Natural Ventilation


We know that outdoor interactions are significantly safer than indoor interactions and that meeting people outdoors can reduce the risk of transmission of SARS-CoV-2 by up to 20 times. Most of this is likely due to the good ventilation provided by being in the outdoor environment. We can recreate much of this by simply improving indoor ventilation.


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How do I improve natural ventilation?

Opening windows and doors helps introduce fresh air and expels stale air containing infectious aerosols. The more they are open and allow fresh air to flow across the room,  the better.

How effective this is depends on how much the windows and doors are open, and how much air flows through them which is dependent on weather conditions such as wind and temperature.


Cross Ventilation

Single Sided Ventilation 

Stack Ventilation


Carbon Dioxide Meter

Leonard Hammond


Raymond Clarke

Brand Expert

Is your natural ventilation is enough?

To determine whether natural ventilation is sufficient we can use the measured room levels of carbon dioxide produced by occupants as an indirect measure of the adequacy of the ventilation.

Carbon dioxide (CO2) monitors are small, cheap, readily available, and portable.

These should be placed at least 2m away from occupants and as far away from windows and doors as possible to get an accurate reading.


“Action limits should be applied as per below:

  1. Below 800 ppm – indicates a low relative risk of infection.

  2. Between 800 ppm to 1,500 ppm – indicates a moderate relative risk of infection. Improvements should be made where practicable to increase the provision of fresh air into the indoor space.

  3. Above 1,500 ppm – indicates a high relative risk of infection. Immediate improvements must be made to increase the provision of fresh air into the indoor space or air filters must be operational. If this is not possible, the space should be evacuated.

  4. Around 600 ppm or below is best practice.” – OZSAGE

Buy a CO2 Monitor


Natural Ventilation not reliable or inadequate?  


Mechanical Ventilation

Mechanical ventilation in some buildings may be adequate or can be modified to increase the amount of ventilation taking into account the number of occupants and type of activity that may require higher rates of ventilation.


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HEPA (Air) Filters

HEPA Filters have been shown to reduce the amount of virus containing aerosols in the indoor air environment and may be a suitable solution where mechanical and natural ventilation is inadequate


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