A Greater Emphasis on Ventilation And COVID: Understanding the CDC Guidelines

At a Glance

Early in the pandemic, there was a significant focus on cleaning and hygiene and less focus on protection from airborne transmission.  Indeed, back in March of 2020, neither the CDC or the World Health Organization (WHO) believed that SARS-CoV-2, the virus that causes COVID-19, was spread by airborne means. Somewhat later, CDC recommended an “all of the above” approach that continued to place emphasis on cleaning and disinfecting as they learned more about this novel (i.e. “new”) corona virus. 

Thinking about cleaning and disinfection is still important under certain circumstances.  For example, if someone in the workplace contracts COVID-19, it is important to consider cleaning and disinfection of their workspace.  However, we now know that SARS-CoV-2 primarily spreads through airborne particles.
Proper ventilation of indoor spaces, therefore, is a crucial factor in limiting infections and in workplace health. The CDC has developed in-depth guidance on ventilation, and there are some key lessons to take away.

Why Is Ventilation Important?

In areas where ventilation is poor, aerosolized particles can persist more easily and in higher concentrations, especially the very smallest particles. Proper air flow helps to reduce the concentration, but it does not prevent it completely. Physical distancing, proper mask use, handwashing and hygiene, physical barriers, and vaccination all also need to be a part of an overall workplace health strategy.

What Aspects Of Ventilation Do I Need To Focus On?

There are three points to consider when improving ventilation: 

  1. Increasing the amount of air that comes in from outdoors, 
  2. Increasing the total ventilation of a space, and 
  3. Filtering the air where possible. 

Ideally, airflow should be pulled from indoor areas and vented outdoors.  However, many ventilation systems – especially newer ones – are not designed to operate by pulling large volumes of air in from the outside.  This presents many technical challenges that are often site-specific and must be addressed based on the individual air flow of a facility.

Can SARS-CoV-2 Spread Through Ventilation Systems?

Research is ongoing into this question. While viral RNA has been found in some ducts and filters, the presence of RNA does not necessarily indicate a viable virus particle. As of this writing, the RNA found does not indicate a level capable of transmitting disease.  To put this in context, viral RNA has also been found on surfaces inside COVID-19 patient’s hospital rooms, and even in those scenarios it is unclear whether, or how much, they contribute to new infections.

An ultraviolet light germicidal irradiation system (UVGI) can be installed in ventilation systems to kill any microbes that may be present in a ventilation system. However, these need to be carefully managed to limit human exposure to UV radiation.

What Tools Do I Have To Improve Ventilation?

Any ventilation system will need to be changed with an eye to the health of the entire building. For example, if you place a fan in every doorway, yet those fans point into a hallway with poor ventilation, particles will collect in that hallway. Each facility is unique and will need a different strategy to manage the movement of “clean” air in, “less-clean” air out. That said, many of the tools to implement this strategy will already be familiar to you.


  • Windows: Simply opening a window, where possible, can assist with airflow. This must be balanced against other concerns, however, such as vehicle exhaust that may collect in certain areas.
  • HVAC Systems: Running systems at maximum two hours before and two hours after occupancy of a facility can help circulate air. Configuring systems to run on high, instead of automatically, can also improve overall airflow.
  • Fans: Appropriately placed fans can encourage airflow. However, overall airflow design has to be considered. Fans also should not be set on a high speed or pointed towards areas that may be regularly occupied.  One exception is exhaust fans that have already been installed. These should be run per your facility’s HVAC plan while the building is occupied, and regularly examined and maintained.
  • Portable HEPA Filtration Units: High Efficiency Particulate Air filters are approximately 99.97% effective at capturing particles. To put that in context, the main type of respiratory protection used to protect against inhaling aerosols (the N-95 or KN95) are 95% effective at capturing particles.  HEPA units are generally sized for small rooms and while they shouldn’t be considered a replacement for outdoor ventilation, can assist in air quality in spaces such as contained rooms without other airflow options. 

As recently as April 5th, the CDC estimated that the chance of contracting COVID-19 through surface transmission is lower than 1 in 10,000, so if you are still placing most of your firm’s emphasis on cleaning and disinfecting workplaces and ignoring your HVAC systems, reconsidering your COVID-19 prevention strategies is likely warranted.

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