As coronavirus-related news grows heavier and the temperatures outside drop, it’s hard not to worry about what the next few months of the pandemic will look like.
Before we know it, heating systems will turn on in homes and commercial spaces across the Northern Hemisphere. Should we be concerned about the virus spreading through heating systems as we were with air conditioning?
Infectious disease experts and engineers shared their thoughts on the spread of COVID-19 and why we, thankfully, may not have to fear contracting the virus through HVAC systems this fall and winter.
Some experts say it’s unlikely you will contract COVID-19 through a heating system.
Although a small number of cases have occurred because of HVAC system airflow, it is not a common way to contract the coronavirus, said Rick Martinello, medical director for infection prevention at Yale New Haven Health. As a whole, the risk is very low and there is not much concern around virus spread through standard heating (and cooling) systems.
“The likelihood is that the dilution and filtration that occurs as air recirculates is likely sufficient to prevent most of the dispersion of virus in that way that would pose a threat to people,” he said.
But Martinello also noted that things can change quickly as we learn more about this coronavirus. “We don’t know if what I just said is absolutely true. But what people have experienced over the last eight to nine months has not raised concern that this is a major way that COVID is being transmitted.”
Fans could potentially be a culprit in COVID-19 transmission under the right circumstances.
James Lo, an assistant professor of architectural engineering at Drexel University, explained that HVAC systems designed for commercial spaces (like a mall or an office building) have filters and ducts that mostly clean the air before it recirculates. He added that HVAC systems also bring outdoor air into a space, which helps dilute the indoor air, making the likelihood of infection from an HVAC system pretty low.
But some people are worried about fans of any sort — HVAC fans, individual-use fans, standing fans — blowing air, and thus contaminated particles, away from a sick individual and toward other people.
“When you have a relatively large room and a system blowing air, there’s a chance a fan can blow droplets from one person toward somebody else. So, that is the key concern of how an HVAC system might impact airborne transmission,” Lo acknowledged. (And, as the Centers for Disease Control and Prevention now recognizes, COVID-19 can spread through the air.)
The professor stressed that this would likely happen only in a space that isn’t well-ventilated and only if the infected person is in front of the fan. He added that a lot has to go wrong for people to get sick this way — the virus is mainly spread when people are too close together for long periods of time, not when fans move droplets.
“I don’t want people to get paranoid,” he said. “The airborne phenomenon is very real ― people will get sick. But thinking you will get sick anywhere you are is not realistic, it’s just not true.”
Infection rates within households show the risk is low.
Amesh Adalja, a senior scholar at Johns Hopkins University Center for Health Security, encourages the public to look at household attack rates for the virus to refute any idea that COVID-19 spreads easily through heating systems.
“We’re not seeing widespread dissemination that would follow the pattern of it being in heating systems or in HVAC systems. Even in a household when you have an infected person, the attack rate is not 100%,” he said, meaning when one person in a household tests positive for the coronavirus, other people in the home do not always get sick.
That said, there is some disagreement about HVAC risk and we’re still learning about COVID-19 transmission.
Over the course of the pandemic, there have been corrections to guidelines, retractions from medical professionals and varied rules for mask-wearing state by state. So it’s not surprising that there is some disagreement around the risk of the coronavirus spreading through HVAC systems as well.
“There’s a professional debate about some of this that has gotten pretty heated between aerobiologists and infectious disease doctors,” Adalja said.
His best advice: people shouldn’t panic and should listen to infectious disease experts on what is known now while remaining flexible in their own thinking.
“I point to epidemiology. There are only a few case reports of things that might have been blown around by air currents — but it’s not that it’s getting sucked into the [HVAC] device and coming back out, disseminating everywhere,” Adalja said.
Key facts we have heard for months from experts remain true: The virus can be airborne and it largely spreads person-to-person amid unmasked get-togethers, lack of social distancing practices and improper hygiene.
Limiting your contacts is still advisable to prevent the spread of the illness. You should also consider opening windows in your home when you can and otherwise make sure your space is well-ventilated. Wipe down any high-touch surface areas that might be contaminated. And, most of all, wear a face mask.
Experts are still learning about COVID-19. The information in this story is what was known or available as of publication, but guidance can change as scientists discover more about the virus. Please check the Centers for Disease Control and Prevention for the most updated recommendations.