top of page

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

Tags

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. PNASNature


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:

  1. Dilute what’s in the room (ventilation/outdoor air)

  2. Remove what’s in the room (filtration/air cleaning)

  3. 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+1Environmental 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.

The Impact of Wildfires on Indoor Air Quality (IAQ): What You Need to Know

  • Writer: Jennifer Crowley
    Jennifer Crowley
  • Jul 28, 2023
  • 3 min read

Updated: Jul 9, 2024

Aerial view of an uncontrolled wildfire with massive clouds of toxic smoke
For people in close proximity to a wildfire, there’s a danger from breathing gaseous chemicals the fire emits. These include carbon monoxide, methane, acetic acid and formaldehyde.

For the most up-to-date information, including which fires are out of control, visit Alberta’s Wildfire Status Dashboard.


Wildfires are an ever-present threat in many parts of the world, and they have become increasingly frequent and severe in recent years. While the immediate impact of wildfires is often devastating, with homes and communities destroyed and lives lost, the longer-term effects on the environment and public health can also be significant.


One such impact is the effect on indoor air quality, which can have severe consequences for the health of individuals and families. In this blog, we will explore the impact of wildfires on indoor air quality and discuss what you need to know to protect yourself from the harmful effects of wildfire smoke.


What is Wildfire Smoke and What is the Impact of Wildfires on Your Indoor Air Quality?

Wildfire smoke is a complex mixture of gases, particles, and water vapour that contains:

  1. Ozone

  2. Sulphur Dioxide

  3. Nitrogen Dioxide

  4. Carbon Monoxide

  5. Volatile Organic Compounds (VOCs)

  6. Fine Particulate Matter (PM2.5)


These pollutants can harm your health, with PM2.5 posing the most significant risk. The larger or “coarse” particles in smoke irritate the eyes, nose and throat but generally don’t reach the lungs. However, the “finer” particles, a fraction of a human hair’s diameter, can wreak havoc. These tiny particles can be inhaled deep into the lungs and eventually make it into the bloodstream, making healthy people sick and sick people sicker.


There is no evidence of a safe level of exposure for most of these pollutants. This means that smoke can impact your health even at very low levels. As smoke levels increase, your health risks increase. Air quality may be decreased even if you can’t see or smell smoke.


For people in close proximity to a wildfire, there’s a danger from breathing gaseous chemicals the fire emits. These include carbon monoxide, methane, acetic acid and formaldehyde.


Symptoms of Wildfire Smoke Exposure

The more common symptoms of smoke exposure include:

  1. Headaches

  2. A Mild Cough

  3. A Runny Nose

  4. Production of Phlegm

  5. Eye, Nose and Throat Irritation


The symptoms typically associated with smoke exposure are primarily due to the irritation of the mucous membranes and respiratory tract by the fine particles contained in the smoke. Furthermore, toxic gases found in smoke, such as formaldehyde and acrolein, can exacerbate respiratory distress. It is important to note that even low levels of exposure to carbon monoxide can lead to chest pain and irregular heartbeat, especially for those with pre-existing heart conditions.


More serious health concerns can include:

  1. Dizziness

  2. Chest Pains

  3. Severe Cough

  4. Shortness of Breath

  5. Wheezing (including asthma attacks)

  6. Heart Palpitations (irregular heartbeat)


Who is most at risk?

Some people are at a higher risk of health problems when exposed to wildfire smoke, including:

  1. Seniors: the elderly are more likely to have pre-existing heart or lung conditions; they are more susceptible to the harmful effects of wildfire smoke.

  2. Pregnant women

  3. Infants and young children: exposure to smoke is especially hazardous for children with asthma and may cause more frequent or severe asthma attacks. Children, in general, may experience shortness of breath, coughing and wheezing when exposed to smoky air.

  4. People who work outdoors

  5. People involved in strenuous outdoor exercise

  6. People with existing chronic health conditions: individuals with heart disease and chronic lung diseases like asthma and emphysema; studies have linked high levels of particulate matter with decreased lung function, worsening asthma symptoms, irregular heartbeat, heart attacks and even premature death.


How to reduce your exposure to wildfire smoke?

The best way to protect your health is to reduce your exposure to wildfire smoke indoors. This can include doing the following:

  1. Keep windows and doors closed as long as the temperature is comfortable.

  2. Use recirculation settings on your HVAC system to prevent smoke from entering your home.

  3. Use a clean, good-quality air filter in your HVAC system.

  4. Use an air purifier with HEPA filtration to remove smoke from your home.

Explore expert insights, stay up to date with industry events, and gain a deeper understanding of the cutting-edge developments that are revolutionizing the indoor air quality landscape within Blade Air's comprehensive Insights Hub.

You can also subscribe to our monthly newsletter below for exclusive early access to Blade's Insights content, uncovering tomorrow's air quality advancements before they hit our Hub.

Insights Hub

Lorem ipsum dolor sit amet, consec tetur adipiscing elit. Sit quis auctor 

Lorem ipsum dolor sit amet cotetur 

Lorem ipsum dolor sit amet, consec tetur adipiscing elit. Sit quis auctor 

Lorem ipsum dolor sit amet cotetur 

Lorem ipsum dolor sit amet, consec tetur adipiscing elit. Sit quis auctor 

Lorem ipsum dolor sit amet cotetur 

bottom of page