Improving Indoor Air Quality in California Schools4

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HVAC systems provide necessary mechanical ventilation to classrooms. Ventilation helps remove indoor air pollutants such as volatile organic compounds, including formaldehyde, which can off-gas from building materials, finishes, and furniture. There is also increasing evidence that CO2 exhaled by building occupants is an indoor pollutant that can affect cognitive performance. This is particularly important in classrooms, where lots of people gather in a small space.


Millions of California children spend a large portion of their day indoors at school. Ensuring adequate classroom ventilation will help protect and support the health and well-being of students and teachers. Researchers recommend the following actions to improve ventilation rates in classrooms:

  • Complete commissioning and acceptance testing of new HVAC systems as required by Title 24.
  • Run HVAC fans when classrooms are occupied to bring in fresh air.
  • Replace filters 2-3 times per school year.
  • Monitor classroom CO2 concentrations. Thermostats with CO2 sensors and stand-alone sensors are widely available.
  • Test ventilation rates in existing HVAC systems and make corrections when needed.

Goals and Results


With funding from the California Energy Commission, UC Davis and Berkeley Lab researchers visited 104 classrooms in 11 schools throughout California that had been retrofitted with new heating, ventilation and air conditioning (HVAC) units in the past three years. They evaluated the HVAC systems, carbon dioxide (CO2) concentrations, and indoor temperature and humidity through field inspections, monitoring, and a teacher survey.

  • Standards for ventilation rates balance indoor air quality and energy efficiency­­. ASHRAE, a global professional society that sets standards for building performance, specifies a minimum ventilation rate for classrooms of 15 cubic feet per minute per person. In California, the 2016 Building Energy Efficiency Standards, also known as Title 24, have the same ventilation requirement for classrooms. Using measured CO2 concentrations and the number of people in the classroom, researchers found only about 15% of classrooms met the ventilation standard.
  • Researchers characterized each HVAC system by documenting the number of problems due to its hardware, controls and filter maintenance. Classrooms with one or more HVAC problems tended to have lower ventilation rates and higher CO2 levels.
  • In addition to ventilation, thermal comfort impacts student performance. In this study, about 60% of the classrooms were warmer than the recommended average maximum temperature of 73°F. Also, 30% of the teachers surveyed were dissatisfied or very dissatisfied with the temperature in their classroom, and about 10% said the temperature interfered “a lot with the learning environment.”

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