Can Air Conditioning Spread COVID-19?

What to know about the AC units in your home, and air conditioning in your office, restaurant, gym, or other public spaces.

Now that warmer weather is on the way, people are wondering: Can air conditioning spread COVID-19, especially the AC in public places, like your office or a restaurant?

Early research raised concerns. In the early months of the COVID-19 pandemic, a study published in Emerging Infectious Diseases found nine people in Wuhan, China, were infected with the virus simply by sitting near an air conditioning vent in a restaurant. According to researchers, the virus was spread by one asymptomatic diner who sat at a table in front of the AC unit. Four people at the table later tested positive for COVID-19, as did five people at neighboring tables.

Manish Butte, PhD, an associate professor in the department of microbiology, immunology, and molecular genetics at the University of California, Los Angeles, tells Health that within a public setting, like a restaurant, workplace, or gym, air conditioning might be potentially risky. It has to do with the way AC works. Air conditioning circulates air more rapidly, which removes humidity. Water vapor can hold onto heat, so with less of it in the air, once the humidity is removed, a room or space cools down. "Less humidity in the air promotes evaporation, which causes droplets in the air to dry up and disappear," says Butte.

It helps to understand a little about droplets. Droplets contain mostly water, but can also contain pathogens, such as the COVID-19 virus. We spread droplets when we breathe, talk, cough, sneeze, and do other activities that involve exhaling. For example, one cough can release 3,000 droplets, and it is estimated that a sneeze can release around 40,000 droplets.

Different actions produce different sizes of droplets, which can travel varying distances. When an AC unit is turned on, air flow from the vent pushes these droplets through the air and potentially into other people. "The air flow direction is what matters," adds Butte.

Erin Bromage, PhD, a Comparative Immunologist and Professor of Biology at the University of Massachusetts Dartmouth, believes that ventilation issues in indoor spaces with lots of people, such as crowded restaurants, are concerning from a transmission standpoint. And Butte agrees that air conditioning can make droplets containing infectious virus particles spread farther. Remember, while air conditioning might make a room feel fresher on a warm day, it's recycled existing air.

Regarding the restaurant study mentioned previously, it's important to consider that it had a small sample size and didn't replicate conditions in a lab. "I don't necessarily think that this study is representative of transmission risk," infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security in Maryland, tells Health. "However, it is important to be mindful of airflow patterns, especially if they are strong and create a jet stream for droplets."

So should we all be ditching our air conditioning systems until the threat of COVID-19 has passed? In a word, no. Air conditioning in your own home is far less risky than AC in a busy public place if you've been following recommendations regarding hygiene. If you haven't had a stream of people in and out of your home, the only droplets that could be spread by air conditioning are those from you and whoever else is in your home. "Within a home, where everyone is highly exposed to each other, there isn't a need to worry about air conditioning," says Butte.

As for air-conditioned offices, malls, and restaurants, know that a risk exists, but most experts are not saying that you should refrain from venturing into public places. Spending time in any indoor space outside your home requires a certain level of risk assessment. If you go to a restaurant or any other busy place with air conditioning, continue to follow the CDC's current practices for preventing the spread of COVID-19. This may vary depending on where you are and likely involves measures such as social distancing, hand-washing, not touching your face, and, as always, staying home if you feel sick or have symptoms of COVID-19.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.

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