School Air Filtration and Ventilation Strategies To Improve Health, Education, Equity, and Environmental Outcomes

In late February 2020, the United States saw its first COVID-19-related school closure—and in just a matter of weeks, almost all the nation’s public schools had closed in response to the pandemic. Most remained closed through the end of the school year.¹ School closures have led to increased inequities as well as reduced access to school-based health care services, mental health repercussions, reductions in services for children with disabilities, lower lifetime earnings, and more.² In short, school closures have had a profound impact on education, health, the economy, and community life.

The COVID-19 pandemic has underscored the value of in-person learning, which requires investments in repairs and improvements to school infrastructure, particularly in disadvantaged communities, so that students are safe, healthy, and able to learn and so that schools are prepared for future threats. According to guidance and recommendations from more than 50 leading science and policy experts in a “Roadmap for Living with COVID,” “During an infectious disease outbreak, schools should be the last to close and the first to reopen.”³ This is not to say that in-person schooling is entirely risk free; the past two years have illustrated various risks associated with reopening schools. But research suggests that these risks can be managed.⁴

Key to managing the risk of infectious diseases such as COVID-19 is improving air quality. While improving air quality in schools has many benefits, the most immediate benefit is limiting the spread of the coronavirus so that schools can remain open. Another significant benefit is reducing the spread of common airborne respiratory illnesses such as colds and flu; during the 2018-19 school year, schools were forced to shut down due to flu-related illness among students and staff. Other benefits include better preparing schools for future outbreaks of novel airborne diseases; reducing allergens in the air that trigger respiratory illnesses such as asthma, which is one of the leading causes of school absenteeism; lessening inhalation of harmful respiratory particulates such as smog; and reducing other indoor air pollutants that are common in schools such as mold, dust, carbon dioxide, and carbon monoxide.⁵ By reducing illness, improving indoor air quality can reduce absenteeism and health care costs and enhance academic success.⁶ For example, children in classrooms with good indoor air quality tend to have higher scores on math and reading standardized tests.⁷ One study showed that academic performance improved 8 percent after schools’ ventilation rate was doubled from about 7.5 cubic feet per minute per person (cfm/person) to 15 cfm/person.⁸ Another study showed that every 2 cfm/person increase in the ventilation rate from 2 cfm/person to 15 cfm/person led to a 3 percent increase in the proportion of fifth-grade students who passed standardized math and reading tests.⁹

This report describes a range of strategies available to meet the urgent need to improve indoor air quality in schools and highlights the historic investment of federal funding and technical assistance currently available through the American Rescue Plan (ARP) and the Elementary and Secondary Schools Emergency Relief (ESSER I,II,III) Fund that state and community leaders can leverage to address a host of school-related issues. The report calls for leaders to use this opportunity to improve energy efficiency, decarbonize public schools, and ensure that resources reach vulnerable and disadvantaged communities. Finally, the report offers a slate of recommendations to improve health, education, and environmental outcomes through strategies that improve school air filtration and ventilation:

• Deliver long-term, dedicated federal funding to improve school facilities.
• Include schools as an ongoing and critical component of federal infrastructure investments.
• Prioritize funding to support filtration and ventilation system updates in socially vulnerable communities.
• Invest in research on ventilation levels and strategies that reduce disease transmission.
• Ensure all money dedicated to heating, ventilation, and air conditioning (HVAC) system upgrades and installations goes toward transitioning schools to carbon-free alternatives such as electric heat pumps, rather than locking schools into continued reliance on fossil fuels.
• Direct the U.S. Department of Education to report on school conditions, including indoor air quality, ventilation and filtration, and resources needed to guarantee sufficient conditions.

Improving the indoor air quality of schools is key to keeping schools open; ensuring students, teachers, and staff are healthy; and avoiding the trauma and the economic and education disruptions that have resulted from the lost in-person instructional time.

Among the available mitigation measures are strategies that clean the air to reduce virus-containing particles and the risk of spreading disease.¹⁰ Improving ventilation and air filtration is an evidence-based, institutional-level strategy for reducing the likelihood of spreading disease and has been found to be effective in schools.¹¹ Such strategies are considered part of a layered approach to COVID-19 prevention, which includes both personal behavioral interventions as well as interventions that alter the environment.¹² Upgrades of this sort can be appealing because they do not require individuals to change their daily behavior. Layered, or so-called Swiss cheese, approaches acknowledge that each layer of protection has holes but that combined, the layers block the holes and prevent disease.¹³

There are a variety of tools that can reduce contaminants in the air, lowering the risk of disease.¹⁶ In addition to measures such as social distancing, wearing masks, and vaccination, the Centers for Disease Control and Prevention (CDC) offers several ways schools can improve classroom ventilation. The Environmental Protection Agency (EPA) and the CDC have provided guidance for improving ventilation and air filtration and for estimating the impact of various interventions.¹⁷ Strategies range in cost and include:

• Opening windows to increase outdoor airflow.
• Using portable high-efficiency particulate air (HEPA) fan and filtration systems.
• Ensuring HVAC systems operate correctly and provide acceptable indoor air quality.

Comprehensive school renovations and improvements are ideal for addressing COVID-19 and have a host of other benefits for education, health, and the environment. However, schools and local policymakers can also make other improvised updates to improve ventilation and air filtration.¹⁸ Some improvements to indoor air quality, such as opening windows and using window fans, cost less than $100. Portable HEPA filters cost approximately $500 each.¹⁹

Such low-cost strategies bring in outdoor air, improve ventilation, and reduce COVID-19 risk.²⁰ A 2020 survey of schools in Georgia found that a variety of strategies to improve ventilation were associated with a lower incidence of COVID-19 cases.²¹ Although the incidence of COVID-19 was lower for schools that used both air filtration and ventilation strategies, those that used only ventilation strategies also showed reduced incidence of disease, indicating that simple low-cost strategies can be effective. In fact, one study found that fully opening classroom windows all day in winter resulted in a 14-fold reduction in COVID-19 transmission. Effectiveness varied depending on the season, the number of windows, and other factors.²²

Although opening windows may be a useful low-cost strategy when other options are not available, schools may need to balance this approach with other safety, health, and environmental concerns. Opening windows in schools that are located in communities with poor air quality and in classrooms with windows near idling diesel buses or other vehicles can significantly worsen air quality and pose serious health and academic risks to children inside schools.²³ In addition to some classrooms having windows that cannot be opened or no windows at all, opening windows poses a potential safety concern on lower floors, as people could use them to enter or exit the school building. Finally, allowing the exit of warm air in the winter and cool air in the summer through open windows wastes energy, counteracting the goal of improving energy efficiency described in the following section. Given these concerns, opening windows may be a short-term solution in the absence of available funding for more favorable approaches.

Nevertheless, these strategies can complement more sustainable and effective approaches such as using air cleaners that filter pollutants and remove contaminants, including COVID-19, from the air through HVAC systems; HEPA filters; and, when ventilation options are limited, ultraviolet germicidal irradiation.²⁴ A CDC simulation found that portable HEPA filters can reduce exposure to simulated coronavirus aerosols by up to 65 percent—and up to 90 percent when combined with universal masking.²⁵ A study in Italy that focused on school ventilation found decreased COVID-19 risk as ventilation quality increased, with up to an 82 percent reduction in risk for a system that provides six air changes per hour.²⁶ Upgrading HVAC systems is one way that schools can improve indoor air quality, ventilation, and air filtration to reduce the transmission of COVID-19 and other pathogens when students are in school.

There is an urgency and opportunity to weatherize and improve energy efficiency while decarbonizing public schools as part of school indoor air improvements. In addition to delivering critical public health and learning benefits to students, upgrading HVAC systems is one of the best ways that schools can weatherize, improve their energy efficiency, and lower utility bills. Extreme weather events—heat waves, cold snaps, wildfires, and more—are expected to increase in frequency and severity due to climate change, and many schools are not equipped with the HVAC systems they need to adapt adequately.

Those that do have serviceable HVAC systems will have to rely on them more and more, which can quickly drive up their energy bills. Energy is one of the leading expenses for K-12 public school districts, second only to teacher salaries, at more than $8 billion annually.²⁷ By installing efficient electric HVAC systems, as well as making other energy improvements, schools can save anywhere from 10 percent to 30 percent of their current energy bills and redirect these savings to resources that support student success and well-being, such as textbooks, computers, and additional staff.²⁸

The energy savings that schools stand to realize by upgrading their HVAC systems will vary in part by the nature of the HVAC equipment being replaced and what is replacing it. The energy use of electric air conditioning systems, for example, is up to 50 percent lower in new, more efficient models. HVAC is also only one part of the equation.²⁹ The physical infrastructure and insulation of a school building—in other words, the building envelope—is critical too: Even the most efficient HVAC system will waste energy if there is a hole in the classroom ceiling.

There is similar variability in the climate or emissions reduction benefits that schools can realize by upgrading HVAC systems. The building stock in the United States currently contributes about 12.5 percent of the country’s total greenhouse gas emissions per year through the direct use of fossil fuels, including for heating and cooling;³⁰ schools make up a portion of these emissions and will need to be fully electrified over the next three decades if the United States is to achieve its science-based climate goal of a net-zero emissions economy by 2050.³¹

Right now, most of the HVAC systems in school buildings comprise air-conditioning units powered by electricity to cool classrooms and furnaces or boilers powered by natural gas to heat them. So long as schools use fossil fuel-powered HVAC systems, they will be reliant on the burning of fossil fuels, exacerbating the very air pollution and climate change impacts from which they are trying to protect students. One study of the eastern United States found that without clean energy and energy efficiency interventions, climate change and increased energy demand could worsen air pollution from fine particulate matter (PM2.5) by about 60 percent, and from ground-level smog by about 16 percent, above current levels.³² The additional use of air conditioning, specifically, would be responsible for 4 percent of the increase in PM2.5 and 7 percent of the increase in smog, assuming energy demands are met using today’s mix of generation sources.³³ Furnaces and boilers also have relatively long life cycles of 10 years to 20 years, so when a school upgrades its HVAC system by installing a new gas-powered boiler or furnace rather than transitioning to an electric technology, it is effectively postponing electrification for another one to two decades.³⁴

One way that public schools can fully electrify their HVAC systems is through replacing their air conditioning units and gas-fired furnaces or boilers with heat pumps. Heat pumps work by transferring heat between the air inside the building and the air or ground outside the building. An increasing number of schools are transitioning to heat pumps for heating and cooling their facilities, but to date, they have typically been installed as one part of a larger school renovation.³⁵ This is because as a newer technology (especially for nonresidential buildings), heat pumps can have relatively higher upfront costs than conventional HVAC systems, a difference that can be cost prohibitive for schools in low- and middle-income communities.³⁶ However, once installed, heat pumps require considerably less energy to operate and can quickly pay for themselves through lower monthly utility bills.³⁷ To optimize the energy savings of schools while ensuring that they are not left behind in the transition to a 100 percent clean energy economy, federal and state support must be directed toward making heat pumps more-affordable and readily accessible alternatives to gas-fired HVAC systems.

Even before COVID-19 highlighted the need to improve school air quality, a Government Accountability Office (GAO) report based on a national survey of school districts from August 2019 to October 2019 found that “an estimated 41 percent of districts need to update or replace heating, ventilation, and air conditioning (HVAC) systems in at least half of their schools.”³⁸ HVAC systems were reported to be the building system or feature in greatest need of replacement. Failure to update these systems can lead to air quality issues, mold, and school closures during episodes of extreme heat.³⁹

The urgent call to upgrade these critical systems has been met with historic funding through the American Rescue Plan, which provided $122 billion for the Elementary and Secondary Schools Emergency Relief (ESSER III) Fund, in addition to the approximately $68 billion in ESSER I and II funds that Congress provided.⁴⁰ ARP funds can be used in schools to purchase high-efficiency particulate air filters, repair windows, upgrade HVAC systems to be consistent with industry standards, secure filters with a MERV of 13, and conduct testing and maintenance of systems.⁴¹ A recent analysis of the ARP spending plans of 5,004 school districts—representing 74 percent of public school students and almost 70 percent of the $122 billion provided through ESSER III funding—shows that about half the districts in the sample plan to improve their HVAC systems.⁴² It is anticipated that almost one-quarter of all ARP spending—nearly $26 billion—will be spent on school infrastructure upgrades, with the majority of expenditures going toward improving HVAC systems.

In addition to ESSER funds, the bipartisan Infrastructure Investment and Jobs Act (IIJA) provides an additional $500 million in grants for schools to install energy efficient HVAC, ventilation, renewable energy, and alternative fuel vehicle infrastructure improvements.⁴³ The Inflation Reduction Act of 2022 provides an additional $50 million to address air pollution in schools, most of which is designated for schools in low-income and disadvantaged communities.⁴⁴ Another bill currently in the House of Representatives, the Reopen and Rebuild America’s Schools Act of 2021, would provide an additional $100 billion in grants and $30 billion in bond authority targeted at improving facilities in high-poverty schools.⁴⁵ The Biden administration is also providing technical assistance to facilitate improvements. The Efficient and Healthy Schools campaign, an interagency effort of the Department of Energy, the Environmental Protection Agency, and the Department of Education, supports school districts in implementing indoor air quality and efficiency improvements to reduce energy use and improve health.⁴⁶ In addition, a Biden administration back-to-school fact sheet provides guidance and supports for schools, including plans to recognize leading school districts in their efforts to improve indoor air quality.⁴⁷

State and local policymakers, school systems, and voters are taking action to create programs and set priorities to improve school ventilation and air filtration using ARP funding. Efforts include installing indoor air quality sensors in Boston’s classrooms to identify areas of need; installing self-made air filters made from box fans in Monterey, California, classrooms (see text box); purchasing energy efficient unit ventilators in Camden, New Jersey; and establishing school indoor air quality grant programs for HVAC systems in Connecticut and Vermont.⁴⁸

Some school districts have been able to utilize ARP funding to complete large-scale projects to improve air quality across several schools within their districts. Charleston County School District in South Carolina budgeted more than $20.3 million of its total $163 million in ARP funding toward HVAC replacement and building envelope repair projects to improve air quality in its schools.⁵⁰ Denver Public Schools completed projects to improve air quality and ventilation using funding from the ARP to address concerns regarding the spread of coronavirus in schools. In addition to the $4.9 million that Denver Public Schools spent on HVAC upgrades during summer 2020, the district plans to spend $25 million of ARP funding—received throughout the school year and ending in 2024—on ventilation improvements that further improve indoor air quality.⁵¹ These improvements include making repairs, installing digital controls, and replacing air filters to allow HVAC systems to run more efficiently.⁵²

Greene County School District is a smaller, less-resourced district in rural Tennessee that invested $8.9 million in bonds to replace HVAC systems in schools across the district. At the time of the decision to go forward with the upgrades, almost half of the HVAC systems in the district had surpassed their 20-year life expectancy, and within a couple years, 85 percent of them would have been due for replacement.⁵³ The county commission approved the funding needed to upgrade the HVAC systems, which is projected to save the district more than $5 million in energy savings over 20 years, as well as provide students with better learning environments.

A Saint Paul, Minnesota, high school is going further by installing a ground-source geothermal heat pump system to provide for the school’s heating, ventilation, and air conditioning needs.⁵⁴ The project required a budget of $18.8 million and is scheduled for completion by the end of this summer. The district’s decision to invest in the geothermal heat pump option comes at a time when the effects of climate change are increasingly visible. Air conditioning is becoming essential in schools for a comfortable and safe learning environment as extreme heat becomes more prevalent. Heat pumps are an option for schools upgrading their HVAC systems; as stated above, they allow energy efficient heating and cooling without relying on fossil fuels. For schools that have the resources, heat pumps are the best option to fully decarbonize HVAC systems, as they cut air pollution and save on energy costs in the long run.

Funding must reach vulnerable and disadvantaged communities

On the first day of his presidency, President Joe Biden signed the “Executive Order On Advancing Racial Equity and Support for Underserved Communities Through the Federal Government.”⁵⁵ President Biden also established the Justice40 Initiative, a historic commitment to deliver at least 40 percent of the overall benefits from federal investments in climate and clean energy to disadvantaged communities.⁵⁶ These early actions serve as a clear sign directing federal agencies to take deliberate steps to enact policies that advance equity and provide resources to communities of color and other marginalized communities that need them most. Education Secretary Miguel Cardona echoed this commitment in a recent letter urging schools to “lead with equity and inclusion to ensure all students have access to in-person learning.”⁵⁷

Public schools receive the bulk of their funding from local and state government sources, with local taxes being the primary funding source to upgrade school facilities.⁵⁸ Since majority-nonwhite districts generate less funding from local property taxes, they must rely more on state funds to cover both day-to-day operations—including student services, classroom materials, and teacher salaries—and infrastructure upgrades.⁵⁹ In addition to lower levels of local tax funding, a 2019 report found that districts serving a majority of nonwhite students receive $23 billion less in total funding than districts serving a majority of white students.⁶⁰

According to the CDC’s National School COVID-19 Prevention Study of K-12 public schools from February 2022 to March 2022, schools most frequently reported using lower-cost strategies to improve air quality.⁶¹ Fewer schools reported replacing or upgrading HVAC systems or using HEPA filtration systems. Most U.S. public schools have not made major investments in improving indoor ventilation and filtration, and the use of several “resource-intensive strategies” was less common among rural schools and schools at the mid-poverty level. These findings reinforce the need to target federal funding to disadvantaged communities, in alignment with the Justice40 Initiative. Given that people of color and low-income communities are more likely to be exposed to air pollution,⁶² failure to target funding may leave communities that have fewer resources reliant on lower-cost strategies to improve air quality. These are the same communities that are disproportionately affected by extreme heat and COVID-19, meaning that targeting funding would reinforce the various benefits of having efficient HVAC systems.⁶³

Federal investments still fall short

Despite the historic federal investment in K-12 education, current funding mechanisms, including the ARP, ESSER, and IIJA, fall short of infrastructure needs across the country. These funding streams are not dedicated to improving school infrastructure and do not meet the $85 billion annual K-12 infrastructure spending gap, the $100 billion President Biden called for in his American Jobs Plan, or the estimated $1.1 trillion needed to upgrade and replace school buildings and systems in need over the next decade.⁶⁴ To provide all students with healthy, safe, and resilient learning environments, the federal government must deliver long-term dedicated funding to improve school facilities.

Given the unequal funding and ability of all schools to afford necessary facilities upgrades, federal, state, and local agencies must center equity as they allocate funds and services. By following the president’s order to lead with equity and inclusion, decision-makers can ensure these healthy school strategies reach districts with the most need and ensure all students have continued access to in-person learning.

The education disruption that COVID-19 caused underscores the need to improve the air quality inside schools to prevent illness, disease, and further lost instructional time. The following recommendations highlight opportunities to ensure improvements are effective, sustainable, and equitable.

Deliver long-term, dedicated federal funding to improve school facilities

Investments in all schools, with particular focus on those most in need, is critical to keeping schools open and ensuring equitable access to healthy, safe, and resilient learning environments, including ensuring clean air in every classroom. Although recent federal investments are significant, they cannot account for the vast need, nor can HVAC systems be installed in outdated and dilapidated buildings.⁶⁵ School infrastructure needs could consume all the available ARP funding before other significant issues are addressed.

Include schools as an ongoing and critical component of federal infrastructure investments

K-12 public school facilities are the second-largest sector of the country’s infrastructure, yet the federal government provides only 0.2 percent of school capital costs.⁶⁶ The remainder is provided by state and local governments and is contingent on property taxes, resulting in an inequitable system in which low-income communities are often unable to support improvements in their schools.⁶⁷ Schools must be included in federal infrastructure improvement plans.

Prioritize funding to support filtration and ventilation system updates in socially vulnerable communities⁶⁸

Closing schools for long periods of time during the COVID-19 pandemic had a profound effect on students, even more so in majority-Black and low-income schools.⁶⁹ While resources are available to improve school ventilation and air filtration, they must be equitably distributed and used to improve schools most in need.

Invest in research on ventilation levels and strategies that reduce disease transmission

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) sets indoor air quality standards based on the number of air changes needed per hour to ensure clean air, and has issued general guidelines for reducing exposure to the coronavirus.⁷⁰ ASHRAE standards often translate into local building codes, but they often do not apply to older buildings. More detailed studies on the relationship between ventilation levels and disease transmission could inform new indoor air quality standards and could be used to establish strong federal standards for indoor air quality, which currently do not exist.⁷¹

Ensure all money dedicated to HVAC system upgrades and installations goes toward transitioning schools to carbon-free alternatives

The provision of federal funding for the improvement of school facilities must not come at the expense of locking schools into continued reliance on fossil fuels. Equally, schools cannot be expected to fully decarbonize their HVAC systems by 2050 without the know-how and financial means to do so. Provisions enacted through the Inflation Reduction Act of 2022—including manufacturing tax incentives and consumer rebates for residential heat pumps—will support heat pump production and, in turn, may lower the upfront costs of heat pump equipment and installation in nonresidential settings.⁷² As consumers take advantage of these provisions to transition to heat pumps within their homes, the Department of Education, the Department of Energy, and state energy offices must provide school facilities with the technical guidance and financial tools they need to realize the benefits of heat pump proliferation, ensuring their installation over fossil fuel-powered HVAC alternatives.

Direct the Department of Education to report on school conditions

The Reopen and Rebuild America’s Schools Act of 2021 calls for states to track public school facility conditions. A federal survey of K-12 school infrastructure would gather information to support needed investments.⁷³ Along these lines, as part of the president’s fiscal year 2023 budget request, the Department of Education proposed a new Office of Infrastructure and Sustainability to support schools in creating “healthy, safe, sustainable 21st century learning environments.”⁷⁴

The COVID-19 pandemic has highlighted the importance of clean indoor air to create conditions for good health, learning, and development in schools. With new coronavirus variants emerging, coupled with other respiratory and chronic conditions that impede learning, now is the time to take advantage of unprecedented federal support and funding to upgrade school ventilation and air filtration systems. Federal, state, and local leaders should dedicate and expand resources to support upgrades and improvements that promote school weatherization, decarbonization, and energy efficiency, while addressing the inequities that have disproportionately affected majority-Black and low-income schools.

The authors would like to thank the Center for American Progress’ Domestic Climate, K-12 Education Policy, and Health teams for their input and guidance and the CAP Editorial team for its valuable contributions to this report.