The questions of when and how to reopen schools and other indoor spaces has shaken the country. National and local media coverage as well as viral social media posts tend to focus on potential virus spread through direct contact among people. For example, observers question how kids can be taught to maintain social distancing procedures while wearing masks, and teachers’ unions are considering “safety strikes.”
While masks and social distancing are paramount in preventing the spread in schools, many have overlooked a key factor that can determine whether these measures can be successful: ventilation, or how air moves through a building.
It is difficult to draw attention to the importance of ventilation, since it is something we don’t often think about (unless the office is drafty or a subway car’s AC is broken). Ventilation is especially concerning because the quality of air flow is often imperceptible. While we can see whether the people around us are wearing masks, we can’t see if the room we are in has effective ventilation. And this is unsettling. As reported by NPR, “The fact that aerosolized viral droplets can move in air currents…means that if you are in a room with an infected person and fresh air is not circulating, even if you are socially distancing to keep 6 feet apart at a minimum, you may not be safe.” 
Researchers across the globe are still working on understanding how exactly COVID-19 is transmitted and how proper ventilation can inhibit the spread. It is clear, however, that ventilation plays an important role. In a quote cited by NPR on August 15, Abraar Karan, a physician and global health researcher at Harvard Medical School, said “We didn’t focus on ventilation as much early on [in the pandemic] as we probably should have.” 
So if you are able to control the ventilation in your office or other indoor space, what should you check for, and what should you invest in? What questions should parents ask about their childrens’ schools’ HVAC (Heating, Ventilation, and Air Conditioning) systems? Understanding the details of an HVAC system can be daunting. Here are a few places to start.
WNYC has a short podcast in which host Brian Lehrer discusses common ventilation questions with Dr. Linsey Marr, the Charles P. Lunsford Professor of Civil and Environmental Engineering at Virginia Tech University. Dr. Marr answers questions from a teacher and a pastor, among others.
Recommendations include opening windows, installing or upgrading HVAC filters, installing a humidifier, and using air purifiers in rooms where the ventilation cannot be altered. HVAC filters are rated on the MERV (minimum efficient reporting value) scale. Upgrading to MERV 13 or higher (or the highest your HVAC system can handle) will remove the most viral particles. 
To better understand how air circulates, see this article from the New York Times, which animates the air circulation process in the city’s subway cars.
 Craig, J. (August 2020) Can Air Conditioners Spread COVID-19? From NPR https://www.npr.org/sections/goatsandsoda/2020/08/15/897147164/can-air-conditioners-spread-covid-19 Accessed August 18 2020
 Lehrer, B. (August 2020) Ventilation and COVID-19 from WNYC https://www.wnyc.org/story/ventilation-and-covid-19/ Accessed August 18 2020