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Find out how ventilation helps you lower the spread of COVID-19.

Why ventilation is important

Ventilation means bringing fresh outdoor air into an indoor space. Ventilation is important because COVID-19 is airborne.

COVID-19 spreads when a person breathes out very small droplets or aerosols that contain the virus. Aerosols can float in the air for a long time and other people breathe them in, spreading the virus.

Adding fresh air into a space reduces the number of aerosols in a room and reduces the risk of COVID-19 transmission from one person to another.

Good ventilation, along with other simple steps such as face masks and testing, reduces the risk of spreading COVID-19.

How to choose well-ventilated spaces

Choose to meet or sit outdoors whenever you can. In most cases, outdoor settings have better natural airflow than indoor areas.

Check for good ventilation when you're indoors

The more visible signs of ventilation, the lower the risk of COVID-19 spreading.

Ask yourself:

  • Can you see open doors and windows, fans that are on, or streamers moving on air conditioning vents?
  • Is there an air purifier placed in the room?

Some businesses may have signs or carbon dioxide (CO2) monitors to indicate ventilation.

Use the '3 Cs'

Assess the risk of COVID-19 transmission in any room or space by asking yourself if it is:

  1. Crowded?
  2. Close contact (for example, face-to-face conversation)?
  3. Confined or enclosed?

The more times you answer 'yes', the higher the risk of transmission.

This is because a mix of factors affect the risk of someone in a room or space becoming infected with COVID-19, such as:

  • the amount of COVID-19 virus in the air, which goes up with the number of infected people in the space, the type of activity (silent, speaking, shouting or exertion) and the amount of virus they may be breathing out
  • the size of the space
  • the time it takes for new air to replace stale air (the clean air change rate)
  • the length of time people have been in the room or space.

That’s why the risk of transmission is highest where there is an overlap of the ‘3 Cs’.

Ask yourself:

  • Are there people who have tested positive to COVID-19 in the space? Your risk of getting COVID-19 increases the longer you spend in a room with someone with COVID-19. For example, an indoors family gathering or a two-hour meeting in a conference room.
  • Are people speaking loudly, shouting, singing, or exerting themselves? Your risk of infection increases when a space is louder and people are more active. For example, people at a gym, or speaking loudly at a restaurant can spread COVID-19 aerosols into the air.
  • Is the room small? The risk of getting COVID-19 is higher in small spaces where people can’t maintain physical distancing of 1.5 metres. For example, patrons gathering at the counter of a small shop.

Video - Why is ventilation important

How to improve ventilation at home or in the workplace

There are simple steps you can take to ventilate your home and prevent COVID-19 virus aerosols from accumulating inside.

To ventilate your home or workplace, you should:

  1. Let fresh air in.
  2. Improve airflow.
  3. Filter the air.

1. Let fresh air in

An open window with fresh air coming inside

Bringing outdoor air into your home is the simplest way to ventilate your home. If it is safe, open doors and windows to bring outdoor air in.

Natural ventilation is especially effective when air can flow across indoor spaces, so try to open doors, windows, and vents on opposite sides of a room or corridor.

While it is better to open windows as wide as possible, even having a window open slightly can help.

Remember to leave internal doors open in hallways and corridors.

During colder months

There is an increased risk of COVID-19 spreading in the cooler months because windows and doors tend to be closed and people gather indoors.

You should still try to open windows where practical, even if only for 10 minutes each hour or when a room is empty.

Your comfort and safety should remain your priority.

2. Improve airflow

A fan blowing circulating air

You can use existing heating and cooling systems to help circulate air in your home and prevent COVID-19 aerosols from accumulating. It is best to use options that circulate fresh air into the room.

Split system air conditioners

Split system air conditioners circulate air in a room but do not bring in fresh air. Most home air conditioners are split system. If you have a split system, keep it on, but keep a window, vent or door open too to bring in fresh air. Use the ‘on’ mode rather than ‘auto’ mode for best results.

Evaporative cooling and ducted systems

Some older evaporative cooling systems and ducted systems bring in air from outside. Some windows or doors need to be left open for these systems to circulate fresh air effectively.

Run evaporative coolers or ducted systems once or twice a day in ‘fan-only’ mode to flush rooms with fresh outside air.

Heating and cooling systems need to be serviced regularly to make sure they are running effectively.

If you are using a ducted system or air conditioner, change the filter regularly according to the manufacturer’s instructions.

Some buildings have commercial ventilation systems that require specialist knowledge to operate. Building owners should get advice on how to increase fresh air circulation and filtration in these systems.


Fans can be used in addition to other methods to reduce the build-up of COVID-19 aerosols, especially in areas with poor airflow.

Fans circulate air in a room but do not provide fresh air. Fans work best when used alongside open windows, vents, or doors to bring in fresh air.

Turn ceiling fans on a low setting or use a pedestal fan in ‘swing’ mode to help air circulate.

Place pedestal fans near an open window, if possible, but point them away from people so they do not blow air directly onto others.

3. Filter the air

An air filter in operation

Portable air cleaners (filtration units, scrubbers, or purifiers) use filters to remove aerosol particles and other contaminants and release clean air.

Air cleaners are useful when existing heating and cooling systems do not bring fresh air into a space.

Put air cleaners in places where there is the least ventilation, away from windows, vents, fans, and grilles. Place the unit so the air intake is clear of obstructions.

Always choose the highest flow setting (when noise levels allow) and, if possible, keep the unit on for at least two hours after a room has been used. Check manufacturer instructions to make sure your air cleaner is big enough for the size of the room.

What if you can’t change ventilation in an indoor space?

If you can’t change ventilation in your indoor space, consider reducing risk by:

  • moving any gatherings with more people to an outdoor location
  • reducing the number of people in an indoor space at any one time
  • reducing the length of time people spend indoors together
  • avoiding peak activity times and places where people gather indoors
  • wearing a well-fitted face mask when indoors
  • optimising ventilation by periodically opening a window (for example, every 10 minutes at every hour if the weather is too cold or supervision is needed near an open window).

A carbon dioxide monitor

A personal carbon dioxide (CO2) monitor is a small portable device that measures the amount of carbon dioxide that people have breathed out into a room or space.

CO2 monitors can help you decide if a room that appears low risk might carry a higher risk. These include spaces that have few people or low activity, such as some offices or libraries. A high CO2 reading suggests the ventilation is poor.

CO2 monitors are not useful where there are a lot of activity and people moving over short periods of time, such busy cafés, or gyms. These are already higher risk environments.

There are limitations to their use. CO2 monitors don’t measure the COVID-19 virus in the air and don’t account for the effect of filtration or masks.

You can buy CO2 monitors at some stores and online. Use according to the manufacturer’s instructions.

Businesses may consider CO2 monitors to identify ventilation dead zones or use other monitoring systems. These other systems may be complex and require specialist advice.

More information for workplaces

Good ventilation is essential to keep workers, customers and the public safe. Workplaces with crowded or high-traffic areas can carry a higher risk of COVID-19 transmission.

For general information and guidance to help workplaces incorporate ventilation into their COVIDSafe Plan, see Ventilation in the workplace.

Different types of businesses need different types of ventilation strategies and have differing requirements. To learn more about ventilation in your business, see:

More information:

Reviewed 03 November 2022

Coronavirus Hotline

Call the Coronavirus Hotline if you have any questions about COVID-19.

The Victorian Coronavirus Hotline diverts to the National Coronavirus Helpline every night between 4pm and 9am.

Please keep Triple Zero (000) for emergencies only.

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