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.

Why HEPA Filters Matter in Wildfire Season

Jennifer Crowley
Jun 28, 2024
4 min read

Updated: Jul 8, 2024

Firefighters working on a steep ravine to try and extinguish wildfires — As wildfire seasons become increasingly severe, HEPA filters play a crucial role in maintaining clean indoor air quality and protecting health.

As wildfire seasons grow longer and more intense, especially in regions like Canada and the western United States, maintaining clean indoor air quality has never been more important. At Blade Air, we understand the critical role that HEPA (High-Efficiency Particulate Air) filters play in protecting both residential and commercial indoor environments from the harmful effects of wildfire smoke. This guide explores why HEPA filters are essential during wildfire season and how they can make a significant difference in your air quality and overall health.

Hazy view of wildfire haze across a city scape as seen by two masked individuals on a balcony — The most harmful components of wildfire smoke are particulate matter (PM), since they can penetrate deep into the lungs, enter the bloodstream and lead to various health issues.

The Importance of Air Quality During Wildfire Season

Wildfire smoke is a complex mixture of gases and fine particles from burning vegetation, building materials, and other substances. The most harmful components of wildfire smoke are particulate matter (PM), especially PM2.5 (particles smaller than 2.5 micrometres). These microscopic particles can penetrate deep into the lungs and even enter the bloodstream, leading to various health issues:

Respiratory Problems: Persistent coughing, wheezing, and shortness of breath.
Aggravation of Asthma and COPD: Increased frequency and severity of attacks.
Cardiovascular Issues: Heart attacks and strokes.
Eye, Nose, and Throat Irritation: Immediate discomfort and potential long-term damage.
Long-term Health Impacts: Lung cancer and complications in vulnerable populations, such as children and pregnant women.

Understanding these risks underscores the critical need for effective air filtration during wildfire season. HEPA filters are designed to capture these dangerous particles, making them indispensable in safeguarding indoor air quality.

Blade Air HEPA Air Purifier — HEPA's superior performance lies in their ability to trap particles as small as 0.3 micrometres with at least 99.97% efficiency.

What is a HEPA Filter?

A HEPA filter is a type of mechanical air filter that forces air through a fine mesh, capturing harmful particles such as dust, pollen, smoke, and bacteria. To be classified as a true HEPA filter, it must meet stringent standards set by the United States Department of Energy (DOE) and effectively remove at least 99.97% of airborne particles as small as 0.3 micrometres (µm).

HEPA Filters: Essential in Wildfire Season

HEPA filters offer multiple benefits that are particularly crucial during wildfire season:

Superior Filtration Efficiency

HEPA filters are renowned for their ability to capture very fine particles, including those found in wildfire smoke. The key to their superior performance lies in their ability to trap particles that are as small as 0.3 micrometres with an efficiency rate of at least 99.97%. This ensures that even the smallest and most harmful particles are removed from the air:

Effective Against PM2.5: Given that PM2.5 is the most dangerous component of wildfire smoke, HEPA filters are highly effective in providing protection.
Captures a Range of Pollutants: In addition to smoke particles, HEPA filters also capture other pollutants such as pollen, dust mites, and pet dander.

Health Benefits

The health benefits of using HEPA filters during wildfire season are significant:

Reduces Respiratory Symptoms: People with allergies, asthma, and other respiratory conditions experience fewer symptoms.
Decreases Cardiovascular Risks: Lower exposure to airborne particles reduces the risk of heart attacks and strokes.
Improves Overall Well-being: Cleaner air contributes to better sleep, productivity, and mental clarity.

Reinforcing HEPA Filters with Activated Carbon

Many HEPA air purifiers also include activated carbon filters. While HEPA filters are designed to capture particles, activated carbon filters are effective at removing gases and odours such as volatile organic compounds (VOCs) that are released during wildfires. This combination of filters provides comprehensive air cleaning:

Odour Removal: Activated carbon filters eliminate the smoky smell associated with wildfires.
Chemical Filtration: They remove harmful chemicals such as benzene and formaldehyde.

How to Choose the Right HEPA Air Purifier

When selecting a HEPA air purifier, consider the following factors to ensure you are getting the most effective protection during wildfire season:

True HEPA Certification: Ensure the air purifier uses a true HEPA filter, meeting DOE standards for filtration efficiency.
Clean Air Delivery Rate (CADR): Look for a high CADR rating for smoke. This measures the air purifier’s efficiency in cleaning air.
Coverage Area: Match the air purifier’s coverage capacity (in square feet) to the size of your room or home area.
Filter Longevity and Ease of Replacement: Consider the lifespan of the filters and their ease and cost of replacement.
Noise Levels and Energy Efficiency: Choose a model that operates quietly and efficiently.

Using HEPA Filters: Best Practices

Illustrated image of an air purifier placed on a central location showcasing its air circulation capabilities — Strategic placement is important. Place the air purifier in the room where you spend the most time. For homes, this is often the bedroom or living room with a clear path for air to flow.

To maximize the effectiveness of HEPA air purifiers, follow these best practices:

Strategic Placement: Place the air purifier in the room where you spend the most time. For homes, this is often the bedroom or living room.
Continuous Operation: Keep the air purifier running 24/7 during wildfire season to maintain clean air.
Regular Maintenance: Replace HEPA and activated carbon filters according to the manufacturer’s recommendations to ensure optimal performance.
Seal Your Home: Use weatherstripping, door sweeps, and other measures to prevent outdoor air from entering your home. This reduces the burden on your air purifier.
Create a Clean Air Room: Designate a specific room with minimal outdoor air infiltration and use a high-efficiency air purifier to maintain air quality.

Blade Air: Your Partner for Clean Air

At Blade Air, we are dedicated to providing advanced air purification solutions that meet the highest standards of performance and reliability. Our flagship products, such as the HCFM-1 Portable HEPA Purifier, Pro Filter with Advanced Electromagnetic Filtration, and HEPA+ Filter, offer unmatched protection against wildfire smoke and other airborne contaminants.

Advantages of Blade Air HEPA Air Purifiers:

High-Efficiency Filtration: Our true HEPA filters effectively capture 99.99% of particles at 0.3 micrometres.
Comprehensive Coverage: Suitable for both residential and commercial spaces, providing wide-ranging protection.

As wildfire seasons become increasingly severe, HEPA filters play a crucial role in maintaining clean indoor air quality and protecting health. By investing in high-quality air purification systems and following best practices, you can significantly reduce exposure to harmful pollutants and ensure a healthier environment for yourself and your loved ones.

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