Does air-conditioning spread coronavirus in gyms, stores, and restaurants? Experts weigh in.

• After a research letter found that air conditioning blew droplets around a restaurant in China, infecting three families, people began wondering if air conditioning could spread infection.
• Experts say in commercial buildings, ventilation systems should use outdoor air if they can.
• HVAC industry association REHVA told its engineers to stop recirculating air in buildings where there had been an outbreak of COVID-19, the disease caused by the coronavirus.

Forecasters are saying the heat is going to be scorching in America this summer, and some experts are wondering what this means for commercial businesses contemplating reopening.

Gyms have outlined a range of measures to make their spaces safer. Gold's Gym suggested spacing treadmills further apart. Anytime Fitness will place markers on the floor so people stand far apart. Equinox's executive chairman Harvey Spevak said they are not opening yet, but he expects they may ask people to book time in the gym, to limit capacity.

None of the re-opening gyms have touched on the subject of what they will do about air conditioning, nor have the retail stores, movie theaters, and social clubs that are will soon be accepting customers in states like Georgia and Idaho.

But a study, published in early April, has raised questions about whether those plans should take air-conditioning into account.

According to the report, nine people were infected with the coronavirus in mid-January after dining on neighboring tables in the same restaurant in Guangzhou, China. The researchers concluded one of the diners had an asymptomatic case, and the air-conditioning unit blew her viral droplets across the room.

The research triggered different responses from the boards that advise the air-conditioning industry.

In the US, ASHRAE said AC units should not be shut down in the summertime, writing: "Unconditioned spaces can cause thermal stress to people that may be directly life threatening and that may also lower resistance to infection."

Their European counterpart (REHVA) said the opposite: they told engineers to stop recirculating air in buildings where there had been a COVID-19 outbreak.

According to scientists who study ventilation, both of those perspectives are valid. Here's what business owners should consider:

Keep windows open, or use an AC unit that brings in air from outside

In a recent study, researchers at the University of Oregon and the University of California, Davis, teamed up to study how to limit the spread of the novel coronavirus in built environments. They concluded, much like REHVA, that the safest way to ventilate a space is to open a window.

"The droplets that may have viruses follow the air very easily so they will go right out the window," said Ana Rule, assistant professor at the department of Environmental Health and Engineering at the Johns Hopkins Bloomberg School of Public Health.

Qingyan Chen, a mechanical engineering professor at Purdue University, agrees. Where it's not possible to open a window, Chen recommends that supermarkets, gyms, movie theaters, and other commercial buildings supply their ventilation systems with 100% outside air, which is filtered before blown into the building — as opposed to recirculating the air existing within the building.

That existing air could carry disease, especially given the high proportion of asymptomatic spreaders of the coronavirus.

One business has taken the precautionary step of closing public spaces that are AC-equipped.

As early as March 13, Alex Kalajian, COO of Solstice Residential Group, wrote in a memo to over 80 New York apartment buildings that he manages that they should close all spaces equipped with centralized AC. That includes saunas, pools, gyms, and conference centers.

Kalajian, a qualified industrial hygienist, told Business Insider he agrees that it is a drastic move, but his concern is that, in most buildings, the return vents for amenity rooms are located in the basement.

"I looked at peer reviewed studies of what occurred during the initial the SARS virus outbreak in 2003, and those studies pointed to the potential spread of the virus through HVAC systems and plumbing stack lines," Kalajian said.

Ventilation is key when there's a lingering virus, but it can't get too cold

There is merit to the idea that air-conditioning is helpful during a pandemic, as the US board ASHRAE said.

Overheating can be dangerous for people exposed to a virulent virus.

What's more, a 2019 study found that even a small amount of proper ventilation in a building had the same effect as vaccinating 50% to 60% of the people in the building for influenza. Proper ventilation reduces the possibility of getting infected via disease-laced droplets or the air-borne diseases which can exist in an unventilated room for lengths of time. This makes opening a window a quick, easy way to control disease spread.

However, it's important to keep buildings a few degrees warmer than normal.

Research suggests that the virus doesn't last as long in hotter temperatures. Rule recommended keeping the thermostat between 70 to 75 degrees.

Some experts say: don't worry about AC, focus on keeping your distance from other people

Some health officials, including New York City's Department of Health, say the risk of viral spread through AC units is low.

In air-conditioned public spaces like grocery stores, the best and only thing you can do is stay away.

"If you have no control over the air-conditioning, assume that the person that is close to you is sick," said Rule. "Stay away from that person. Wash your hands every time you touch a surface, don't touch your face."

Epidemiologist Meghan May, a professor at the University of New England College of Osteopathic Medicine, said that keeping physical distances is a far more important consideration than worrying about ventilation.

"I'm not yet convinced it is a concern," May told Business Insider. "But if it is, I would say air-conditioning is the least of your worries in mass transit or apartments."

William Bahnfleth, director of indoor environment at Pennsylvania State University, agreed.

"Infection control usually doesn't have a silver bullet," Bahnfleth told Air Conditioning, Heating & Refrigeration News.

"Things like hygiene, being careful about whether you touch your face, whether you're shaking hands with people, whether you're washing your hands frequently — those, in many ways, are just as important as doing the right things with your HVAC."