May 18, 2023

CDC's New Building Ventilation Guidance Calls for 5 ACH, Upgraded Filters

New CDC recommendations for improving ventilation in buildings urge owners and operators to aim for at least 5 air changes per hour (ACH) in occupied spaces and to upgrade filters to those rated MERV-13 or higher. The agency stresses the importance of good ventilation in maintaining healthy indoor environments and protecting building occupants from respiratory infections, including COVID-19.

CDC’s guidance outlines basic strategies—such as regularly changing filters in HVAC systems and ensuring that filters fit properly in the filter racks—as well as “enhanced strategies” for improving buildings’ ventilation, filtration, and air treatment systems. According to the agency, enhanced strategies are those that can help lower the concentration of viral particles in building air. In addition to delivering 5 or more ACH per hour and upgrading filters, these strategies include setting a building’s HVAC system to circulate more air when people are inside; bringing in clean outdoor air by opening windows or doors and using exhaust fans; and using air cleaners with high-efficiency filters to filter air. CDC also recommends that building owners and operators consider installing UV air treatment systems and using portable carbon dioxide monitors to help assess whether indoor air is stale or fresh. CO2 readings above 800 ppm suggest that more fresh, outdoor air may be needed in a space, the agency says.

CDC also updated another webpage on ventilation in buildings to reflect its recommendations regarding ACH and minimum efficiency reporting values for filters. Other new information that can be found on this page includes updated agency guidance on post-occupancy flushing of building air, cost considerations for ventilation strategies, and a discussion of whether do-it-yourself (DIY) air cleaners are effective at reducing the risk of COVID-19 transmission indoors.

These updates accompany changes to CDC’s monitoring strategy for COVID-19 following the end of the national public health emergency on May 11. Further details can be found on CDC’s pages on improving ventilation in buildings and ventilation in buildings.