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Since the start of the pandemic, researchers have been trying to understand how COVID-19  spreads.

CDC guidance maintains that COVID-19 is primarily spread through large respiratory droplets produced when a person coughs or sneezes, but mounting scientific evidence suggests that even smaller virus particles can stay in the air and infect people as they inhale.

This risk of infection through these small particles is especially high in small enclosed spaces like your home, where the air is not being circulated as often while you may be in direct contact with others. 

Take a Look at Your Home’s A/C Filter

Your first line of defense against airborne transmission, and perhaps the easiest to upgrade, is your home’s air conditioning filter.

A  low-efficiency filter —less than MERV 8 according to ASHRAE Standard (American Society of Heating, Refrigerating and Air-Conditioning Engineers) is very unlikely to make a difference.

Minimum Efficiency Reporting Values, or MERV ratings, range from one to 16, with 16 being the best, filtering out 75% or more of the smaller particulate matter ranging from 0.3 to 10 microns. 

Scientists have found that respiratory droplets that could potentially spread COVID-19 range from 0.5 microns up to 15 microns, with the peak distribution size around 2.5 microns.

The EPA also recommends running your system fan in longer intervals, or continuously, because heating, ventilation and air conditioning systems filter the air only when the fan is running. Many systems can be set to run the fan even when no heating or cooling is taking place.

“Air filtration and increasing air changes per hour are a general air health recommendation,” said Stacy Martin, R.N., manager of the Infection Prevention and Control Department at Moffitt Cancer Center. “At this time, the jury is still out on whether additional air filters can prevent the spread of COVID-19.”

“Increased air exchange is important, though opening windows during the summer in Florida is probably not possible,” said Dr. Michael Teng, associate professor of molecular medicine and associate dean of internal medicine at the University of South Florida Morsani College of Medicine. “Keep the relative humidity between 40 to 60%. Ceiling fans can be helpful too.”

Michael Teng, PhD

USF Health virologist Michael Teng, PhD, studies how viruses work and has conducted NIH-supported research working toward a safe and effective vaccine for respiratory syncytial virus. Photo courtesy of USF Health.

Bottom line, make sure your filters have a MERV-A rating and have the highest filtration level possible that your A/C system allows.

Combine with UV Light

For many years, homeowners have had the option of installing ultraviolet lights in their HVAC system, where air distributed though the home is first treated inside sealed air ducts.

When administered in the correct amount, UV radiation alters the molecules of many viruses and germs so they are no longer infectious. A short burst of this light can disinfect large areas quickly.

While most home UV sanitizers have not been tested against COVID-19, UV light has been shown to kill related coronaviruses. Commercial applications of UVC light are being used to disinfect unoccupied spaces such as large stores, empty hospital rooms and even empty subway cars. However, the impact to humans through direct or side effects is unknown. Teng, an expert in virology, advises UVC will inactivate SARS-CoV-2, the virus that causes COVID-19.

Added Protection

Experts agree that the most practical method, for now, is high efficiency particulate air HEPA filtration most often found in portable air purifiers. HEPA filters, according to the EPA, can remove at least 99.97% of particles as small as 0.3 microns, or roughly the size of the COVID-19 virus.

While no portable air filtration system has been proved to filter out COVID-19, there is research supporting an air purifier’s ability to filter common airborne viruses, as long as the infected air is captured by the system.

What’s less clear is whether a HEPA purifier could catch the virus prior to the point of infection or what level of exposure to the virus even causes an infection. 

Experts Say It’s Better Than Nothing but...

Added air filtration methods may not necessarily protect you from the virus. The CDC says the coronavirus is primarily transmitted by person-to-person contact and that community spread can occur even when taking a reasonable level of precaution. 

“Enhanced air filtration will help,” said Teng. “However, unless you get to MERV-13, air filtration isn’t going to target the majority of particles the size of aerosolized virus. You’ll still need to practice good hand hygiene and surface disinfection. In the end, you’re more likely to get infected when outside of the house (work, shopping, etc.) than while at home.”