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ASHRAE CO2 Standards for Classrooms

ASHRAE CO2 Standards for Classrooms

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 are CO2 Standards Important in Schools?

Many are aware that their health can be impacted through outdoor air pollution. But what about indoor air pollution? Studies by the U.S. Environmental Protection Agency (EPA) indicate that indoor level pollutants are actually 5x times higher than outdoor air levels. This is a problem since most of us spend a good deal of our day indoors - at home, in an office, or in a classroom.

Research also shows that indoor air pollution is one of the five major environmental risks to the the public health.

This is especially an issue for children in the classroom. Young lungs are particularly vulnerable to air pollution. When exposed, many children start to experience chronic respiratory problems, asthma, fatigue, lack of focus, and become more susceptible to airborne viruses. 

Primary, secondary, and university level classrooms and buildings are all impacted because poor indoor air can directly affect health, performance, and even absenteeism in students, faculty, and staff.

Common sense would tell us that dust, mold, mildew, and airborne viruses like COVID-19 are not good for one's health. But many do not realize the importance of monitoring indoor CO2 levels.

  • High carbon dioxide levels are an easy-to-measure indicator of overall indoor air quality since high CO2 levels correlate with high levels of dust, mold, mildew and airborne viruses.
  • There is a correlation between high carbon dioxide levels and reduced attention and test scores.

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) continues to be an invaluable resource in defining proper CO2 levels for commercial and residential buildings as well as schools, classrooms, and universities.

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 400 ppm (outdoor CO2 concentration) and below 800 ppm. 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



The ASHRAE Standard 62-2001 “provide(s) indoor air quality standards that will be acceptable to human occupants and is intended to minimize the potential for adverse health effects.”

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 formed like that at the University of Colorado focusing 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:

  1. Headaches
  2. Fatigue
  3. Dizziness
  4. Asthma
  5. 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.

Taking Action to Improve Air Quality in Schools

Indoor Air Quality Monitors

Pictured above: IAQMini CO2 Indoor Air Quality Monitor

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.

While studies have shown that high levels of carbon dioxide have reduced the amount of oxygen to the brain, studies have also shown that high levels of airborne illness tend to increase in rooms with poor levels of air circulation. Poor air circulation not only result in high levels of CO2 and viruses, but also high levels of dust, dander, germs, microbes, and other particles.

The ideal indoor environment is one with (you guessed it) lots of outside, fresh air replacing the stale, contaminated air inside. In indoor environments such as classrooms, it is important that quality air quality monitors be placed to indicate should ventilation be required and further, eliminate potential pollutant exposure.

Unfortunately, studies have 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.
Time-average carbon dioxide concentrations in classrooms, Berkeley Lab

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.

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

For educators and administrators looking for an indication of proper indoor air quality, indoor air quality monitors such as the IAQMini CO2 Monitor can be used to properly monitor and measure carbon dioxide, temperature, and relative humidity.

IAQ Mini CO2 Monitor

By utilizing an indoor air quality monitor such as the RAD-0302, you can rest assure that should classroom levels exceed the normal threshold, the device will provide a prompt indication.

Additional advantages of the IAQ Mini CO2 Monitor include:

  1. Advanced sensor technology (using NDIR sensing capabilities)
  2. Large LCD display for teachers, students, faculty for real-time levels
  3. Vibrant 3-color code display (Green/Yellow/Red) to indicate CO2 levels
  4. Easy to use, "plug-and-play" capabilities, monitors in minutes
  5. 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, the RAD-0302 continues 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


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