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.

IAQ Excellence through Leadership: Promoting Indoor Air Quality in Organizations

Jennifer Crowley
Apr 1, 2024
3 min read

Updated: Jul 8, 2024

Business leader standing up and speaking to his attentive team in an open boardroom setting — Organizational Leaders can create a healthier and more supportive work environment through IAQ

As leaders, we understand the importance of fostering a healthy and productive work environment for our teams. One often-overlooked aspect of workplace well-being is indoor air quality (IAQ). Poor IAQ can negatively impact employee health, productivity, and overall satisfaction. Therefore, it is essential for organizational leaders to prioritize IAQ excellence and promote a culture of indoor environmental quality within their organizations. In this blog post, we will explore the role of leadership in advancing IAQ initiatives and share strategies for cultivating a healthier indoor environment for employees.

The Impact of Indoor Air Quality on Workplace Well-being:

Indoor air quality plays a significant role in shaping the overall indoor environment and the well-being of occupants. Poor IAQ can lead to a range of health issues, including respiratory problems, allergies, headaches, and fatigue, which can directly impact employee productivity and performance. Additionally, inadequate ventilation and indoor pollutants can contribute to discomfort, decreased concentration, and increased absenteeism among employees. By prioritizing IAQ excellence, leaders can create a healthier and more supportive work environment conducive to employee well-being and success.

The Role of Leadership in IAQ Excellence:

Setting Clear Priorities: As leaders, it is essential to prioritize IAQ excellence as a fundamental aspect of organizational health and safety. Communicate the importance of IAQ to all stakeholders and establish clear goals and objectives for improving indoor environmental quality within the organization.
Allocating Resources: Provide adequate resources, including budgetary allocations and personnel support, to implement IAQ initiatives effectively. Invest in advanced HVAC systems, air filtration technologies, and IAQ monitoring tools to ensure optimal indoor air quality levels.
Leading by Example: Demonstrate a commitment to IAQ excellence by incorporating indoor environmental quality considerations into organizational policies, practices, and decision-making processes. Lead by example by adhering to IAQ guidelines and promoting healthy indoor habits among employees.
Educating and Empowering Employees: Raise awareness about the importance of IAQ and provide training and educational resources to employees on maintaining healthy indoor environments. Empower employees to contribute to IAQ initiatives by encouraging open communication, feedback, and participation in indoor environmental quality programs.
Collaborating with Experts: Seek guidance from IAQ experts, environmental consultants, and HVAC professionals to assess indoor air quality conditions, identify potential IAQ issues, and implement effective solutions. Collaborate with interdisciplinary teams to develop comprehensive IAQ strategies tailored to the organization's unique needs and priorities.

Multi-racial group of employees walking through the office in conversation — Promote employee health and wellness initiatives that support IAQ excellence

Evangelizing IAQ from Within:

Encourage Open Communication: Foster a culture of transparency and open communication regarding IAQ concerns and initiatives. Encourage employees to report any IAQ-related issues or discomfort promptly and address concerns in a timely and responsive manner.
Implement IAQ Policies and Guidelines: Establish clear IAQ policies, guidelines, and best practices to ensure consistent indoor environmental quality standards across the organization. Communicate IAQ protocols and procedures to employees and provide guidance on maintaining healthy indoor habits.
Create Healthy Indoor Environments: Implement measures to improve indoor air quality, such as proper ventilation, air filtration, humidity control, and the use of low-emission building materials. Design workspaces with IAQ considerations in mind, incorporating natural ventilation, access to daylight, and greenery to enhance employee comfort and well-being.
Foster a Culture of Wellness: Promote employee health and wellness initiatives that support IAQ excellence, such as wellness programs, ergonomic assessments, and stress management resources. Encourage physical activity, healthy eating habits, and mindfulness practices to enhance overall well-being and resilience.
Monitor and Evaluate Performance: Regularly monitor and evaluate IAQ performance metrics to assess the effectiveness of implemented measures and identify areas for improvement. Conduct IAQ audits, air quality testing, and occupant surveys to gather feedback and ensure continuous IAQ excellence within the organization.

As organizational leaders, we have a responsibility to prioritize the health, safety, and well-being of our employees. By promoting a culture of IAQ excellence and investing in indoor environmental quality initiatives, we can create healthier, more productive work environments that support employee satisfaction, engagement, and success. Together, let us lead the way in championing IAQ excellence and fostering healthier indoor environments for all.

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