When used correctly, air and HVAC filters can help reduce airborne contaminants, including viruses, in a small building or space. By itself, cleaning or filtering the air is not enough to protect people from COVID-19.Leakage in building heating, ventilation and air conditioning (HVAC) systems may be part of a general risk mitigation approach, but it is generally not considered a solution on its own. It's important to note that most air conditioners recirculate air within a space, rather than drawing fresh air from outside like an open window would. While no portable air filtration system has been proven to filter COVID-19, research does support an air purifier's ability to filter common airborne viruses, provided that the system captures infected air.
Your first line of defense against overhead transmission, and perhaps the easiest to upgrade, is your home's air conditioning filter. When you close doors and windows to keep warm air out, you essentially eliminate the flow of fresh air so that everyone in the room breathes and breathes the same air again. We reached out to some HVAC experts, including members of the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) Epidemic Working Group, to learn their perspectives on the potential risks of different types of air conditioning systems, as well as the strategies they might have for people worried about staying cool and healthy this summer. After examining video footage of diners who were infected and simulating transmission of the virus, the scientists concluded that the small outbreak was caused by strong drafts from the air conditioning unit on diners, which was blowing aerosols containing the virus from an infected person to those close by.
For many years, homeowners have had the option of installing ultraviolet lights in their HVAC system, where the air that is distributed through the home is first treated inside sealed air ducts. In fact, other infectious diseases such as measles, tuberculosis, chickenpox, influenza, smallpox and SARS have been shown to spread through heating, ventilation and air conditioning systems. Research shows that changing the air in a room several times an hour with clean or filtered outdoor air (using a window fan, using higher MERV filters in a heating, ventilation and air conditioning (HVAC) system, using portable air cleaning devices, and even simply opening a window), can reduce the risk of transmission of COVID-19.Studies show that five air changes per hour reduce the risk of transmission by 50 percent. Kathleen Owen of Owen Air Filtration Consulting told us that in a large system that serves multiple rooms, there is often a way to filter at least some environmental particles.
In the home, the risk of contracting COVID-19 through drafts or air conditioning units is no more likely to spread the virus through close contact or touching contaminated surfaces. Experts agree that the most practical method for now is high-efficiency HEPA filtration of particulate air most commonly found in portable air purifiers.