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Ventilation in Schools

Ventilation is one strategy to help prevent and slow the spread of COVID-19 in schools by helping to reduce the number of virus particles in the air. 

Read the TDSB's ventilation report to learn more about the Board's ventilation strategies and investments, as well as details on the ventilation systems and strategies for each school.


The TDSB has focused on several areas to improve ventilation in schools and keep students and staff healthy.

Filtering the Air

  • Installing more than 16,000 HEPA units in TDSB schools to enhance air cleaning and meet the TDSB’s commitment of placing an institutional-grade HEPA filter in every occupied classroom.
  • Ensuring the filters in existing mechanical systems are replaced prior to school starting and increasing the frequency of changing them throughout the year.

Ensuring Heating, Ventilation and Air Conditioning Settings are Maximizing Ventilation

  • Conducting assessments on all mechanical ventilation to ensure they are fully operational and servicing where necessary.
  • Prioritizing repairs for mechanical systems to ensure they are operating efficiently. 
  • Adjusting the operating schedules for all mechanical systems to maximize air flow, increase fresh air intake and increase the amount of air exchanges per day in the building. 
  • Setting the systems to run at maximum outside airflow before school starts and after it ends to refresh the air before arrival and remove remaining particles at the end of the day. 

Maximizing Outdoor Air

  • Encouraging schools to open windows for short periods of time throughout the day to increase ventilation and bring in natural fresh air.
  • Promoting and supporting classes, activities and lunches to be held outside where possible. 

Addressing Local Projects to Improve Ventilation

  • Investing more than $165 million (funded through School Condition Improvement grant and the Covid-19 Resilience Infrastructure funding, received at the end of February 2020).

Of note, CO2 sensors are not installed in TDSB classrooms as this type of monitoring is neither a building code nor a legislative requirement. The widespread use of HEPA filter units in all TDSB classrooms also means that CO2 measurement is even less relevant with respect to assessing infection risk.

Understanding Ventilation Systems

Ventilation is the process of supplying or removing air from a space for the purpose of controlling the indoor air quality within the space. The TDSB has nearly 600 schools that use a variety of ventilation systems based primarily on when the school and any subsequent building additions were built.  The types of ventilation systems commonly in use are:

  • Mechanical Ventilation -- This is ventilation provided by motor-driven fans.  These systems may include supply fans which push outdoor air into a building and exhaust fans which expel air out of a building.  These systems also condition the air through the use of heating and/or cooling equipment so that air is delivered to the space at comfortable temperatures. 
  • Passive Ventilation – This is ventilation, also called non-mechanical or natural ventilation, delivered to the space primarily by air diffusion effects through doors, windows or other intentional openings in buildings.  In TDSB schools, air diffusion effects are often augmented through the use of exhaust fans that assist in drawing fresh air into a building. 
  • Combined Ventilation – Also called partial mechanical ventilation, schools that have had one or more additions built over time may have a combination of mechanical and passive ventilation systems.  Passive ventilation would typically be found in older sections of a school while newer sections would most likely be served by mechanical ventilation systems.

HEPA (High Efficiency Particulate Air) Filters
Regardless of the ventilation system(s) in use at a school, all TDSB classrooms have been equipped with medical-grade, fan-powered HEPA filtration units. HEPA filters are clinically proven to reduce the spread of airborne infections in health care facilities by removing viruses, bacteria and allergens as small as 0.3 microns from the air.  The use of HEPA filtration units, in combination with improved ventilation strategies and existing health and safety protocols, work together to reduce the risk of COVID-19 transmission and support a safer environment for staff and students.