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Ventilation rate requirements for Canadian buildings
As Canadian homes and buildings have become significantly more airtight under updated National Building Code requirements, mechanical ventilation has shifted from optional to mandatory. Air that once leaked through gaps and cracks now has to be deliberately brought in and exhausted, or indoor air quality suffers from accumulated moisture, CO2, and pollutants from cooking, cleaning, and off-gassing materials.
ASHRAE 62.2 governs low-rise residential buildings (houses, townhouses, and small multi-family buildings up to 3 storeys). ASHRAE 62.1 governs everything else: offices, schools, retail, restaurants, and larger multi-family buildings. Both standards aim for the same outcome — sufficient outdoor air to maintain acceptable indoor air quality — but use different calculation methods suited to their respective building types.
The ASHRAE 62.2 whole-building formula
The current ASHRAE 62.2 formula is Qfan = 0.03 × Afloor + 7.5 × (Nbr + 1), where Afloor is conditioned floor area in square feet and Nbr is the number of bedrooms (a studio counts as 0). This gives a continuous CFM requirement. If your ventilation system runs intermittently rather than continuously, ASHRAE 62.2 provides a run-time factor that increases the required instantaneous rate to compensate — a system running 6 hours per day needs roughly 4 times the continuous rate during its operating window.
Most Canadian homes built to current code meet this requirement through a continuously or intermittently operating HRV (Heat Recovery Ventilator) tied into the forced-air distribution system, supplemented by local exhaust fans in kitchens and bathrooms for spot ventilation during moisture and odour-generating activities.
The ASHRAE 62.1 Ventilation Rate Procedure
Commercial spaces use a 2-part calculation: a people-based component (Rp × occupancy) plus an area-based component (Ra × floor area), divided by the zone air distribution effectiveness (Ez). Different space types have different Rp and Ra values reflecting their typical pollutant generation — a gym needs much more outdoor air per person than a quiet office due to higher metabolic rates and activity levels. This calculator includes the most common Table 6-1 values; always verify against the current ASHRAE 62.1 edition adopted by your local building code for final design.
For multi-zone systems, the building-level outdoor air requirement involves additional system ventilation efficiency calculations beyond a single zone's requirement. Use the outdoor air calculator for multi-zone system-level analysis.
Frequently Asked Questions
Qfan = 0.03 × Afloor + 7.5 × (Nbr + 1), in CFM, where Afloor is conditioned floor area in ft² and Nbr is bedroom count. For a 2,000 sq ft home with 3 bedrooms: 0.03×2000 + 7.5×4 = 60+30 = 90 CFM continuous. This can be provided continuously or intermittently with a higher instantaneous rate per the run-time factor table. Most Canadian homes meet this through an HRV or ERV integrated with the forced-air system. Use the HRV calculator to size the unit.
ASHRAE 62.1 covers commercial, institutional, and multi-family buildings using the Ventilation Rate Procedure with people-based and area-based rates by space type. ASHRAE 62.2 covers low-rise residential buildings (single-family, small multi-family up to 3 storeys) using a simpler whole-building formula plus local exhaust requirements. A duplex or rowhouse typically follows 62.2; an apartment building, office, or school follows 62.1. Use the mode tabs above to switch between calculations.