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.

Electrostatic Air Filter vs. HEPA: Which One Should You Choose?

Jennifer Crowley
Jul 31, 2023
3 min read

Updated: Jul 9, 2024

An electrostatic filter sits beside a HEPA filter — Electrostatic Air Filter and HEPA technologies have their pros and cons let's explore their differences to help you make an informed decision on which will work best for your business..

When it comes to air filtration, there are two popular options; the Electrostatic Air Filter vs. HEPA. Both technologies have their pros and cons, and choosing between them can be confusing. In this blog, we’ll compare electrostatic air filters and HEPA filters to explore their differences to help you make an informed decision.

What are Electrostatic Air Filters?

The main idea of electrostatic filters is to utilize static electricity to attract and trap particles on the charged fibres and carbon paths. So instead of getting pulled through and being blocked by filter material like standard filters, the particles are attracted to the filter media.

Comparison chart of ionized vs. polarized technology — Let's compare Ionized vs. Polarized technology side by side.

You will encounter two standard electrostatic technologies when searching the different types of electrostatic filters. In this article, we will be comparing the two:

Electrostatic Ionized Technology
Electrostatic Polarized Technology

Unlike the more common ionizing technology found in most electrostatic air filters, polarized-media air cleaners do an exceptional job of removing sub-micron (<1 micron in size) particles without the efficiency loss associated with precipitating electronic air cleaners. In addition, as each particle attaches itself to the fibre strands, it, in turn, becomes part of the collection process, thereby increasing the effectiveness of the filter as it loads. Polarized media also produces no ozone – making the filter better, not only in performance but for our health.

Pros of Electrostatic Polarized Air Filters:

Polarized-media air cleaners do an exceptional job of removing sub-micron (<1 micron in size) particles without the efficiency loss associated with precipitating electronic air cleaners
Increase HVAC system efficiency
They’re relatively inexpensive compared to HEPA filters.

What are HEPA Filters?

HEPA filters are made of tightly woven fibres that trap airborne particles as air passes through. They’re designed to capture particles as small as 0.3 microns, including dust, pollen, pet dander, and even viruses.

HEPA filters are designed to remove 99.97% of particles that are 0.3 microns or larger in size; This includes particles such as smoke, bacteria, and viruses. Since HEPA filters are so efficient, they cause a higher pressure drop than filters with MERV ratings. Given their high efficiency, HEPA filters are best suited for rooms where air quality is a concern, such as in hospitals, laboratories, and cleanrooms.

Many HVAC systems are not designed for HEPA filters, but these filters are available as portable air cleaners or vacuum cleaners. They can be used in homes to improve indoor air quality, particularly for people with allergies or respiratory issues.

Pros of HEPA HVAC Filters:

They’re highly effective at capturing airborne particles, including viruses and bacteria.
They’re ideal for people with allergies or respiratory issues.

Cons of HEPA HVAC Filters:

Not as cost-effective.
Decreased HVAC airflow.

Electrostatic Air Filter vs. HEPA: Which is Better?

Both the electrostatic air filter and HEPA filter have their strengths and weaknesses. The choice between the two will depend on your specific needs. However, the Blade Air Pro Filter Series is the best option for businesses looking for energy savings and easier maintenance while maintaining better filtration than traditional filters. You can improve indoor air quality while lowering energy consumption by up to 75% and reducing maintenance costs by up to 35%.

Utilizing active polarization fields to bind the micro-particulates together that standard filters let pass, capture and kill viruses, bacteria, mould, and removes VOCs and other harmful particulates. This field binds the micro-particulates together, deactivates the viruses/bacteria and traps them in the filter.

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