Canadian building code question

What are the building code requirements for makeup air and HRV systems in Canada?

Makeup air is required whenever exhaust systems create negative pressure that could affect combustion appliances, building envelope performance, or occupant comfort. HRV/ERV systems are increasingly required or incentivized under energy codes to recover heat from exhaust air in tightly sealed buildings.

Modern building envelopes are tight enough that exhaust fans, range hoods, and dryers can depressurize a building and cause backdrafting of combustion appliances. The code requires makeup air to compensate. Heat recovery ventilators and energy recovery ventilators are the preferred method in energy-efficient buildings because they satisfy ventilation requirements while recovering heat.

What to check first

  • Determine the total exhaust capacity of all fans and appliances to calculate the required makeup air volume.
  • Check whether the energy code or provincial code requires or incentivizes heat recovery ventilation for the building type and climate zone.
  • Verify that the ventilation system design prevents negative pressure that could cause backdrafting of combustion appliances.

Jurisdiction notes

National baseline

The NBC and referenced CSA F326 require adequate ventilation in residential buildings. Makeup air requirements are triggered by exhaust capacity and the presence of fuel-burning appliances.

Energy code

The National Energy Code and provincial energy codes increasingly require or incentivize HRV/ERV systems in new construction to meet ventilation and energy performance targets.

Provincial variation

BC Step Code, Ontario SB-12, and Quebec energy regulations each have specific provisions that affect when HRV systems are required versus optional.

Work through it in this order

  1. Calculate the total exhaust capacity from range hoods, bathroom fans, dryers, and other exhaust appliances.
  2. Determine the makeup air volume required to prevent depressurization below the threshold that affects combustion appliances.
  3. Check the energy code for HRV/ERV requirements based on the building type, climate zone, and airtightness target.
  4. Design the ventilation system to balance supply and exhaust while meeting the minimum ventilation rates from CSA F326 or the applicable standard.

Common questions

Is an HRV required in all new homes in Canada?

Not universally by the NBC, but many provinces effectively require them through energy code performance targets. Check the applicable provincial energy code and airtightness requirements.

When does a range hood require makeup air?

Generally, when the range hood exhaust capacity exceeds approximately 75-150 CFM (depending on jurisdiction), dedicated makeup air is required to prevent depressurization.

Can an HRV replace a bathroom exhaust fan?

An HRV can serve as the exhaust source for bathrooms if the system is designed to provide the required exhaust airflow rate at each location. Consult the mechanical designer and local code.