⚖ Occupancy Share of Total
📐 Outdoor Air Per Person
Requirement Breakdown
Full Calculation Table
| Component | Rate | Quantity | Airflow |
|---|
How to Use the ASHRAE 62.1 Calculator
Pick the space type closest to your zone. Each category loads the default people and area outdoor air rates from ASHRAE 62.1 Table 6-1. Pick Other / Custom if you already have project-specific Rp and Ra values.
Enter the zone floor area and the design occupant count. Use the actual expected population, not the building's egress capacity, unless your jurisdiction requires otherwise.
Choose the supply and return configuration that matches your design. Ceiling supply and return of cool air gets full credit. Warm-air ceiling supply during heating often needs a lower Ez.
Click Calculate Outdoor Air to see the breathing zone airflow (Vbz), the zone outdoor airflow (Voz) your system has to deliver, and a breakdown of what is driving the number.
Understanding the ASHRAE 62.1 Ventilation Rate Procedure
The Ventilation Rate Procedure in ASHRAE Standard 62.1 is the most common way to size outdoor air for commercial buildings in Canada. It starts with the breathing zone, which is the occupied volume of a room from about 75 mm to 1.8 m above the floor. The standard sets two minimum airflow components for every zone, and a designer adds them together rather than choosing one or the other.
Rp and Ra: Two Different Contaminant Sources
The people outdoor air rate, Rp, addresses contaminants that come from occupants themselves, mainly carbon dioxide and body odour. It scales with how many people are in the room. The area outdoor air rate, Ra, addresses contaminants that come from the building, including off-gassing from carpet, furniture, and finishes. It scales with floor area regardless of occupancy. A nearly empty conference room still needs area-based ventilation, and a packed one needs both. Our CFM per person calculator isolates just the people-based piece if that is all you need.
The Example button shows the arithmetic. A 120 m² office with 18 occupants uses Rp 2.5 L/s per person and Ra 0.3 L/s per m², so Vbz = (2.5 × 18) + (0.3 × 120) = 45 + 36 = 81 L/s, about 172 CFM. With Ez at 1.0, Voz is also 81 L/s, or 4.5 L/s per person.
Zone Air Distribution Effectiveness
Vbz tells you what has to reach the breathing zone, but real air distribution isn't perfect. Ez corrects for that. A well-mixed system with ceiling supply and return of cool air gets full credit at 1.0. Warm supply air from the ceiling tends to stay near the ceiling during heating season, which can drop Ez to 0.8 and means the air handler has to move more outdoor air to hit the same target. Run the same office in heating mode at Ez 0.8 and Voz becomes 81 ÷ 0.8 = 101.3 L/s, about 215 CFM, which is 25% more outdoor air for the same room. This is one reason Canadian commercial buildings often need careful heating-mode airflow checks, not just a single annual design value.
Why This Matters for Equipment Sizing
Once you know Voz, that airflow becomes a real heating and cooling load on the system. Bringing in more outdoor air in a Calgary or Winnipeg winter means a larger preheat coil or a properly sized heat recovery unit. Use the ventilation heat load calculator to convert this airflow into a load, then size recovery equipment with the HRV calculator or ERV calculator. If the outdoor air will be handled by its own unit instead of the main air handler, the DOAS calculator estimates the coil loads for a dedicated outdoor air system sized to this Voz.
Single-Zone vs. Multi-Zone Systems
This calculator handles a single zone, which is the right scope for most small commercial spaces and for checking individual rooms in a larger building. Multi-zone recirculating systems need an additional system-level calculation that applies a system ventilation efficiency, Ev, to account for how outdoor air is shared across zones, which is outside this tool's scope. The ASHRAE 62.1 compliance calculator takes an Ev value for multi-zone work, and a mechanical engineer typically runs and stamps the full system calculation for permit.
Demand-Controlled Ventilation
Spaces with occupancy that varies a lot through the day, like classrooms, gyms, and conference rooms, are good candidates for demand-controlled ventilation. Instead of supplying the full design Voz continuously, a CO2 sensor lets the system reduce outdoor air when the room is lightly occupied. Our demand-controlled ventilation calculator estimates the energy savings, and the CO2 calculator checks indoor concentration against the limit.
A Note on Accuracy
This calculator is an estimating tool that uses the SI default Rp and Ra values published in Table 6-1 for typical occupancy categories. ASHRAE periodically revises that table through addenda, and the National Building Code of Canada, published by the National Research Council, only becomes law once a province or territory adopts it, usually with its own amendments. For permit-stamped designs, confirm the exact rates against the edition of ASHRAE 62.1 adopted in your jurisdiction, or have a mechanical engineer verify the calculation.
Frequently Asked Questions
The Ventilation Rate Procedure (VRP) is the prescriptive method in ASHRAE 62.1 for determining minimum outdoor air in commercial buildings. It combines a per-person component (Rp) for occupant-generated contaminants and a per-area component (Ra) for building-generated contaminants, then adjusts the total for how effectively the supply air reaches the breathing zone. The result is the zone outdoor airflow, Voz, which the ventilation system must deliver. See the ventilation rate calculator for a simplified version of this check.
Rp is the outdoor airflow required per person, in L/s per person, and it covers contaminants and odours from occupants such as carbon dioxide. Ra is the outdoor airflow required per unit of floor area, in L/s per square metre, and it covers contaminants from the building itself, including furnishings, finishes, and off-gassing materials. ASHRAE 62.1 Table 6-1 lists default Rp and Ra values for dozens of occupancy categories, and both components apply to every zone. The CFM per person calculator looks at the Rp side on its own.
Ez describes how well the supply air pattern actually ventilates the breathing zone, which is roughly the occupied space from floor level to head height. A typical ceiling supply and ceiling return of cool air gets full credit at Ez 1.0. Ceiling supply of warm air during heating can stratify and drop to Ez 0.8, which means the system has to deliver more outdoor air to meet the same breathing zone target. Only low-velocity displacement systems that achieve unidirectional, stratified flow can credit a value above 1.0, typically 1.2.
Canada's National Building Code references ASHRAE 62.1 for outdoor air rates in non-residential buildings, and provinces adopt it through their own building codes, often with local amendments. Houses and small buildings under Part 9 of the code follow its own ventilation requirements in Section 9.32, which allow CSA F326 as a design route, instead of 62.1. See our whole-house ventilation calculator for the residential side. Always confirm the exact edition and any provincial amendments that apply to your project with the authority having jurisdiction.
Related HVAC Tools
Simplified 62.1 / 62.2 check
Rp-only quick lookup
CO2-based savings estimate
Check indoor concentration
Recover ventilation heat
Recover heat and moisture
Convert Voz to a load
Compare to the IAQ Procedure