosol in long-range transmission (airborne transmission):

When an infected individual exhales, little respiratory droplets (less than 5 microns in diameter) are produced. Smaller, aerosolized viruses can linger in the air for a long time and move long distances on air currents. 

For this type of transmission, air purifiers and customised filtration pressure differentials might be beneficial.

What is an air purifier and why do we need it?

Air purifiers are devices which, as the name suggests, clean the ambient air. There are mainly two types of air purifiers, namely:

  • High efficiency particulate air (HEPA) filters
  • Air ionisers

These air purifiers can have additional components, such as a UV light chamber, activated charcoal filter, and so on, which are mainly designed for widening the spectrum of the device’s efficacy against various pollutants.

Many people wonder whether an air purifier is the right investment. However, in the current scenario, where air pollution is prevalent and worsening with each passing day, especially in urban areas, air purifiers are very vital.

Air pollution is the presence of undesired substances in the form of solids, liquids, or gases, which are suspended in the ambient air, and can adversely affect human health.

These pollutants can be especially harmful if present in the indoor environment. The average human being spends more than 90% of their total lives in an indoor environment, with more than 80% of it inside a building.

Indoor air, just like outdoor air, is susceptible to pollution. Indoor air can get polluted when pollution from outdoors infiltrates through openings such as doors, windows, cracks, seeps, etc.

Indoor air can also get polluted from indoor sources, which can arise from things such as furniture, household items, solvents and dyes, spores from mold and mildew, combustion of fuels and firewood, and hobbies/activities such as smoking, etc.

The pollutants generated from these sources have been shown to adversely affect human health, and continuous exposure to elevated concentrations can cause many serious issues, such as cancers, respiratory and cardiovascular disorders, and even death.

This is where air purifiers come in. They help to get rid of the pollutants in the indoor air, thereby keeping it clean and fit to breathe.

How HEPA air filters help

Air purifiers with a HEPA filter simply pull in air from the indoor air, pass it through the filter, and release the purified air back in the enclosure.

The HEPA filters are very popular nowadays, as they have an efficiency greater than 99% against particles that are equal to or greater than 0.3 microns in diameter.

The viral coronavirus cells cannot stay suspended on their own in the ambient indoor air. They require a surface, such as a particle, mucus, droplets, and so on, in order to be transmitted from one place to another.

Most of the times the particles that act as a medium for SARS-CoV-2 viruses have an aerodynamic diameter which falls above the cutoff limit for HEPA filters.

Some filters also utilise the method of electrostatic precipitation, in which a filter surface is charged. This helps to ensure that once a particle is trapped, it stays trapped and thereby does not get re-circulated in the indoor air.

However, it is important to know that the efficiency of an air filter depends upon the overload, which refers to the amount of dust or other undesirable particles that have been entrapped in the filter.

The efficiency of an air filter can drop significantly as the load increases. This implies that if you are using an air purifying device which has old filters, you may still be at a relatively higher risk of being infected with respect to when you use a new filter.

Another thing that is important to note is that the filters themselves cannot kill the viruses; they merely entrap the particles which may contain the virus. 

Therefore, it is important to make sure that once the filter is being disposed of, you are taking the proper precautions in order to keep yourselves as well as the people around you safe from COVID-19.

What is the ideal location of placing an air purifier to ensure minimal risk of COVID-19

One must be careful when it comes to choosing a spot for placing an air purifier. This is because in certain conditions, the optimal functioning of the air filter can be impeded.

Place it near sources of pollution

Certain areas in the house are prone to be sources of air pollution.

For example, if a room in your house has a mold problem, or a room where smoking and other combustion-related activities occur, there is particulate matter present in that area. 

Therefore, keeping your air purifier near the source of pollution would be an ideal scenario, as it would also prevent the spread of those pollutants to other rooms in the house.

Place it in rooms with a high air exchange rate

Air exchange rate refers to the amount of air that passes through a certain area from its surroundings.

For example, a living room can be considered an area of high air exchange rate, as it is connected to other rooms as well as the outdoor environment.

Placing the air purifier in such regions would be ideal, as these rooms also receive the highest amount of air pollutants, and can potentially transmit them to other rooms as well.

Do not place it in a corner

In a typical household setting, the air seldom goes to the corners. This implies that air pollutants present in the indoor air would be sparse in corner areas when compared to the central areas. Therefore, you should avoid placing it in a corner.

Place it at least 3-5 feet above the ground

When air gets heated up, it becomes light and rises up, causing cold air to descend. In the process, the air pollutants get entrapped and get lifted off the ground.

So, mounting the air purifier on the wall would be ideal, as not only would the air purifier capture the pollutants in the horizontal air flow, it would also filter out the particulate matter which is present in the vertical air flow.

Place it in your bedroom

A person is at their most vulnerable while they are sleeping, especially when it comes to infections, since the body is repairing the wear and tear one experienced throughout the day.

Under such circumstances, it is not ideal to sleep in a polluted bedroom. Doing so can not only cause respiratory problems such as wheezing, coughing, irritation in the nose and throat, but can also make you susceptible to COVID-19.

Ideally, you would want to place the air purifier at least 5-6 feet away from your bed, so that it doesn’t blow the air directly on your face. Furthermore, this is very helpful in seasons such as summers, when hay fever is prevalent.

Place it in rooms which have the highest occupancy of people

Rooms where a lot of people are present usually are the ideal spot to place the air purifier. Especially if some people in the room have pre-existing respiratory health issues.

Not only would this help to reduce the chances of coming in contact with the coronavirus, but can also help vulnerable people to breathe more easily.

Other FAQs about Air Purifiers and Filters that you may be interested in.

Can you run an air purifier and humidifier at the same time?

Can air purifiers help with mold?

Should I turn on the ionizer on My air purifier?


Air filters can help to keep in check the spread of covid-19 in an indoor environment. However, the filters themselves cannot kill the virus.

However, these devices can only stop the viruses that are spreading through long-range transmission via aerosols such as droplets, particles, etc.

For contact-based and short range transmission, it would be ideal to ensure safety protocols are followed, since air purifiers are ineffective against them.

Lastly, placement of the filter is key. The best suited place for installing your air purifier is on the wall, at a height of about three to five feet above the ground, in a room which receives the highest airflow rate with respect to the other rooms.

Furthermore, care should be taken when placing the air purifier. It is necessary to ensure that there is no obstacle in its path, and it is away from other electronic devices at least by a distance of 5 feet.

However, due to certain circumstances, it would not be ideal to mount the air purifier unit on the wall. However, there are many models available in the market which are designed based on the user’s preference to place the air purifier.

Lastly, it is important to buy an air purifier which has a coverage area suited to the requirements of the user.


In what conditions does the COVID-19 virus survive the longest?

COVID-19 viruses thrive the most under conditions where there’s low light, low relative humidity (i.e., <50%), and temperatures at or below room temperature.

Therefore, it is important to maintain temperature and humidity levels within your house, especially in rooms which do not receive an adequate amount of sunlight.

How often should I replace my air filters?

The frequency of replacing your air filters depends upon the indoor air quality of your house. If you live with a small number of people, have pets, and are near a polluted area, you might need to replace your filters as early as 1-2 months.

However, if you live alone with no pets or other animals, you can replace your filter once every 6-12 months.


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