Ventilation and Virus Transmission – COVID 19


Ventilation plays an essential role in creating a safe and comfortable indoor environment. In a building people run the risk of reducing indoor air quality and using the out-door air as a method of ventilation through opening a door and a window is currently not an option since this has a higher risk of transmitting viruses. So, does a ventilation system itself help spreading diseases like COVID 19, or does it help us to avoid it? 


Researchers currently show that the Coronavirus mainly spreads through large droplet transfer (e.g: when someone sneezes and it’s catched by another’s respiratory system). This means that droplets caused by coughing or sneezing remain airborne for a fairly long time. Studies right now show that one can infect another from a distance of 2 meters. This is the reason why we have been practicing social distance at 2 meters. 

Another mode of transmission is surfaces. Here studies show that a person can infect another through, for example, coughing into their hand and then leaving the infective material on the touched surface. The next person that then touches this surface runs a high risk of being infected by the virus if they touch their mouth or eyes.

But the big question that we have been asking ourselves is if there is any potential of airborne transmission? Is there perhaps a chance that the virus included in the droplets could stay airborne for a long time? After the necessary research we found out that studies right now show that the virus possibly remains alive in normal indoor air conditions for up to 3 hours, and for about 2-3 days on indoor surfaces. So we conclude that it is possible that viruses, like COVID 19, can be transmitted through airborne transmission. 

The new questions that arose from this conclusion is: 

  • Do ventilation systems help spread viruses like COVID 19? 
  • If it is so, what tools can be used to avoid the spreading? 

After the necessary research we found that there is no scientific proof that COVID19 can be transported through ventilation systems. But most experts actually indicate that we should run our ventilation systems even more during periods of disease. We will now explain the methods that are proven effective to secure good indoor air quality by controlling airborne viruses like COVID 19. 



First of all, to bring in more outside air in buildings through a completely fresh ventilation helps with 

First of all, it helps to bring in more outside air into the building if we do so through a completely fresh ventilation system since it helps with diluting the airborne particles which in return makes an infection less likely. A study published in 2019 found that ensuring even the minimum level of ventilation reduced the virus transmission to as much as 60 percent. 

It’s because of this a recommendation that buildings with mechanical ventilation systems extend their operation times. You do this by simply extending the clock times of your system’s timers to start a couple of hours earlier than usual, and end a couple of hours later than usual. However, an even better solution is to keep the ventilation on 24/7, with reduced ventilation rates when people are absent. 

Ventilation systems can be broadly categorized in two categories: constant volume (CAV) and variable air volumes (VAV). In CAV-systems it’s recommended to raise the airflow volume if possible. But for VAV-systems that are controlled by using some kind of method to sense the number of people currently in the building, it’s a good idea to raise the minimum airflow during these times to make sure that the building is cleansed from airborne particles during unoccupied periods. 

To another point, it’s not uncommon that recirculation of air is used in a ventilation or air conditioning system, but this obviously raises the risk of spreading the virus since the same air is reused. By totally eliminating recirculation of air and limiting the use of mixing fresh air with recirculated air we minimize the risk of transmitting the virus in a building. 

To make sure that the ventilation system is in the highest condition it’s also important to avoid the possible risk for ‘’external recirculation’’. This is when the exhaust air from the building is remixed with the intake air on the outside. This is avoided by making sure that there is enough distance between discharge and intake, taking prevailing wind direction into account. 



Humidity has a proven effect on how viruses spread in buildings. There are a bunch of different theories of how, but it’s totally clear that humidity plays an important role. The recommandation has for a long time been that we should keep the lowest relative humidity between 40 and 60 percent for two major reasons: 

  1. Airborne viruses have the hardest time to survive under this condition
  2. Our bodies have the easiest time to resist viruses at this intervall of humidity. 



All filters that remove particles from the air have a certain potential to lessen the exposure for airborne particles like COVID 19. The question lies in what efficiency the filter needs to have to be effective and have a significant effect on how likely it is for humans to be infected by the airborne virus. Filters are always designed to trap particles and contaminants from PM10, PM2.5 to PM1. So the lesser the contaminant is in its size the tighter the filter has to be. 

Within health care ventilation systems we have to make sure that viruses and other pathogens make it through our ventilation systems and in these cases we either use electrostatic filters or high-efficiency particulate arresting filters (HEPA filters). Electrostatic filters are superior in every way except for being more expensive in the initial investment, but HEPA filters are because of this more commonly used. Both of these do, however, effectively stop airborne viruses to enter the building. 



So, what do we need to do to secure proper ventilation that prevents viruses to spread inside of our buildings? 

  • Increasing the ventilation rate by time and/or volume
  • Minimize recirculation leakages 
  • Add/remove moisture from the building so that it’s in between 40-60 percent.
  • Install an electrostatic filter (or HEPA) to make sure that viruses doesn’t enter the building in the first place. 


So far no studies show that ventilation systems aids the transmission of airborne viruses in any shape or form IF they are installed properly. So keep on using your ventilation system and follow these guidelines to make sure that you stay healthy. If anything wasn’t clear or if you’d like further guidance in how to create the perfect indoor environment in your specific building, please don’t hesitate to contact us on one of our social media channels. 



  • Combating the virus in the air – CAMFIL
  • Microbiological cleanliness in the operating room – Preventing airborne contamination – Guidance and fundamental requirements – Swedish institute for standards
  • ASHRAE Position Document on Airborne Infectious Diseases
  • Coronavirus Prompts Response in HVAC Industry – Tagg Henderson
  • Ventilation and airborne diseases – WHO
  • Assessing the Dynamics and Control of Droplet- and Aerosol-Transmitted Influenza Using an Indoor Positioning System – Timo Smieszek, Gianrocco Lazzari & Marcel Salathé
  • How coronavirus spreads on a plane 2020 – National geographic



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