How Crowded Classrooms Affect Indoor Air Quality

How Crowded Classrooms Affect Indoor Air Quality

In the winter, windows are shut and heating systems run all day and night. The germs students and staff bring to school circulate repeatedly. Viruses thrive in both low and high relative humidity. Air filters do what they can, but the best HEPA filters aren’t always suitable for older heating systems.

Viruses are only a small part of the problems students and teachers face with indoor air quality. Many diseases spike in winter for a reason, and the school’s HVAC system plays a role. Many schools don’t have HVAC systems. They rely on older, antiquated heating systems. Air Blue is equipped to help any school in the Chicago area with their air quality issues. 

The Unseen Problem in Chicagoland Schools

It’s another dreary, rainy Chicago fall or winter day. Windows are tightly closed to keep out cold, drafty air while the heating system works hard to warm each room. Students are packed into the classroom. It’s warm inside, and students and teachers exhale warm, humid air all day, adding germs and extra humidity.

Those closed windows help keep the heat in, but they also keep germs, odors, humidity, and other airborne contaminants like dust, mold spores, and pet dander inside. Every student carries particles from home. It might be pet dander, stale tobacco smoke from family members who smoke indoors, or heavily-scented body sprays or hair products. 

Without an HVAC system to filter out germs, allergens, and irritants, the air can irritate the respiratory system. Students with allergies, asthma, or weakened immune systems are all at risk.

As student illnesses increase, teachers have to make sure students who stay home don’t fall far behind those who come to class. Students in class need to remain engaged and not feel that a sick student is holding them back. School districts face this problem each year.

What Happens to Air Quality in a Crowded Classroom?

Allergens and germs are only part of the air-quality problem. Air quality itself also matters. People in a crowded classroom breathe in oxygen and expel carbon dioxide, which raises CO2 levels. 

Classrooms often have CO2 monitors, and when the levels exceed 1,000 ppm, drowsiness and headaches occur. It can impact a student’s concentration and lead to lower test scores, which isn’t ideal when the environment is supposed to encourage learning.

Damp coats and boots, high humidity levels, and warm room temperatures also encourage mold and mildew growth. If mold starts growing in the duct system or in ceiling tiles, it can impact any child or adult with a mold allergy.

If the heating system uses natural gas or propane, it can produce high carbon monoxide levels. In 2025, carbon monoxide detectors went off at an elementary school in Texas. The students were evacuated with no serious illnesses. Working carbon monoxide detectors save lives. 

Every school needs them and should test them regularly. State law requires hardwired carbon monoxide alarms for buildings constructed after January 1, 2016. Older buildings can use battery-powered alarms. Regular inspections and maintenance of gas-fired heating systems are essential.

Chicagoland Schools and the Most Common HVAC Challenges

Many Cook and DuPage County school buildings are older and don’t have modern HVAC systems. The average age of a Chicago Public Schools building is 84 years, adding to the HVAC challenges school administrators face.

Outdated Heating Systems

Many Chicagoland schools have boilers over 30 years old. When a school relies on boilers, it often lacks AC or filtered ducts to help remove contaminants. These older systems are not designed for today’s classroom density.

Sudden Shifts in Temperature

Chicago experiences wide temperature swings. You can go from heat and humidity one month and have freezing temperatures and even snow a month or two later. A stretch of rainy, cool days has the maintenance team cranking up the heat. 

If there’s another sudden late-autumn warm-up, the heat goes off, windows open, and the cycle continues. Each time the heat turns back on, it runs hard. These sudden startups put extra strain on motors, fans, belts, and pumps.

Tightly Sealed Buildings

Keeping cold air out and warm air in often starts with insulation and sealing drafts around windows and doors. It keeps heat in, but it also keeps stale air inside. The lack of ventilation can trap indoor pollutants.

HVAC Upgrades for Healthier Air in the Classroom

Upgrading to an energy-efficient HVAC system is ideal, but few school districts have the funds available for a complete switch. You can improve air quality without a full HVAC replacement.

• Advanced Filtration: Upgrading HVAC filters to MERV 13+ helps capture more fine particulates and pathogens without impacting the HVAC system’s air pressure. Double-check the highest MERV rating your system allows.
• Air Purifiers: Integrating commercial-grade air purifiers to clean the air in classrooms and neutralize viruses.
• Dehumidifiers: Removing excess humidity from classrooms where humidity levels are extremely high or mold and mildew are issues also helps. Consider collecting the dehumidifier’s water to water office plants.
• Demand-Controlled Ventilation (DCV): CO2 sensors monitor the air quality and pull in fresh air from outside when levels begin to rise. 
• Energy Recovery Ventilators (ERVs): ERVs pre-condition cold winter air using building exhaust to warm the outside air. This removes stale air and humidity while providing fresh, clean air without causing heating bills to soar. 

Students, Teachers, and Administrators All Benefit From Better Air

Chicago has hundreds of elementary, middle, and high schools scattered across the region. Chicago Public Schools District 299 is the largest and averages 24 students per classroom. If you think of the required square footage of a classroom (600 square feet, it makes social distancing challenging. 

Each child and teacher has only about a 23-square-foot space, and droplets from a sneeze travel at up to 50 meters per second and as far as 27 feet. Coughs don’t travel quite as fast or far. They average up to 30 meters per second and go as far as 20 feet. Droplets from a cough can stay airborne for hours if they’re small enough. It makes it easy to spread germs to others in the class.

When teachers get sick, they miss valuable time with their students. Substitute teachers can only do so much. Students who miss school have to catch up on missed lessons, assignments, and homework. Poor air quality puts everyone who misses school at a disadvantage.

Is your school district ready for winter’s surge in stale, germ-ridden air? Contact Air Blue Heating and Cooling for a comprehensive commercial HVAC and indoor air quality assessment. We work around your schedule and price by the job, not the hour, making it easier to handle HVAC repairs and maintenance on a tight budget.