Understanding Your Ventilation System

By: Allen M. Chung, CIH and Paul Linnartz

As people start to return to office buildings and public areas after a year of “pandemic life,” there will undoubtedly be a heightened awareness of air quality in closed spaces.

SARS-CoV-2, the virus that causes COVID-19, is known to spread through aerosolized respiratory droplets at close range. Airborne transmission from exposure to very small droplets is unlikely over long distances but possible in certain indoor spaces. General ventilation typically addresses common contaminants often found in commercial environments, but many of these commercial systems have not been designed to protect occupants from the SARS virus.  Understanding a facility’s general ventilation system is an essential step toward improving indoor air quality as well as moderating the risk of COVID-19 at your facility.

To moderate the spread of COVID-19 in an indoor space, a recent article published by the National Center for Biotechnology Information (NCBI) recommends the following:

  • increasing air exchange rates above current conditions
  • using high‐efficiency filtration for recirculated air (MERV 13 or higher)
  • verifying that sensitive areas, such as bathrooms and rooms where infected patients are cared for in hospitals and senior homes, are negatively pressurized relative to adjacent areas
  • managing airflow direction and speed to prevent the spread of aerosols across occupants
  • considering additional technological controls, such as UV germicidal irradiation and portable air purification, in areas and situations where typical building‐level controls are not sufficient


Ventilation effectiveness is measured in terms of Air Changes per Hour (ACH). By running the recirculated air through high-efficiency filtration (MERV 13 or higher), possibly adding UV germicidal irradiation, and/or portable air purification units, more “clean” air is provided to the indoor space. The amount of clean air needed can vary widely depending upon building design and occupancy. ASHRAE, which sets ventilation standards and guidelines, recommends ACH levels up to 3x/hr for offices, 6x/hr for schools, and 8x/hr for restaurants.


Do you know what your ACH rate is?


Evaluating air exchange rates (ACH), checking negative pressure at sensitive areas  and mapping airflow direction and speed in your facility can determine whether your ventilation systems promote healthy indoor environmental conditions. This can be a complicated process.  Please reach out to if you need assistance.  Let’s work to end this pandemic!