CDC: Aim for 5 Air Changes Per Hour in Buildings

Updated: May 16, 2023

On May 12, the Centers for Disease Control and Prevention (CDC) updated its "Ventilation in Buildings" guidelines to include a discussion on "How much ventilation is enough?" to help prevent airborne disease transmission.

"When possible, aim for 5 or more air changes per hour (ACH) of clean air to help reduce the number of germs in the air," the CDC advised building owners and managers.

On May 15, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), a professional society that sets heating, ventilation, and air conditioning (HVAC) standards, released a draft of a standard for maintaining healthy indoor air quality (IAQ). The ASHRAE is accepting comments on its draft 241P-202X Standard, Control of Infectious Aerosols, through May 26.

The draft ASHRAE Control of Infectious Aerosols standard would provide minimum requirements for HVAC-related measures to reduce the risk of transmission of COVID-19, influenza, and other airborne viruses in homes, hospital offices, and schools during periods of high transmission risk.

In addition to a five ACH ventilation recommendation, changes to the CDC's ventilation and air filtration guidelines include the following:

The CDC recommended that building owners and managers take the following four steps to improve air circulation in buildings:

The CDC's recommendations for improving air cleanliness included:

The CDC acknowledged that DIY air cleaners, when built and used correctly, can provide a temporary intervention for reducing COVID-19 transmission, but it cautioned that DIY air cleaners are only appropriate during emergencies or for short-term use, such as when obtaining commercial air cleaners isn't possible, not as a permanent, long-term solution.

A common DIY design is a cube made of MERV-13 (or better) filters as the cube's sides and bottom and a 20-inch box fan attached on top. The EPA is studying the use of DIY air cleaners to reduce wildfire smoke indoors.