Flu Season Meets School Season: How Smarter Air Quality Keeps Classrooms Healthy

Every fall, classrooms fill with students—and viruses. Discover how smarter air quality strategies like low-resistance filtration, ventilation, and HEPA keep schools healthier, reduce absences, and support better learning outcomes.

Ava Montini

Aug 19, 2025

Written by

Published on

The scene every September

Every September, the school bell rings and hallways come alive again. But as backpacks and lunch boxes make their way back into classrooms, another unwelcome guest tends to sneak in too: flu season.

Teachers know it all too well. The cough that spreads from desk to desk, the hand sanitizer bottles running low by mid-morning, the spike in absenteeism that leaves lesson plans hanging. Parents know it when the inevitable call from the school office comes: “Your child has a fever, please come pick them up.”

It’s a cycle we’ve come to accept as part of the school year. But what if healthier air could help change that story?

Why flu season and school season collide

Respiratory viruses (including influenza) spread more readily indoors, where exhaled particles accumulate. That’s not speculative; CDC/NIOSH is unambiguous that better indoor ventilation reduces occupants’ overall exposure to airborne viruses. CDC

We also know influenza isn’t only about big droplets from a sneeze. People exhale infectious virus in fine aerosols during normal breathing and speaking, which can linger and travel within a room. That was demonstrated in a landmark study that detected infectious influenza virus in exhaled breath from symptomatic adults, no cough required. PNAS Nature

The drier, colder air from the fall and winter cause low humidity, helping influenza survive and transmit more efficiently. Put simply: when we bring students back into dry, tightly sealed buildings, small airborne particles build up and stay infectious longer. That’s the fixable part.

Think of clean classroom air as a budget with three line items:

Dilute what’s in the room (ventilation/outdoor air)
Remove what’s in the room (filtration/air cleaning)
Disable what’s in the room (UVGI where appropriate)

The key is using them together, sized to the space, and tuned to the school day.

What the standards now say and why it matters

Before the pandemic, most schools designed ventilation systems mainly for comfort—things like controlling odours or keeping CO₂ levels down—not for stopping the spread of illness.

That changed with ASHRAE’s new Standard 241, which focuses specifically on infection control. ASHRAE’s Standard 241: Control of Infectious Aerosols changes the target by introducing Equivalent Clean Airflow (ECA)—a flexible, additive way to hit a per-person clean air goal using any combination of ventilation, filtration, and proven air cleaning. That means a classroom can meet its target by mixing outdoor air with high-efficiency filters, HEPA units, and/or UVGI, rather than relying on outdoor air alone. ASHRAE+1

In parallel, CDC/NIOSH and EPA emphasize practical steps for schools: keep systems maintained, upgrade to MERV-13 or better where equipment allows, and supplement with portable HEPA when central systems can’t carry the whole load. CDC+1 Environmental Protection Agency

The evidence that this keeps kids in class

In a study of 162 California elementary school classrooms, illness-related absences dropped by 1.6% for every extra 1 l/s‑person of ventilation. Increasing ventilation to meet the state standard (7.1 l/s‑person) from the average (4 l/s‑person) could reduce absences by 3.4%, gain $33 million annually in attendance-based funding, while costing just $4 million more in energy.
A study across Washington and Idaho found that a 1,000 ppm increase in indoor CO₂ correlated with a 0.5–0.9% drop in average daily attendance, translating into a 10–20% rise in student absences.
In controlled environments, each 500 ppm rise in CO₂ resulted in 1.4–1.8% slower response times, along with a 2.1–2.4% lower throughput on cognitive tasks.
Harvard’s COGfx study revealed that building occupants in green-certified, well-ventilated environments scored, on average, 101% higher in cognitive tests than those in conventional buildings.

“Will MERV-13 break my units?” (The energy/airflow reality)

The honest answer: it depends on the filter you pick and your fan capacity. Research on rooftop units shows that moving from MERV-8 to MERV-13/14 can raise cooling-mode energy use by a few percent if the filter adds a lot of resistance, or it can reduce airflow if the fan can’t keep up. That’s why filter selection matters as much as efficiency.

Not all MERV-13 filters are created equal. Traditional pleated designs often create a higher pressure drop, forcing HVAC systems to work harder and sometimes leading to performance issues. But newer filtration technologies (explicitly engineered for low resistance at high efficiency, like Blade Air's Pro Filter,) are changing that equation. By combining advanced media with optimized form factors, these filters deliver MERV-13 (and higher) performance without the heavy airflow penalty.

California’s Title 24 research reinforces this point: Many modern low-pressure MERV-13 options can maintain pressure drops under 0.20 in. w.c., keeping systems within safe operating ranges. That means schools can improve air quality, meet public health guidance, and stay compliant without sacrificing system efficiency or longevity.

When you factor in the bigger picture—fewer student absences, better cognitive performance, and improved overall school operations—the ROI clearly tilts toward upgrading. Healthier air doesn’t just protect occupants; it protects the bottom line.

How this translates into a classroom target (the ECA idea)

ASHRAE 241’s Equivalent Clean Airflow lets you add up all the ways you’re cleaning air—outdoor air, central filtration, HEPA, UVGI—until you reach the per-occupant target for your space type. It’s flexible, measurable, and avoids unrealistic demands for 100% outdoor air in cold snaps. ASHRAE

A practical approach:

Estimate your current outdoor air (from design or testing).
Add the “clean air” from MERV-13 upgrades (using published efficiencies) and from each HEPA unit’s clean air delivery rate.
If the sum doesn’t meet the ECA target, add another portable unit or rethink your filtration strategy. ASHRAE

What about measurement and transparency?

CO₂ for ventilation

Track a few representative rooms across grade levels and building wings. Persistently high readings during class point to areas needing a fix (dampers, schedules, or supplemental air cleaning). Health Canada’s 1000 ppm residential benchmark is a useful anchor for conversations with families and staff. Canada.ca

PM₂.₅ for smoke days

A couple of low-drift sensors at kid-height in hallways or problem rooms can confirm your filtration strategy keeps indoor levels below outdoors during wildfire events. Health Canada and EPA both recommend this principle. Canada.ca

Bottom line

Flu season doesn’t have to mean higher absence rates and strained HVAC systems. The most effective path is a consistent program: keep ventilation tuned, use filters that balance efficiency with low resistance, and supplement with portable HEPA or UVGI where it makes sense.

Carbon Emissions 101: Breaking Down Embodied, Operational, and More

Ava Montini
Dec 11, 2024
5 min read

Updated: Dec 17, 2024

Carbon emissions touch every aspect of our lives—from the buildings we live into the devices we use. But, not all emissions are created equal.

While operational emissions from energy use often grab attention, the hidden impact of embodied carbon in materials is just as significant. In this blog, we’ll break down the difference between embodied and operational carbon and explore actionable ways to reduce emissions for a sustainable future.

What is Carbon and Why Does It Matter?

Carbon, in the context of climate change, refers to the greenhouse gases (GHGs) emitted into the atmosphere, primarily carbon dioxide (CO2). These emissions result from activities such as burning fossil fuels, deforestation, and industrial processes. GHGs trap heat in the atmosphere, contributing to global warming and its associated impacts, including rising sea levels, extreme weather events, and biodiversity loss. Humans emitted 36.8 billion metric tons of CO2 in 2022 alone, marking a new record for global emissions. A significant portion of these emissions stems from the energy sector, which accounts for 73% of global emissions, with electricity and heat production making up 42% of that share.

Deforestation and forest degradation account for approximately 11% of global carbon emissions annually. The loss of forests not only releases stored carbon but also reduces the planet’s ability to sequester new carbon. This dual impact underscores the urgent need for forest preservation and reforestation initiatives. To meet the Intergovernmental Panel on Climate Change (IPCC) goal of limiting global warming to 1.5°C, global CO2 emissions must decline by about 45% from 2010 levels by 2030 and reach net zero by 2050.

Reducing carbon emissions is essential to achieving global climate goals, such as the Paris Agreement's target of limiting global warming to 1.5°C. This requires a comprehensive understanding of the different categories of carbon emissions and how they interconnect, paving the way for effective mitigation strategies.

To better understand how carbon emissions are generated, let’s examine two key contributors: embodied and operational carbon.

Embodied Carbon

The Hidden Footprint

Embodied carbon refers to the CO2 emissions associated with the production, transportation, and construction of materials and goods. Unlike operational carbon, which occurs during the use phase of a product or building, embodied carbon is "locked in" from the start.

Lifecycle Stage

Embodied carbon includes emissions from raw material extraction, manufacturing, and supply chain logistics. It is typically fixed and cannot be reduced once the product is created.

Primary Sectors Affected

Construction, manufacturing, and technology production.

Why It Matters

Embodied carbon often represents a significant share of total emissions, especially in industries reliant on energy-intensive materials. The World Green Building Council reports that embodied carbon contributes up to 50% of a building’s total lifecycle emissions.

Skanska, a global construction firm, has implemented low-carbon concrete alternatives and tracked embodied carbon through digital tools to align with its net-zero goals.
Apple continues to prioritize energy efficiency by optimizing HVAC systems across its facilities. By implementing low-pressure HVAC filters and energy-efficient solutions, Apple reduces the energy required for ventilation, cutting operational carbon emissions. These upgrades contribute to Apple’s commitment to becoming carbon neutral across its entire value chain by 2030.

Actionable Steps

Use low-carbon materials such as recycled steel, bamboo, or cross-laminated timber.
Conduct lifecycle assessments (LCAs) to identify high-impact areas.
Foster partnerships with suppliers that prioritize sustainability.
Incorporate modular designs to reduce material waste and embodied carbon.

Operational Carbon

The Active Emissions

Operational carbon refers to the emissions generated during the use phase of a product or building. These emissions result primarily from energy consumption for heating, cooling, lighting, and operating machinery.

Lifecycle Stage

Operational carbon is ongoing and occurs throughout the usable life of a building, product, or system.

Energy Sources

Fossil fuels, grid electricity, and renewable energy significantly influence operational carbon levels.

Major Contributors

Commercial buildings, data centers, and transportation systems are key sources of operational carbon.

Why It Matters

Operational carbon is the dominant contributor to global emissions in many industries. The International Energy Agency (IEA) notes that buildings account for approximately 30% of global final energy consumption and 26% of global energy-related CO₂ emissions.

A substantial share of this energy use is attributed to heating and cooling systems. Specifically, space heating and cooling, along with hot water, are estimated to account for roughly half of global energy consumption in buildings. This highlights the significant impact of heating and cooling systems on building energy consumption and emissions.

The Empire State Building underwent a $550 million retrofit to improve energy efficiency, resulting in a 40% reduction in energy use and emissions.
Google's data centers have implemented AI-powered cooling systems developed by DeepMind, reducing cooling energy use by 40%.

Actionable Steps

Transition to renewable energy sources such as solar or wind power.
Implement energy-efficient appliances, HVAC systems, and LED lighting.
Leverage building management systems (BMS) to optimize energy use in real time.
Set energy benchmarks and continuously monitor performance.

Beyond Embodied and Operational Carbon: Other Key Terms

1. Carbon Offset

Refers to compensating for emissions by investing in projects that reduce or remove CO2 from the atmosphere, such as reforestation or renewable energy initiatives.

Delta Airlines invests in carbon offset programs, including reforestation projects in Kenya, as part of its commitment to becoming the first carbon-neutral airline.

2. Carbon Intensity

Measures the amount of CO2 emitted per unit of energy or production. This metric helps businesses evaluate and improve efficiency.

Tesla measures the carbon intensity of its manufacturing processes to ensure sustainability across its electric vehicle lifecycle.

3. Sequestered Carbon

Describes carbon captured and stored in natural or artificial reservoirs. Forests, soil, and biochar are examples of natural carbon sinks.

4. Scope 1, 2, and 3 Emissions (from the Greenhouse Gas Protocol)

Scope 1

Direct emissions from company-owned resources.

Scope 2

Indirect emissions from purchased energy.

Scope 3

Emissions from a company’s value chain, including suppliers and end-users.

Microsoft has pledged to become carbon-negative by 2030, aiming to reduce its Scope 1 and 2 emissions to near zero and cut its Scope 3 emissions by more than half.

Read more about Scope 1,2,3 reporting here

Strategies for a Holistic Carbon Reduction Plan

To create impactful carbon reduction strategies, organizations must address both embodied and operational carbon and then their broader carbon footprint.

Here are some tips:

Adopt Lifecycle Assessments (LCAs): Evaluate the total carbon impact of products or projects from cradle to grave.
Invest in Innovation: Support research and development for low-carbon technologies, such as carbon capture and storage (CCS).
Set Science-Based Targets: Align emission reduction goals with the latest climate science.
Engage Stakeholders: Collaborate with suppliers, customers, and employees to foster a culture of sustainability.
Leverage Digital Solutions: Use AI and IoT technologies to monitor and optimize energy usage, reducing operational carbon.
Adopt Circular Economy Practices: Design products for reuse and recycling to minimize waste and embodied carbon.

Embodied carbon reveals the hidden costs of our built environment, while operational carbon highlights ongoing emissions challenges. By taking a lifecycle approach and addressing emissions at every stage, we can pave the way for a sustainable, net-zero future.

And business leaders play a pivotal role in this transition. Prioritizing sustainability in supply chains, investing in renewable energy, and adopting innovative practices allows companies to drive change that benefits both the planet and their bottom line.

As awareness grows, the responsibility to act lies with every sector of society. From adopting renewable energy solutions to rethinking material choices, the path forward demands innovation, collaboration, and a commitment to reducing carbon footprints.

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