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Airborne transmission of coronavirus has made high-end air filtration systems more popular than ‘toilet paper in April’ as HVAC systems sell out

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Jim Rosenthal, CEO of Tex-Air Filters, is so overwhelmed with orders for air filters that he has “to turn customers away.”

Ever since the summer, he said, “the phone’s been ringing off the hook” with calls from businesses, schools and universities hoping to upgrade their air filtration systems to combat the coronavirus.

“I’ve been in this business for 20 years and this is the most chaotic time that I’ve ever had in the air filter business,” he said in a phone interview. He added that sales are up by about 15% year over year, but they would be even higher if the Fort Worth, Texas-based manufacturer could keep up with all of its orders, he said.

Like so many products suddenly in hot demand due to the pandemic, high-quality air filters are also flying off the shelves, causing a backlog of more than a month for some customers, Rosenthal said. “It’s like toilet paper in April times two,” he said.

Nearly all of the demand has come from commercial customers seeking to allay fears of indoor spread of the coronavirus, Rosenthal said. Evidence has been mounting for months that the virus can spread by air, but effective and high-quality air filtration as well as proper ventilation can reduce the risk of spread, airborne pathogen specialists say. It’s no silver bullet, but as the weather turns colder and people spend more time indoors, it’s another layer of a multi-pronged defense against the virus.

Last week, the Centers for Disease Control and Prevention revised its guidance on the coronavirus, acknowledging that in certain environments, the virus can spread more than 6 feet through airborne particles that linger in the air.

The CDC maintained that the dominant route of transmission is through respiratory droplets people produce when they cough, sneeze and speak. But it was the first acknowledgement of another route of transmission: smaller particles called aerosols.

‘You can filter aerosols’

Kimberly Prather, a distinguished professor of atmospheric chemistry at the University of California at San Diego, said the acknowledgement was a long time coming. She’s been advocating for public health officials to acknowledge airborne spread for months.

“You can filter aerosols. That’s the beauty of it,” she said. “You’ll hear, and it’s incorrect, ‘oh, these viruses are too small to be filtered,’ but that’s not true. They’re perfect. They’re very easily filtered out.”

Prather added that proper filtration and ventilation shouldn’t be viewed as a silver bullet that totally and immediately eliminates the virus. Proper filtration, though, is a key part of a layered defense that includes, first and foremost, mask wearing, social distancing and the frequent washing of hands, she added.

Tex-Air Filter’s Rosenthal, who previously served as president of the National Air Filtration Association, said his company provides both industrial filtration systems for businesses and schools as well as portable filters mostly for consumer use in households. A lot of the new demand, he said, is coming from businesses that want to upgrade from a basic heating, ventilation and air conditioning, or HVAC, system to a highly efficient one. The most demanded products now are at the grade of MERV 13, which most atmospheric chemists agree can likely filter out particles the size of the aerosolized coronavirus.

Upgrading HVAC

Jeff Siegel, a professor of civil engineering at the University of Toronto and a specialist in indoor air quality, ventilation and filtration, said people have been overlooking air quality and HVAC systems for a long time “and now we’re paying a price for that.”

“You might be talking about 100-year-old school, you might be talking about a postwar apartment building, you might be talking about a brand-new condominium or office building,” he said. “We’ve got to get fresh air into those spaces and when you can’t get fresh air, you have to do other things, maybe portable filtration, maybe limiting how that space is used.”

Siegel said every office building, business, apartment building, school and other congregate space should measure the ventilation levels in every part of the building. Managers should clearly communicate where ventilation is strongest and weakest, Siegel said, and try to improve the levels overall by opening windows and doors, and upgrading HVAC systems with better filters, he added. Just as important, he said, the HVAC equipment needs to be installed correctly and frequently maintained.

Germicidal UV?

Shelly Miller, a mechanical engineering at the University of Colorado Boulder, has experience consulting with homeless shelters to improve their HVAC systems and reduce the risk of spreading airborne infectious diseases like tuberculosis. She said there’s no one-size-fits-all approach to reducing the risk of transmission. One approach she found useful in large, high-risk gathering spaces is systems that use germicidal ultraviolet light, though she doesn’t recommend that in most facilities.

“You can hang these lamp fixtures on the wall in the space or from the ceiling in the middle of the room and they generate a band of UV just in the upper part of the room,” she said. “In the lower part of the room are the occupants and if they’re talking and speaking, their respiratory droplets will mix into the air and move up into the ceiling and be irradiated in the ceiling part of the room.”

That might be ideal for high-risk environments with high ceilings and few windows to improve ventilation like some cafeterias, she said, but UV brings its own risks of harming health, especially if not installed properly.

Limited airborne spread

Dr. Bill Schaffner, an epidemiologist at Vanderbilt University, maintained that aerosol spread of the coronavirus is “rather uncommon” and the potential risk reduction from wide use of air filters is somewhat limited.

“If we thought airborne transmission were notable, then there would be a much larger call to critically evaluate air handling systems, all the way from homes to malls, to churches, to places of business,” he said. He added, however, that it’s still “worth looking at your air handling system,” especially for businesses and schools that are trying to bolster public confidence.

Schaffner said the best way for individuals to reduce their risk of infection is to wear a mask, wash their hands frequently and avoid those crowded, indoor spaces. In those indoor spaces, though risk of infection can be reduced by improving air filtration and ventilation by opening windows and doors, he said. Hiring an air conditioning engineer to ensure there are no “dead spots,” where air and thus the aerosol particles might linger, in one’s business or place of gathering.


But “a great deal” of spread occurs in households, Schaffner said, not places of business or congregate settings. Siegel, the civil engineer at the University of Toronto, said “everyone should be should be prepared” for when someone in their household gets infected. He added that one of the best ways to do so is to buy a portable HEPA filter.

He added that if someone in a household gets infected, it may be tempting to accept that the virus will spread throughout the house, but with enough space and commitment to precautions, that doesn’t need to be the case. The CDC recommends that Covid-19 patients isolate in their own bedroom and bathroom if possible to avoid infecting others in the house. And in common areas, the CDC says people should open windows and improve ventilation to reduce risk of infection.

Siegel said it would help to also place a portable HEPA filter in the room with the infected person to clean the air at the source. That won’t eliminate all risk, he said, but in conjunction with wearing a mask and frequent hand washing, it could go a long way.

“Filters and ventilation all play a role here, but fundamentally, I think of them more as kind of taking the edge off the risk once you’ve already done everything right to reduce it,” he said.

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