School HVAC design

Schools are some of the most demanding buildings an HVAC designer works on. Classrooms pack 25 to 30 people into a modest floor area, occupancy swings from full to empty several times a day, and the building sits largely unused for two months each summer. Add tight capital budgets, small maintenance staffs and the fact that the occupants are children who cannot adjust a thermostat or open a window on their own, and the design priorities become clear.

A good school system delivers enough outdoor air to keep students alert, stays quiet enough for teaching, heats reliably through a Prairie or northern Ontario winter, and is simple enough for a district maintenance crew to keep running for 30 years.

Ventilation drives the design

In most Canadian jurisdictions, mechanical ventilation in schools is designed to ASHRAE Standard 62.1 through the reference in Part 6 of the National Building Code (NBC) or the provincial equivalent. The Ventilation Rate Procedure combines a per-person rate with a per-area rate.

Values should always be confirmed against the edition of 62.1 referenced by the governing code. For a typical 75 m2 (800 ft2) classroom with 28 students and a teacher, the breathing-zone outdoor air works out to roughly 190 L/s (400 cfm) before applying zone air distribution effectiveness and system ventilation efficiency. That is a lot of cold air to heat in January, which is why energy recovery matters so much in Canadian schools. See our guide on the ASHRAE 62.1 ventilation rate procedure for the full calculation.

CO2 as a performance indicator

Carbon dioxide concentration is a useful proxy for whether a classroom is getting enough outdoor air per person. It is not a contaminant limit in itself at typical indoor levels, but steady-state readings well above about 1,000 to 1,100 ppm in an occupied classroom usually indicate under-ventilation. Several provincial health and education bodies published classroom ventilation guidance after 2020, and many boards now monitor CO2 in every classroom.

Demand-controlled ventilation with CO2 sensors works well in gyms, libraries and multipurpose rooms where occupancy is highly variable. In classrooms the benefit is smaller because they are usually either full or empty, and occupancy sensors or schedules often capture most of the savings more simply.

Acoustics

Background noise directly affects speech intelligibility, and HVAC is often the largest contributor. ANSI/ASA S12.60 sets a target of 35 dBA background noise in core learning spaces under 566 m3. Many Canadian school boards reference it in their design standards even where it is not mandatory.

Meeting it takes deliberate choices:

• Keep fan coils, heat pumps and unit ventilators out of the classroom where possible, or select them carefully for low sound power.
• Size ducts for low velocity near the room, typically 3 to 4 m/s (600 to 800 fpm) in branch ducts serving classrooms.
• Locate VAV terminals and fan-powered boxes over corridors rather than over teaching areas.
• Use lined duct, silencers or elbows between the air handler and the first classroom.
• Select diffusers for NC 25 to 30 or lower at design airflow.

Common system types

There is no single right answer. The choice depends on the age and layout of the building, whether it is new construction or a modernization, and the board's maintenance capabilities.

Dedicated outdoor air systems paired with heat recovery have become a strong default in new Canadian schools. They deliver a known quantity of outdoor air to each classroom regardless of heating demand, and the recovery wheel or plate exchanger can cut the ventilation heating load by well over half.

Heating in cold climates

Perimeter heating, whether hydronic fin-tube, radiant panels or in-floor, remains common in schools because it counters downdrafts from large windows. In-floor radiant heating is popular for kindergarten rooms where children sit and play on the floor.

Freeze protection deserves real attention. Outdoor air coils in schools sit idle with closed dampers overnight and on weekends, then open to -30 C (-22 F) air in the morning. Glycol heating loops, preheat coils with face-and-bypass dampers, or heat recovery upstream of water coils are the usual defences.

Gymnasiums, theatres and special spaces

Gyms have high ceilings, high but intermittent occupancy and loose temperature requirements. Typical approaches include dedicated air handlers with CO2-based ventilation control, radiant heating, and high-volume low-speed fans for summer comfort and destratification.

Other spaces with specific needs:

• Science labs: fume hoods need dedicated exhaust, make-up air and face velocity verification. See laboratory HVAC and fume hood exhaust.
• Shops and technical education rooms: dust collection, welding fume extraction and paint booth exhaust under provincial occupational health rules.
• Kitchens and cafeterias: commercial kitchen exhaust under NFPA 96 with make-up air.
• Server rooms and IT closets: small dedicated cooling that runs year-round, including the summer break.

Summer use and cooling

Many older Canadian schools have no cooling. With longer heat waves, rising expectations and year-round programming, boards increasingly add cooling during modernizations. Where full cooling is not affordable, options include cooling the DOAS supply air, adding cooling to libraries and gyms used as cooling refuges, and night flushing during shoulder seasons.

Cooling also matters for the building itself in summer. Unconditioned, closed-up schools can see high indoor humidity that encourages mould in carpets and storage rooms. Maintaining some dehumidification during the summer break is often worthwhile.

Controls and operations

School controls should be robust and simple. Key features include:

1. Occupancy schedules tied to the school calendar, including holidays and professional development days.
2. Optimal start so classrooms are at temperature when students arrive without running the plant all night.
3. Occupancy sensors in classrooms to reduce ventilation and relax setpoints when rooms are empty.
4. Clear graphics and alarms that a district technician can interpret remotely.
5. Open protocols such as BACnet so the board is not tied to a single vendor across its portfolio.

Testing, adjusting and balancing at turnover, followed by commissioning, catches the issues that most often cause complaints: classrooms with too little outdoor air, noisy terminals and freeze-stat trips. Schools also benefit from re-balancing after renovations, since classroom uses change over time. Our air balancing team regularly verifies classroom outdoor air quantities against design.

Frequently asked questions

Do schools in Canada have to meet ASHRAE 62.1?

Most provinces require ventilation to be designed to ASHRAE 62.1 through the building code for new construction and major renovation. Existing schools are generally evaluated against the code in force when they were built, though many boards have adopted their own higher standards. Confirm requirements with the authority having jurisdiction.

Are portable HEPA filters a substitute for ventilation?

No. Portable air cleaners reduce airborne particles, including infectious aerosols, but they do not remove CO2 or other gases or supply fresh air. They are a useful supplement where ventilation cannot easily be improved.

Key takeaways

• Classroom ventilation under ASHRAE 62.1 is substantial, so heat recovery is essential in Canadian schools.
• CO2 monitoring is a practical way to confirm classrooms are getting adequate outdoor air.
• Design for 35 dBA background noise in learning spaces by keeping equipment and high velocities away from classrooms.
• DOAS with heat recovery plus separate heating and cooling is a strong option for new and renovated schools.
• Freeze protection and simple, well-documented controls are critical for long-term reliability.
• Balancing and commissioning at turnover catch the issues that cause most classroom complaints.