👥 People vs. Area Share
👥 Airflow Per Person
Ventilation Breakdown
Full Calculation Table
| Component | Basis | Value | Result |
|---|
How to Use the Commercial Ventilation Calculator
Choose the category that best matches the zone. Each category comes with default per-person (Rp) and per-area (Ra) outdoor air rates from the ASHRAE 62.1 Ventilation Rate Procedure.
Enter the conditioned floor area of the specific zone. This drives the area-based ventilation component and, if you leave occupant count blank, the default occupancy estimate.
Enter your design occupant count if known, or leave blank to use the default occupant density for the selected category.
Click Calculate Ventilation Requirement to see the people-based component, area-based component, and total minimum outdoor airflow for the zone.
Understanding the ASHRAE 62.1 Ventilation Rate Procedure
The Ventilation Rate Procedure is the most widely used method for setting minimum outdoor air requirements in Canadian commercial buildings, adopted into provincial building and mechanical codes overseen through the National Building Code of Canada framework. It combines two separate components into a single required outdoor airflow for each zone, recognizing that ventilation needs come from both the people in a space and the space itself.
| Occupancy Category | Rp (L/s per person) | Ra (L/s per m²) |
|---|---|---|
| Office Space | 2.5 | 0.3 |
| Conference / Meeting Room | 2.5 | 0.6 |
| Retail Sales | 3.8 | 0.9 |
| Restaurant Dining | 3.8 | 0.9 |
| Classroom | 5.0 | 0.6 |
Values shown are general representative rates for common occupancy categories, intended for preliminary sizing. Confirm exact Rp and Ra values against the current edition of ASHRAE 62.1 adopted by your provincial code, since rates vary by specific occupancy subcategory.
Why Two Components Instead of One Number
A single per-person or per-area rate would either under-ventilate low-occupancy, high-area zones or over-ventilate small, densely occupied rooms. Combining a people-based component, the same per-person basis the CFM per person calculator works from, with an area-based component captures both contaminant sources: bioeffluents from occupants and off-gassing from furnishings, finishes, and building materials that exists regardless of how many people are in the room.
Zone-by-Zone Calculation, Then System-Level Combination
This calculator sizes one zone at a time, which is the correct starting point since ASHRAE 62.1 rates are defined per zone by occupancy category. For a multi-zone system serving several different occupancy types, the mechanical designer needs to calculate each zone separately, then combine them using the system-level ventilation efficiency method described in the standard. That combination step is beyond a single zone calculation and typically requires the full multi-zone worksheet from ASHRAE Standard 62.1 Appendix A.
From Ventilation Requirement to Equipment Sizing
Once you know the outdoor air requirement for a zone, that number becomes an input to downstream equipment sizing. Feed it into the AHU sizing calculator to check whether ventilation or cooling load governs supply airflow, or into the DOAS calculator if the project uses a dedicated outdoor air system separate from the recirculating AHU.
Provincial Code Amendments
Most Canadian provinces reference ASHRAE 62.1 through their building or mechanical codes, but the specific edition year and any local amendments vary. Some provinces adjust minimum rates for specific occupancy types or add requirements around demand-controlled ventilation using carbon dioxide sensors, which the CO2 level calculator can help evaluate against typical indoor thresholds. Always confirm the specific edition and any provincial modifications with your local authority having jurisdiction before finalizing a design.
Frequently Asked Questions
The Ventilation Rate Procedure adds two components together. The people-based component multiplies the design occupant count by a per-person outdoor air rate specific to the occupancy category. The area-based component multiplies floor area by a per-area outdoor air rate for that same category. The sum of both is the required zone outdoor airflow.
Different activities produce different contaminant loads and occupant densities. A densely packed conference room needs more outdoor air per person than a lightly occupied office because higher density concentrates bioeffluents faster, while an occupancy category with more equipment or furnishings off-gassing contributes to the area-based component regardless of how many people are present.
Most Canadian provinces reference ASHRAE 62.1 through their building or mechanical codes, though some provinces adopt a specific edition year or add local amendments. Always confirm the specific edition and any provincial modifications with your local authority having jurisdiction before finalizing a ventilation design, since amendments can adjust minimum rates for certain occupancy types.
Not necessarily. Outdoor air dilutes indoor contaminants, but if outdoor air itself carries high particulate or pollen loads, oversized ventilation without proper filtration can work against air quality goals. Minimum ventilation rates are a code floor for acceptable indoor air quality, not a target to maximize, and any increase above minimum should be weighed against the added heating and cooling energy needed to condition that additional outdoor air. See the energy recovery wheel calculator for ways to reduce that energy penalty.
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