Air Purifiers, Air Filters, and the Best DIY Hacks to Reduce the Coronavirus Risk
How to clear the air in your home to protect against airborne Covid-19 transmission

Efforts to prevent Covid-19 infections have focused largely beyond the home, emphasizing crowded indoor public spaces. But after our son attended an event where he could have been exposed to the coronavirus, and we were told it could take a week to get test results, I began a quest to understand what to do if someone brings the virus home without knowing they are infectious, and how to create a sustainable defense for the “just in case” scenario, amid so many uncertainties.

First question: What are the odds family members will get infected?

“It clearly happens,” says Ashish Jha, MD, a practicing internist and professor of medicine at Harvard Medical School. “The attack rates are nowhere near 100%, they’re maybe 15 to 20%.” In other words, on average across all households with an infected person, 15% to 20% of family members would get the disease. A review of 40 studies on the topic, published August 1 but not yet peer-reviewed by other scientists, put the figure at 18.8%. Of course, many factors can affect these odds, including how many people are living in a given home and how crowded it is.

Second question: How can we lower the risk?

Improving ventilation in your home and filtering out the airborne coronavirus particles lowers the risk of Covid-19 infections, experts agree. Solutions range from cheap do-it-yourself hacks to not-so-cheap filter upgrades for a whole-house heating or air conditioning system, to somewhat more expensive but surprisingly useful portable air cleaners. Some tactics are most useful when you know there’s a sick person at home. Others can be used continuously just in case — perhaps particularly wise with schools opening, given that we now know kids can be infected and highly infectious.

All the approaches can be seen as layers of prevention that, when added together, further reduce risk. As a bonus, these same techniques will help reduce the spread of a cold or the flu. Also, allergy sufferers may find significant relief when the indoor air is cleaner, and everyone can enjoy the removal of smells, be they from tobacco smoking or bacon frying. The basic principles can be employed in small offices and other buildings, too.

Feel free to skip down to the tactics. But to better understand the best strategy for your home and your budget, a crash course in how the virus gets around will prove helpful.
What you’re dealing with

The coronavirus is expelled in respiratory droplets when an infected person talks or just breathes, and more so if they sing or shout. Heavier, sometimes visible droplets fall to the ground, typically within about six feet. Smaller droplets, called aerosols, are mostly invisible and can waft through the air, like cigarette smoke or hairspray, carrying virus particles around a room and even through a forced-air heating or air conditioning system, studies show.

The coronavirus can remain viable in aerosols many minutes or possibly hours, research suggests. The risk is known to be much greater indoors, especially in poorly ventilated buildings, compared to outside.

Infection can occur when these particles are inhaled by another person or they otherwise get in the eyes, nose, or mouth. Surfaces can harbor the virus and cause infections, but the most common method is through the air, experts say, and they urge a layered approach to lowering risks — clearing or diluting indoor air, masking up, distancing, and disinfecting surfaces.

“I think it is possible in a house, if you don’t have proper filtration, to actually spread the virus.”

“There is definitely a risk of airborne transmission in a home, but at the moment, we do not know the importance of any particular transmission route,” says Linsey Marr, PhD, an expert in airborne transmission of viruses at Virginia Tech. “Given the evidence, it seems wise to take a precautionary approach and take measures to reduce the risk of transmission via respiratory droplets of all sizes, including those that can be inhaled, and contaminated objects.”

Several factors affect airborne infection risk, including:

Dispersion and dilution: Airborne virus particles become more diluted the farther they waft from the source and the more they mix with fresh air or pass through filters.
Dose and duration: Odds of infection increase with proximity to a source and time spent amid airborne virus particles. Exact thresholds are not known.
Breathing rate: Singing, shouting, or exercising all increase the number of viral particles exhaled by an infected person or inhaled by someone nearby.

A person who is exercising might expel or take in 20 times as many viral particles in a given time period as someone breathing normally, says Richard Corsi, PhD, an engineer at Portland State University who studies indoor air quality. “This is one of the reasons gyms are particularly risky environments.”

Back home, armed with that information, you’re ready to take a layered approach to the coronavirus capture and dispersion, with each of several tactics further reducing the risk of infection should someone bring the pandemic home.
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