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.

How Blade Air's Pro Filter Technology Transforms Indoor Air Quality in Old Buildings

Jennifer Crowley
Jul 4, 2024
3 min read

Updated: Jul 8, 2024

Blade Air's Pro Filter halfway inserted into an HVAC system — Blade Air's Pro Filter technology offers a cutting-edge solution to enhance IAQ and energy efficiency in older buildings.

Maintaining optimal indoor air quality (IAQ) in old buildings presents a unique set of challenges. Over time, these structures accumulate dust, allergens, and pollutants that can compromise the health and well-being of occupants. Outdated HVAC systems often struggle to keep up with modern air quality standards, leading to inefficient energy use and increased operational costs. This is where Blade Air's Pro Filter technology comes in, offering a cutting-edge solution to enhance IAQ and energy efficiency in older buildings.

What is Pro Filter Technology?

Blade Air’s Pro Filter technology is a revolutionary advancement in air purification. Unlike traditional filters, the Pro Filter uses unique electromagnetic filtration to capture and neutralize airborne particles. This technology works by charging particles in the air, making them easier to capture. The result is superior filtration efficiency, improving indoor air quality by as much as 2.25x and capturing particles 40x smaller than standard filters.

Key Features and Benefits

1. Energy Savings:

One of the standout features of the Pro Filter is its ability to reduce energy consumption. Traditional HVAC systems often require significant energy to push air through dense filters. However, the Pro Filter's low-pressure drop design allows air to flow more freely, reducing the load on HVAC systems. This results in up to 75% reduction in fan motor savings.

2. Operational Efficiency:

The Pro Filter technology not only enhances air quality but also improves the overall operational efficiency of HVAC systems. With its advanced design, the Pro Filter requires less frequent maintenance and replacement compared to traditional filters. This leads to lower operational costs and less downtime, with savings as high as 50%, ensuring that buildings can maintain a consistent level of air quality with minimal interruption.

3. Superior Filtration Capabilities:

The Pro Filter’s unique electromagnetic filtration process is designed to capture even the smallest airborne particles. Our Pro Filters capture ultrafine particles including viruses and bacteria, far exceeding the capabilities of traditional pleated filters and ensuring the air in your building is clean and safe. This is particularly beneficial for occupants with allergies or respiratory conditions, as it significantly reduces the presence of allergens and other irritants.

4. Logistics Efficiency:

Streamlined logistics opportunities can significantly reduce storage needs and delivery requirements, potentially resulting in up to 92% cost savings while also lowering emissions.

Case Study: Pro Filter Technology in Old Buildings

Toronto's historic Distillery District — After retrofitting with Blade Air's Pro Filter technology, the district saw a 75% reduction in supply fan motor consumption.

Case Study - The Toronto Historic Gooderham & Worts Distillery District

The Toronto Historic Gooderham & Worts Distillery District, a collection of 47, 19th-century buildings in downtown Toronto, faced significant challenges with poor air quality and high energy costs due to its outdated HVAC system.

After retrofitting with Blade Air's Pro Filter technology, the district saw a 75% reduction in supply fan motor consumption and a 2.25x increase in filter performance compared to their previous MERV 13 solution. This upgrade effectively captured and removed bacteria from the airstream.

In addition to the substantial energy savings and reduced maintenance costs, the retrofit significantly improved indoor air quality, enhancing the overall environment for occupants. The improved air quality has even contributed to better cognitive function among the residents, all achieved with no added retrofit costs. The transformation highlights the benefits of modernizing air filtration systems in historic buildings.

Read the full case study or watch the video case study.

What Our Customers Are Saying

Jamie Goad, Co-Founder, Distillery District:

"We selected Blade Air after fairly exhaustive research...some of the things that were quite compelling were its ability to adapt to the kinds of HVAC systems we already have in place...distributed air handling, the ability to increase the level of filtration, the potential for energy saving, we wanted a product our own maintenance staff could replace...A number of important issues that were all satisfied by the Blade Air Product."

Russel Ross, Bayview Golf & Country Club:

"Wow, what a company. Great products, great prices and service. We put one [HEPA Air Purifier] into our club restaurant. What a difference! Air smells fresh and the members are really excited that the club is protecting them. Keep up the great work!”

Improving indoor air quality in old buildings doesn’t have to be a daunting task. Blade Air’s Pro Filter technology, particularly in old buildings, offers a proven solution that enhances IAQ, reduces energy consumption, and improves operational efficiency. If you're ready to transform your building’s air quality and enjoy the benefits of cutting-edge filtration technology, contact Blade Air today for a consultation and learn more about our retrofitting services.

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