Getting kids back to in-person learning could hinge on upgrading the ventilation systems in school buildings.

Why it matters: This is a massive undertaking in the U.S., where school maintenance has been neglected and the average school building is 44 years old. Significant stimulus funds can be funneled to installing new A/C systems, but it may not happen by fall.

How it works: Scientists now realize that poorly ventilated settings increase the likelihood of airborne transmission of COVID-19.

• The concentration of viral particles in the air is usually higher indoors than outdoors, where a breeze can quickly reduce the particle concentration, per the CDC. Better indoor ventilation means it's less likely that viral particles are inhaled or contact eyes, nose and mouth, or fall onto surfaces.
• While the CDC says it's not necessary, in most cases, to install new ventilation systems to re-occupy a building during the pandemic, its guidance to school districts seeking to reopen is to ensure ventilation systems operate properly.

Where it stands: 4 in 10 U.S. school districts need to update or replace the HVAC systems in at least half of their school buildings — affecting about 36,000 school buildings, according to a June 2020 Government Accountability Office report.

• At a school in Rhode Island, some components of its HVAC system are nearly 100 years old. A Michigan school is heating the building using a boiler from the 1920s, per the report.
• Some school buildings that remained open this year tried to increase air flow by opening windows to incorporate outside air and used fans to keep air circulating. This is hard to do on very hot or cold days, though.

What's happening: The $1.9 trillion COVID-19 relief package includes $168 billion for K-12 schools and colleges. School districts have until 2024 to use the money.

• Rep. Bobby Scott, (D-Va.) — Chairman of the House Education and Labor Committee, who's been focused on measures to safely open schools — said schools have not been maintained properly. Many, particularly those serving low-income students and communities of color, need a lot of renovation.
• Some estimates put the cost of bringing America's schools up to code at $200 billion.
• Scott introduced the Reopen and Rebuild America's Schools Act of 2021, which would invest $130 billion in physical and digital infrastructure. That proposal is mentioned as part of President Biden's $3 trillion infrastructure propsal.
• That funding "will get us well on the way to addressing the deficits in school infrastructure, the school buildings, internet connections, ventilation systems, and everything else schools need," he said during an Axios virtual event last week.

What to watch: Upgrading schools' HVAC systems may also have other benefits for students beyond COVID-19. Studies have also linked better ventilation to increases in productivity, morale and even cognitive function, Axios' Marisa Fernandez reports.

• Even a 2-4% increase in productivity can lead to financial gains, William Bahnfleth, professor of architectural engineering at Pennsylvania State University, told Axios.

Reality check: Improved ventilation alone is not the silver bullet for safely reopening schools. It's part of a "layered approach" that also includes wearing masks and keeping children socially distanced.