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.

Indoor Air Quality (IAQ) in Schools: Student Health and Performance

Jennifer Crowley
Jul 28, 2023
4 min read

Updated: Jul 9, 2024

rear room view of an elementary classroom with various student's hands raised and the female teacher blurred at the front of the classroom — Students exposed to poor Indoor Air Quality may experience difficulty concentrating, fatigue, and a decline in productivity and overall well-being.

Indoor air quality (IAQ) is a critical yet often overlooked aspect of educational environments. The quality of air inside schools has a direct impact on student health and academic performance. In this blog, we will explore the significance of IAQ in schools and how it influences students’ well-being and learning outcomes.

To comprehend the importance of IAQ, it’s crucial to understand its components. IAQ refers to the condition of the air within buildings, including its purity, temperature, humidity, and ventilation.

Sources of Indoor Air Pollution in Schools

Sources of indoor air pollution in schools can vary, but here are some common ones:

Building Materials: Some building materials used in schools, such as certain types of paint, adhesives, and flooring materials, can emit volatile organic compounds (VOCs) that contribute to indoor air pollution
Cleaning Products: Cleaning chemicals, including disinfectants, floor cleaners, and aerosol sprays, often contain harmful chemicals that can release fumes and particles into the air, affecting indoor air quality.
HVAC Systems: Poorly maintained heating, ventilation, and air conditioning (HVAC) systems can accumulate dust, mould, and other contaminants, which are then circulated throughout the building, compromising air quality.
Mould and Moisture: Moisture problems, such as leaks or high humidity levels, can lead to the growth of mould and mildew. These can release spores and mycotoxins into the air, posing health risks.
Pests and Pest Control: The presence of pests like rodents and insects in schools can introduce allergens and contaminants. The use of pesticides and insecticides for pest control can also contribute to indoor air pollution.
Outdoor Air Pollution: Pollutants from outdoor sources, such as vehicle emissions and industrial activities, can infiltrate schools through poorly sealed windows, doors, or ventilation systems, compromising indoor air quality.
Combustion Sources: Schools with combustion appliances, such as furnaces, boilers, or stoves, can emit pollutants such as carbon monoxide (CO), nitrogen dioxide (NO2), and particulate matter, which can be harmful when not adequately vented.
Personal Care Products: Students and staff using personal care products, such as perfumes, colognes, and hair sprays, can contribute to indoor air pollution by releasing VOCs.
Classroom Supplies: Various classroom supplies, including art materials, science lab chemicals, and glues, may contain hazardous substances that can release fumes or particles when used.
Outdoor Contaminants: Pollen, allergens, and pollutants brought in from outdoors on clothing, shoes, or through open doors and windows can contribute to indoor air pollution.

It’s essential for schools to identify and mitigate these sources of indoor air pollution through adequate ventilation, regular maintenance, proper cleaning protocols, and the use of low-emission materials and products.

Impact of Poor IAQ on Students

Graphic illustration showcasing the various IAQ elements that affect Children vs Adults — Illnesses caused by poor IAQ have resulted in more sick days, from school, due to respiratory-related health problems.

Poor IAQ can have severe consequences for student health. It contributes to respiratory issues like asthma and allergies, increases the risk of infections and illnesses, and hampers cognitive function. Students exposed to poor IAQ may experience difficulty concentrating, fatigue, and a decline in overall well-being.

Student Health

According to the EPA, the term “sick building syndrome” (SBS) describes situations in which building occupants experience acute health and comfort effects that appear to be linked to time spent in a building, but no specific illness or cause can be identified.

Sick building syndrome has been reported by students in schools with poor IAQ. It is a condition that impacts employees or students that spend a lot of time indoors and is caused by unhealthy or stressful factors, i.e. poor ventilation. Illnesses caused by poor IAQ have resulted in more sick days, from school, due to respiratory-related health problems.

Cognitive Development and Academic Performance

Lack of adequate ventilation has been associated with poor cognitive development, especially in primary school age groups. An experiment was conducted through a Texas school district to improve the air quality condition in schools, which determined that IAQ improvements resulted in improved standardized test performance.

In another experiment, the average ventilation improvement project improved math and reading scores by 0.07 standard deviations (SDS) and 0.11 SDS, increasing the probability of passing these tests by 2–3%.

Increased Risks of Asthma and Respiratory Issues

Respiratory problems such as asthma are also aggravated due to air pollution in schools. A study has shown the possibility of reducing asthma incidents from 16% to 13% among children by simply applying filters for PM 2.5 in the classrooms.

Other respiratory health effects include:

Coughing
Difficulty breathing
Airway inflammation & irritation
Irregular heartbeat
Lung damage

Simple Solutions to Help Manage Indoor Air Quality in School Classrooms

Mechanical Ventilation

Mechanical ventilation uses ducts and fans to draw in and distribute fresh air, and can even exhaust air from specific areas. In schools, mechanical ventilation uses HVAC systems or unit ventilators. To further enhance ventilation levels, air purification systems can be installed within existing ventilation systems or unit ventilators to achieve better air quality and reduce indoor air pollution levels.

Natural Ventilation

Simply opening a window or door encourages better airflow within an enclosed room. A study completed in 2017 proves a significant improvement in IAQ, specifically CO2 levels in a room with a group of 4-6 persons, by simply opening a window.

Illustration of how cross ventilation works, pulling air in from an open window and ventilating the rooms air through another open window — Cross ventilation allows a breeze to enter, flow through and exit within an enclosed area.

Additionally, cross ventilation is a highly effective method of promoting good airflow; Allowing a breeze to enter, flow through and exit within an enclosed area. This ventilation method encourages continuous airflow by pulling air from openings on one side of a building and through to the other.

Regular Cleaning & Dusting

Preventing any buildup of animal dander, dust mite matter, and pollen can improve indoor air quality. The American Lung Association recommends incorporating dusting into your regular cleaning routine, which can reduce the amount of dust and improve overall indoor air quality in your home.

Natural Cleaning Products

Substitute bi-products with natural-based products for cleaning agents to reduce indoor VOCs. A study conducted in Brisbane, Australia, in over 25 primary schools – to identify the VOCs’ sources – deduced that chemical-based cleaning products alone caused 41% of indoor VOCs. The synthetic fragrances found in cleaning and maintenance products contribute to air contamination.

Building Design

The design of school and childcare facilities can contribute to minimizing children’s exposure to air pollution while onsite. This may entail locating the most frequented rooms or areas as far away from road traffic as possible, shielding the playground behind buildings, walls or green infrastructure (i.e. using plants), and allowing natural ventilation patterns that promote pollutant dispersion. Green infrastructure can filter some air pollutants and alter the airflow — thus changing pollution concentrations in local microenvironments.

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