Row of air conditioning units

Updated November 9, 2020

The CDC has updated their guidance to say that COVID-19 can be spread through airborne transmission. Modern HVAC systems can limit indoor spread by exchanging and filtering air.  Poorly ventilated spaces may increase the risk of COVID-19 spread, including among people more than 6 feet apart.   

The CDC recommends improving HVAC exchange and filtration and maintaining everyday preventative measures like physical distancing, wearing face coverings, and hand washing. Businesses may want to implement flexible scheduling and sick leave policies for staff and health checks for staff and visitors. To learn more, visit the CDC’s Interim Guidance for Businesses and Employers page.

To reduce risk in older buildings with ventilation systems that recirculate air:

  • Open doors and windows, even when it’s cold outside. Ideally, open multiple points in enclosed rooms, so air can flow in and out. Use fans and air circulators to speed up the exchange of air through windows and external doors.
  • Use portable air purifiers with HEPA filters.
  • Use filters with a Minimum Efficiency Reporting Value (MERV) rating of 13 or higher in the building’s HVAC system.

ASHRAE Guidance

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has developed guidance and reopening recommendations. They focus on large buildings with complex HVAC systems. 

ASHRAE recommends designers of new and existing HVAC systems go beyond minimum standards to control the spread of COVID-19. 

Guidance for Reopening Office Buildings

If you are resuming business operations after a closure, ASHRAE recommends the following:

  • Create a COVID-19 building readiness plan.
  • Have a qualified HVAC expert inspect the ventilation and analyze the system to ensure it meets at least the minimum recommended standards for air circulation and filtering.
  • Flush the building’s air before or very soon after the building is reoccupied.

For more COVID-19 guidance pertaining to office buildings, visit the CDC’s COVID-19 Employer Information for Office Buildings page.