COVID-19: Improving indoor ventilation

Good ventilation helps protect against the spread of COVID-19. It replaces indoor air with outdoor air, which can reduce the number of infectious particles indoors. Air filtration can also help by removing particles from the air.

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How to improve indoor ventilation

The larger a gathering, the more likely it is that someone with COVID-19 is present. When they breathe, they release infectious particles into the air. These particles build up faster in small indoor spaces.

Natural and mechanical ventilation help to reduce levels of infectious particles indoors. They do this by replacing indoor air with outdoor air. A well-ventilated room doesn't feel stuffy or smelly.

Combined with individual public health measures, good indoor ventilation helps prevent the spread of COVID-19.

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Natural ventilation

Open windows and doors regularly, when possible, to improve natural ventilation. Opening multiple windows can help by creating a crossflow of fresh air. If windows have openings at both the top and bottom, open both for maximum airflow.

In cold or wet environments, or if safety or air quality are a concern, open doors or windows:

If there is cause for concern about the ventilation in a room or you can't open windows or doors:

Mechanical ventilation

Many buildings use a central heating, ventilation and air conditioning (HVAC) system for mechanical ventilation. If your indoor space has vents in the ceiling, walls or floor, then it probably uses an HVAC system.

Consult an HVAC professional to:

Do routine maintenance, such as:

If possible, run the HVAC system fan continuously. This will increase the delivery of clean air and reduce the number of infectious particles indoors.

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How to improve ventilation in specific settings

In addition to the general recommendations above, other measures can improve ventilation in specific settings, such as homes, long-term care facilities and schools.


Most homes use natural or mechanical (HVAC system) ventilation and should follow the recommendations above. You may also consider the following measures, particularly when visitors are present.

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Long-term care facilities

Most large buildings have an HVAC system. The maintenance staff and operators of these buildings should understand how the HVAC system works, and how to maintain it. In addition to the recommendations for natural and mechanical ventilation above, they should:

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In addition to the recommendations above, staff may consider:

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Portable air purifiers

Air purifiers are also known as portable air filtration devices. When used properly, they can reduce the amount of some viruses in the air. When choosing an air purifier, select a unit that's:

Using an air purifier indoors may add an additional layer of protection. However, it should be used along with other individual public health measures.

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Fans and single unit air conditioners

Portable fans, ceiling fans, and single unit air conditioners typically circulate the air within a room, but they don't exchange air. They can propel the virus far from its source, thereby increasing the risk of infection transmission.

If using these units, make sure the air stream doesn't blow directly at or between people.

Carbon dioxide (CO2) monitors

People are the main source of CO2 indoors, beyond the background levels in our atmosphere. We release CO2 into the air when we exhale. When indoor levels of CO2 are high or increasing, it may mean that there isn't enough ventilation to clear exhaled air from a space.

Existing standards and guidelines for indoor CO2 levels are based mostly on how the room smells and feels. They aren't based on the health effects of CO2 or the risk of disease transmission.

A low level of CO2 in an indoor space doesn't necessarily mean transmission risks are low. CO2 levels alone don't reflect all transmission risks. For example, they will not indicate if someone who has COVID-19 is present. Additionally, CO2 levels will not reflect of the use of other public health measures, such as wearing a mask, or reflect ventilation improvements that may result from air filtration measures taken.

 Appropriate CO2 monitoring requires:

For a CO2 monitor to be a useful indoor air quality tool, you must act when levels are high or increasing. For example, you could:

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