The importance of building ventilation


Ventilation is the deliberate introduction of fresh air and removal of stale air from a space.

Proper ventilation is an important approach to lowering concentrations of indoor air pollutants or contaminants including any viruses that may be in the air.

The general purpose of ventilation in buildings is to ensure that air in the building is healthy for breathing.

Why ventilation is important to reduce the spread of viruses

Transmission of some viruses is more common indoors, where there may be less space to physically distance, and where people may come into contact with droplets and aerosolised particles more easily.

The virus that causes COVID-19 can be spread from person to person through contact with droplets, which are produced when a person sneezes or coughs, or through other small respiratory particles that are produced when people talk, sing or shout. These small particles (smaller than five microns) can become aerosols and remain in the air for some time, potentially travelling farther than droplets.

Aerosolised particles may build up if there is not enough ventilation.

Open or well-ventilated spaces reduce the risk of transmission of COVID-19 because infectious particles are more quickly diffused in the open air than in spaces with less ventilation.

Proper ventilation also reduces surface contamination by removing some virus particles before they can fall out of the air and land on surfaces.

How to improve ventilation

To help reduce the risk, it is important to take steps to improve ventilation in indoor settings so that any infectious particles that may be present in the air are more quickly removed.

The general rule is the greater the number of people in an indoor environment, the greater the need for ventilation with outdoor air. Therefore high-traffic areas should have additional ventilation.

Ways to safely improve ventilation include to:

  • open windows and doors to increase outdoor airflow (Do not open windows and doors if doing so poses a safety or health risk (e.g., risk of falling)
  • ensure that heating, ventilation and air conditioning (HVAC) systems are well-maintained and operating properly
  • make sure air filters are properly sized and within their recommended service life.
  • avoid using only recirculated air in HVAC systems, and increase the outside air intake
  • consider disabling ventilation controls with automated settings that reduce air supply based on temperature or occupancy
  • ensure exhaust fans are operational if in place (i.e. ensure car park exhaust fans and common property bathroom exhaust fans are functional and operating at full capacity)
  • avoid directing fans towards people’s faces, such as by aiming them continuously towards the ceiling or floor. Limit oscillation and turbulence of fans
  • increase ventilation during and after cleaning, for example, open windows and doors, to reduce risks from particles resuspended during cleaning

The use of C02 metres to measure air quality

Carbon Dioxide metres can give an indication of how much air you are breathing that is coming out of other people’s respiratory systems.

According to experts on air quality, when using a carbon dioxide metre, anything below 500ppm in a room means ventilation is good.

At 800ppm, it means 1% of the air, someone is breathing air that has already been exhaled by someone else. To keep the risk of Covid low. Co2 levels should be well below 700ppm.* (The Economist)

Article Sources

NSW Health Ventilation Guidance

Centre for Disease Control and Prevention (US) 

Surface to air transmission_The Economist Article, May 29 2021

Ventilation Problem_New Scientist article, 21 August 2021

Useful Links

WHO – Roadmap to improve and ensure good indoor ventilation in the context of COVID-19


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