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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

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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.

Ventilation and Health: Air Ventilation For Closed Room 

  • Writer: Jennifer Crowley
    Jennifer Crowley
  • Aug 2, 2023
  • 5 min read

Updated: Jul 8, 2024

Middle-aged white female massaging her eyes while holding her glasses in the other hand, clearly in discomfort
Long-term exposure to indoor air pollutants may also contribute to more severe health conditions, such as cardiovascular diseases and even certain cancers.

Take a deep breath. Can you be sure that the air you’re breathing right now is clean and fresh?


For many of us, especially those spending significant time indoors, the quality of the air we breathe can profoundly impact our overall health and well-being.

Indoor air quality is a crucial aspect of maintaining a healthy living environment. It becomes even more critical when dealing with closed rooms, where natural air circulation is limited. Below, we will explore the vital link between ventilation and health, shedding light on how closed-room air quality can significantly affect our well-being.


Throughout this article, we aim to delve into the direct and indirect health effects of poor indoor air quality in closed spaces and discuss the role of proper ventilation in ensuring a healthier and more comfortable living space.


The Link Between Indoor Air Quality and Health

Indoor air quality refers to the condition of the air within buildings and structures indoors, particularly as it relates to the health and comfort of occupants. Poor air quality can arise from various factors, such as inadequate ventilation, the presence of pollutants, and excess moisture. The consequences of breathing in polluted indoor air can be far-reaching.


Common health issues associated with poor ventilation in closed rooms include allergies, asthma exacerbation, respiratory problems, headaches, and fatigue. Long-term exposure to indoor air pollutants may also contribute to more severe health conditions, such as cardiovascular diseases and even certain cancers.

According to the World Health Organization (WHO), household air pollution was responsible for an estimated 3.2 million deaths per year in 2020, including over 237,000 deaths of children under the age of 5.


How Ventilation Impacts Indoor Air Quality

Ventilation is the process of bringing fresh outdoor air into an indoor space and removing stale air, ensuring a continuous exchange of air to maintain optimal air quality.


Adequate ventilation facilitates proper air circulation in closed rooms, preventing the accumulation of stagnant air and the buildup of pollutants. It helps distribute fresh air throughout the space, ensuring all occupants can access clean, oxygen-rich air.


One of the primary roles of ventilation is to remove indoor air pollutants. Effective ventilation systems can filter out dust, pollen, mould spores, pet dander, and other allergens, making the air healthier to breathe.


The Role of Closed Room Ventilation in Enhancing Well-being

Imagine a stuffy and poorly ventilated room where the air feels heavy and stale. Proper ventilation, on the other hand, creates a comfortable and pleasant environment. Adequate airflow can help regulate temperature, reduce humidity levels, and minimize stuffiness, contributing to an overall sense of comfort and relaxation.


The quality of the air we breathe has a direct impact on cognitive function and productivity. In well-ventilated rooms, where fresh air is consistently supplied, occupants experience improved focus, better decision-making abilities, and enhanced creativity. On the contrary, inadequate ventilation can lead to brain fog and reduced productivity.


The relationship between indoor air quality and mental health is increasingly evident. Studies have shown that exposure to clean air and natural ventilation can alleviate stress, anxiety, and depression. Good ventilation promotes a sense of openness and connection to the outdoors, which can positively affect mood and overall mental well-being.


Signs of Poor Ventilation in Closed Rooms

Identifying the signs of poor ventilation in closed rooms is crucial to address potential air quality issues.


If you or your family members experience frequent headaches, dizziness, coughing, or worsening allergies while indoors, it might indicate inadequate ventilation and poor air quality.


Additionally, these signs are usually indicative of a home that has poor ventilation:

  1. Condensation on windows and glass

  2. Discolouration of the floor, wall tiles, and grout

  3. Early signs of rust stains on plumbing

  4. Mould

  5. Strong odours that don’t dissipate

  6. Heat build-up that doesn’t dissipate


Types of Ventilation

Different types of indoor space ventilation methods are available, each offering unique benefits and suited to specific room layouts and requirements. Understanding these ventilation options can help you make an informed decision about the best system for your closed room.


1. Natural Ventilation

Natural ventilation relies on passive methods to facilitate the exchange of indoor and outdoor air. It typically involves strategically placed windows, doors, and vents to allow fresh air to enter the room and stale air to exit. The principle behind natural ventilation is based on wind pressure and temperature differences, creating a natural airflow.

Advantages

  1. Energy Efficiency: Natural ventilation doesn’t require electricity or mechanical systems, making it an eco-friendly and cost-effective option.

  2. Connection to the Outdoors: It provides a direct link to the outside environment, allowing occupants to enjoy fresh air and natural sunlight.


2. Mechanical Ventilation

Mechanical ventilation systems involve the use of fans and mechanical components to circulate and exchange air. There are three main types:

  1. Exhaust Fans: These are installed to expel indoor air and pollutants directly outside, often used in kitchens, bathrooms, and utility rooms.

  2. Supply Fans: These fans bring in fresh outdoor air and distribute it throughout the closed room. They work well in spaces with limited access to natural ventilation.

  3. Balanced Systems: Balanced ventilation systems combine both exhaust and supply fans to maintain a balanced airflow. They ensure a constant supply of fresh air while expelling stale air.

Advantages

  1. Control over Airflow: Mechanical ventilation allows precise control of airflow, enabling optimal ventilation rates.

  2. Filtering Capability: Mechanical systems can be equipped with filters to remove allergens, dust, and pollutants, enhancing indoor air quality.


3. Hybrid Ventilation

Hybrid ventilation is a blend of natural and mechanical methods. It seeks to optimize airflow and energy efficiency by adapting to varying external and internal conditions. For example, a hybrid system might use natural ventilation during mild weather and switch to mechanical ventilation during extreme weather conditions.

Advantages

  1. Energy Efficiency: Hybrid systems can reduce energy consumption by intelligently utilizing natural ventilation when conditions permit.

  2. Consistent Airflow: The combination of natural and mechanical methods ensures a steady and controlled airflow.


Tips for Improving Closed Room Air Ventilation

  1. Ensure proper airflow by keeping doors and windows open when possible to allow fresh air to circulate.

  2. Use exhaust fans in kitchens and bathrooms to remove excess moisture and odours.

  3. Consider installing a mechanical ventilation system, such as a balanced ventilation system with heat recovery, to maintain fresh air circulation in closed rooms without compromising energy efficiency.


Best Practices for Maintaining Good Air Quality in Closed Rooms

Regular Cleaning – Regularly clean and dust your living space to reduce the buildup of allergens and pollutants.

Plants and Natural Solutions – Introduce indoor plants known for their air-purifying properties, such as spider plants, peace lilies, or snake plants. Natural solutions like opening windows for cross-ventilation on breezy days can also help improve air quality.

Air Purifiers and Ventilation Systems – Consider investing in high-quality air purifiers and ventilation systems tailored to your room’s size and specific needs.

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.

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