The effects of poor indoor air quality in classrooms has been known for years. Chronic illnesses, reduced cognitive abilities, sleepiness and increased absenteeism have all been attributed to poor IAQ.
With students and teachers spending about half of their waking hours at school or work, it's important to view indoor air quality as a top priority. Below, we have collected some of the most recent case studies, so you too can understand the direct effects of high CO2 levels and its influence on indoor air.
Why Classroom Ventilation is Essential for Student Learning
Proper classroom ventilation does far more than improve comfort - it directly supports student learning, teacher performance and overall health. Every student and teacher continuously exhales carbon dioxide (CO2) and without adequate outdoor air ventilation, CO2 concentrations naturally increase throughout the school day.
As ventilation decreases, classrooms may begin to feel warm, stuffy and uncomfortable. Elevated CO2 levels are often associated with reduced attention, slower decision-making, fatigue and decreased cognitive performance, making it more difficult for students to stay engaged and absorb new information.
Maintaining effective ventilation helps dilute indoor contaminants, remove excess carbon dioxide and create healthier learning environments where students and educators can perform at their best.
Schools that routinely evaluate ventilation performance and monitor indoor air quality are better equipped to provide safe, comfortable classrooms while supporting improved attendance, academic success and occupant well-being.
What is the standard CO2 indoor air quality?
To minimize the risk of airborne transmission of viruses, CO2 levels should be measured at a specific threshold indoors. It is recommended to stay most close to 400ppm (outdoor CO2 concentration) and below 800ppm. If the threshold is exceeded, it is recommended to ventilate the space, leave the room, and renew the air.
Current ventilation guidelines however, such as those from the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) recommend that indoor CO2 levels not exceed the local outdoor air concentration by more than about 650ppm.
Carbon Dioxide Levels in the Classroom
This table further shows the different CO2 levels and their impact on human health.
Note that while levels above 5,000ppm almost never occur in an environmental setting, CO2 levels above 2,000ppm in closed classrooms are not uncommon.
| 400ppm | Normal outdoor air |
| 400-1,000ppm | Typical CO2 levels found indoors |
| 1,000-2,000ppm | Common complaints of drowsiness or poor air quality |
| 2,000-5,000ppm | Associated with headaches, fatigue, stagnant, stuffiness, poor concentration, loss of focus, increased heart rate, nausea |
| > 5,000ppm | Toxicity or oxygen deprivation may occur. This is the permissible exposure limit of the daily workplace exposure |
| > 40,000ppm | Immediately harmful due to oxygen deprivation |
Building codes in most states reference Standard 62, either in part or in its entirety, as part of their definition for minimum ventilation requirements.
According to ASHRAE, the recommended CO2 level in buildings should be no more than 700 parts per million (ppm) above outdoor air. Since outdoor air is approximately 400ppm, indoor CO2 levels should be no more than 1,100 ppm.
Note that this guideline is not designed to limit the amount of CO2, but rather to indicate that a proper level of clean air (15-20 CFM/person) is being distributed in indoor spaces like classrooms. And OSHA and the US Green Building Council have even tighter indoor CO2 recommendations.
Following on our research on IAQ in schools additional studies are now being focused on how to control the transmission of airborne infectious diseases indoors, specifically in the classroom or university setting.
Similar to to the CO2 research, the results demonstrate that once viruses are present in the classroom you have two choices:
- Ventilate the building (bring fresh air in from outside) or
- Remove the virus from the air inside the building (filtration/HVAC systems)
Currently, additional inspection criteria and standards are being developed, like that of the New York City Department of Health and Mental Hygiene. These standards are based on guidance by the CDC and WHO to ensure proper monitoring systems are in place in classrooms and group spaces to achieve sufficient ventilation.
The New York City standard states, "Proper air ventilation is key to stop the spread of airborne viruses."
Per CDC guidance, it is highly recommended that schools:
- Increase the amount of fresh air in classrooms
- Inspect, repair, and increase air filtration
- Inspect and repair supply and exhaust fans
- Deploy portable High-Efficiency Particulate Air (HEPA) filters
- Install Indoor air quality monitoring devices
- Ensure ventilation systems operate properly and provide acceptable indoor air quality for the current occupancy level for each space
Health Effects of Poor Air in Schools
Both short and long term exposure to poor air quality can lead to a wide range of negative health effects. As seen in many research studies, poor air quality can also cause student irritation in the nose, throat, eyes, aggravate asthma, affect heart rate, and cause ongoing airborne illness.
The 5 main health effects of poor air quality include:
- Headaches
- Fatigue
- Dizziness
- Asthma
- Sick Building Syndrome
How common is poor IAQ and high CO2 levels?
While exact figures are not known, according to the National Center for Education Statistics there are almost 99,000 public K-12 schools in America, and the average school building is at least 42 years old.
Of these 30% reported heating systems, air conditioning systems, and ventilation/filtration systems to be in fair to poor condition.
One of the reasons, is that many school buildings were built in the 1960s and 1970s to solve two problems: the increasing number of "baby boomer" children coming into the public school system, and the increasing cost of energy needed to heat or cool older school buildings.
To solve these problems new schools built during those years used "modern" energy-saving features like windows that could not be opened. While "closing the envelope" reduced the cost to heat and cool the buildings, ironically, it resulted in sealed classrooms that trapped poor air quality, contaminants, and drove up CO2 levels past acceptable limits.
ASHRAE School Indoor Air Quality Requirements
The American Society of Heating, Refrigeration, and Air Conditioning Engineers, is a global professional society that sets standards for building performance. Of its standards it places high emphasis on educational buildings and ventilation requirements to improve indoor air quality for students, faculty, and staff.
In its requirements ASHRAE states, "Classrooms should have a minimum ventilation rate of 15 cubic feet per minute per person". The Building Energy Efficiency Standard, also known as Title 24, has the same requirement for universities as well.
In addition to minimum ventilation rates, ASHRAE also recommends that school staff take the following actions to improve indoor air quality and ventilation:
- Periodically test and adjust school HVAC equipment.
- Ensure that building control systems and thermostats are programmed to operate ventilation fans one hour before school starts and continuously during the school day.
- When possible, use filters with a minimum efficiency rating value, or MERV, of 13 or greater to remove small particles from the air. (Change filters every 3-4 months).
- Install CO2 monitors in classrooms to continuously monitor CO2 levels and detect potential ventilation problems.
- If needed, supplement filtration with portable air cleaners.
Why Schools Should Continuously Monitor Indoor Air Quality
Pictured above: Wireless Indoor Air Quality Monitor for Schools
Indoor air quality changes throughout the day as classroom occupancy, weather conditions, HVAC operation and ventilation rates fluctuate.
A single CO2 reading provides only a snapshot of conditions, while continuous air quality monitoring allows school administrators and facility managers to identify recurring ventilation issues before they affect students or staff.
Continuous indoor air quality monitoring helps schools:
- Verify classroom ventilation performance
- Detect HVAC system issues early
- Improve student concentration and classroom comfort
- Support healthier indoor learning environments
- Reduce complaints related to headaches, fatigue and poor air quality
- Document indoor environmental conditions for facility management and maintenance planning.
Many modern indoor air quality monitors measure carbon dioxide (CO2), temperature and relative humidity in real time, allowing educators and maintenance personnel to make informed decisions about ventilation throughout the school day.
As more and more studies continue to show the negative effects of poor indoor air quality, not only does poor air circulation result in high levels of CO2 but also high levels of airborne illness.
Unfortunately, studies have also shown that many universities, classrooms, and indoor learning centers do not have the proper ventilation rates to begin with.
This has resulted in increases in child illness, lack of productivity, and uninterest in learning. Additionally, a review of referred archival journals commissioned by Berkeley Lab for their Scientific Findings Resource Bank concluded that:
The available research provided “compelling evidence of an association of improved student performance with increased classroom ventilation rates.” Overall, eight out of 11 studies reported statistically significant improvements in at least some measures of student performance with increased ventilation rates or lower carbon dioxide concentrations, and a ninth study reported a statistically significant improvement in performance when applying a less stringent than typical criterion for statistical significance. Five of the studies were intervention studies that increased ventilation rates and measured changes in performance within students.
State School Indoor Air Quality Standards
While there are many individual programs, requirements, and tools surrounding improved indoor air in schools particular standards have been set in place by specific state and local jurisdictions as well. Whether or not your state or locality have begun to put specific standards in place, we recognize that it will not be long before the majority of the states are following other set standards, and below, are specific examples of states where programs have started for indoor air quality (IAQ) guidelines.
- California: California Submittal Requirements for Schools
- New Jersey: Indoor Air Quality Guidelines for schools, engineers, and architects
- Massachusetts: Indoor Air Quality (IAQ) Response Protocol
- Pennsylvania: Penn State Indoor Air Quality Requirements
- South Carolina: Indoor Air Quality University Requirements
- Washington: School Indoor Air Quality Best Practice Manual
How to Improve Indoor Air Quality in Classrooms
The simplest solution is to talk to the building supervisor in your child’s school. Indoor air quality is normally monitored in all school buildings, and the results are available to the public. Additionally, you can research online "indoor air quality in schools (your state)" or visit healthyschools.org.
For educators and administrators looking for an indication of proper indoor air quality, indoor air quality monitors can be used to properly monitor and measure carbon dioxide, temperature, and relative humidity.
By utilizing an indoor air quality monitor, you can rest assure that should classroom levels exceed the normal threshold, the device will provide a prompt indication.
Additional advantages of a CO2 Monitor include:
- Advanced sensor technology (using NDIR sensing capabilities)
- Large LCD display for teachers, students, faculty for real-time levels
- Easy to use, "plug-and-play" capabilities, monitors in minutes
- ECO saving power function darkens the LCD during periods of non-use
Benefits of Air Quality Monitors in Classrooms
When reflecting on what is happening across the world as we still continue to battle the pandemic, it is important to improve the quality and health of indoor air for our teachers, students, faculty, and staff members.
When you implement air quality monitoring you can ensure safe operation in schools and maintain healthy facilities that include adequate ventilation, mitigate risk of virus exposure, and create healthier learning environments.
Currently, CO2Meter indoor air quality monitors continue to be used across universities, research facilities, and classrooms to provide monitoring and benefits such as:
- Determining the risk of airborne viruses within individual classrooms
- Monitoring classrooms simultaneously for ventilation indication
- Creating a more productive and focused environment for students
- Making parents feel confident in the air quality their children are breathing
- Enabling a safer and healthier "back-to-school" program
For further information on monitoring indoor air quality, and ventilation best practices in your home, school, or office space, contact Sales@CO2Meter.com
Frequently Asked Questions about Indoor Air Quality in Schools
Why is indoor air quality important in schools?
Students and teachers spend six to eight hours each day inside classrooms, making indoor air quality a critical factor in health, comfort, and academic performance. Poor indoor air quality can contribute to headaches, fatigue, respiratory irritation, increased absenteeism, and reduced concentration. Maintaining healthy indoor air supports better learning environments and overall student well-being.
What is a good CO2 level in a classroom?
Outdoor carbon dioxide concentrations are typically around 400 - 450ppm. Many indoor air quality professionals recommend maintaining classroom CO2 levels below 800 - 1,000ppm, depending on occupancy and ventilation conditions.
Rising CO2 levels often indicate that additional fresh outdoor air may be needed.
Does high CO2 affect student learning?
Research has shown that elevated indoor CO2 concentrations and inadequate ventilation are associated with reduced cognitive performance, decreased attention, slower decision making and lower academic performance. Maintaining good ventilation helps students remain focused and engaged throughout the school day.
How often should classroom air quality be monitored?
Indoor air quality should ideally be monitored continuously during occupied hours. Continuous monitoring provides real-time information about ventilation performance and changing classroom conditions, allowing schools to respond quickly if CO2 concentrations begin to increase.
What causes poor indoor air quality in schools?
Common causes include inadequate ventilation, aging HVAC systems, overcrowded classrooms, elevated carbon dioxide levels, excess humidity, mold, dust, volatile organic compounds (VOCs) and outdoor pollutants entering the building. Older school buildings may be particularly susceptible if ventilation systems have not been modernized.
What should a classroom air quality monitor measure?
An effective classroom indoor air quality monitor should measure carbon dioxide (CO2), temperature and relative humidity at a minimum. Some advanced monitors also measure volatile organic compounds (VOCs), particulate matter (PM2.5) and other environmental indicators that contribute to overall indoor environmental quality.
How can schools improve indoor air quality?
Schools can improve indoor air quality by increasing outdoor air ventilation, maintaining HVAC systems, replacing air filters on schedule, monitoring classroom CO2 levels, controlling indoor humidity, using portable HEPA air cleaners where appropriate and reducing indoor pollutant sources such as excessive dust, mold, and high-emission cleaning products.
Why do schools use CO2 monitors?
Carbon dioxide monitors provide a simple way to evaluate whether classrooms are receiving enough fresh outdoor air. Since people naturally exhale CO2, increasing concentrations often indicate insufficient ventilation. Real-time monitoring allows teachers and facility managers to identify ventilation issues early and improve classroom comfort before students begin experiencing symptoms of poor indoor air quality.
Resources:
- https://www.co2meter.com/blogs/news/indoor-air-quality-standards-schools
- https://www.co2meter.com/blogs/news/high-carbon-dioxide-co2-levels-indoors
- https://www.energy.wsu.edu/documents/co2inbuildings.pdf
- https://www.dhs.wisconsin.gov/chemical/carbondioxide.htm#:~:text=The%20levels%20of%20CO2,of%20drowsiness%20and%20poor%20air.
- https://www.epa.gov/iaq-schools/reference-guide-indoor-air-quality-schools
- https://www.ambius.com/blog/why-schools-need-clean-air-indoors/
- https://pubmed.ncbi.nlm.nih.gov/21621987/
- https://www.ashrae.org/file%20library/about/position%20documents/pd_indoorcarbondioxide_2022.pdf
- https://www.ashrae.org/file%20library/about/government%20affairs/public%20policy%20resources/briefs/approved-ppib---indoor-carbon-dioxide.pdf
- https://www.studyfinds.org/classrooms-worse-air-quality/
- https://www.epa.gov/iaq-schools
- https://www.co2meter.com/collections/indoor-air-quality
