Short answer: the 2024 Ontario Building Code (O. Reg. 163/24) took effect on January 1, 2025, and every permit application made since April 1, 2025 must follow it.[1] For ventilation, it references ASHRAE Standard 62.1-2016 instead of the 2010 edition used by the 2012 OBC.[2] The outdoor air your mechanical engineer designs to is therefore based on the 2016 edition, and a TAB (air balance) report is the field document that shows what the system actually delivers.
What changed in the 2024 Ontario Building Code for ventilation?
The 2024 OBC is harmonized with the 2020 National Building Code, which eliminated about 1,730 technical variations between the provincial and national requirements.[1] The transition was short: permits could still be filed under the 2012 OBC until March 31, 2025 if working drawings were substantially complete before January 1, 2025; from April 1, 2025, all applications use the 2024 code.[1]
For Part 6 (HVAC) buildings, the changes that matter most to air balancing are:[3]
- Referenced edition: ASHRAE 62.1-2016 replaces 62.1-2010 (the 2020 NBC also references the 2016 edition).
- Sentence 6.3.1.1.(2): expanded outdoor air supply requirements with three design options, each tied to specific sections of ASHRAE 62.1.
- New Sentence 6.3.1.1.(3): exhaust ventilation must be provided in accordance with Section 6.5 of ASHRAE 62.1.
- New Sentence 6.3.1.1.(4): introduces the term "heating-season mechanical ventilation".
- Clause 6.2.1.1.(1)(j): ASHRAE Guideline 12 is now cited as good engineering practice to minimize the risk of legionella.
- Article 6.3.2.2.: drain pans are required for all HVAC systems that generate condensate or add liquid water to the airstream.
Note that a newer edition, ASHRAE 62.1-2025, has been published.[7] The Ontario code still points to the 2016 edition, so a design may legitimately differ from the latest ASHRAE tables.
Does ASHRAE 62.1-2016 still cover apartment buildings?
Not for the dwelling units. The 2016 edition removed residential occupancies from its scope: units with non-transient occupants (more than 30 days) fall under ASHRAE 62.2, while common areas such as corridors and amenity rooms stay under 62.1. Previously, 62.1 applied to multi-unit residential buildings of four storeys or more.[2]
The catch: the OBC does not list ASHRAE 62.2 among its referenced standards. The City of Kitchener has said it will accept ASHRAE 62.2-2016 as good engineering practice until the code is amended.[2] We have not found a published position from the City of Ottawa on this point, so on Part 3 residential projects in Ottawa, confirm the basis of design with the engineer of record and Building Code Services before the TAB scope is priced.
What does ASHRAE 62.1 ask of air balancing?
Section 7.2.2 of ASHRAE 62.1 (Air Balancing) requires ventilation systems to be balanced in accordance with ASHRAE Standard 111 or other applicable national standards, so as to verify conformance with the standard's total outdoor airflow requirement (Vot).[5] In practice, AABC and NEBB procedures are the national standards TAB firms in Canada use for this.
Two cautions. First, the exact wording of 7.2.2 was revised by addenda to the 2016 edition (including whether direct measurement is required), so check the version the specification calls up.[5] Second, we have not confirmed whether the OBC's references to ASHRAE 62.1 extend to Section 7. Whether a TAB report is mandatory on your project usually comes from the mechanical specification, the engineer's general review and the municipality, not from the code alone.
How is the required outdoor airflow calculated?
The Ventilation Rate Procedure adds a people component and an area component: Vbz = Rp × Pz + Ra × Az. The zone outdoor airflow is then Voz = Vbz / Ez, where Ez is the zone air distribution effectiveness (for example 1.0 for ceiling supply of cool air, 0.8 for ceiling supply of warm air at least 8 °C (15 °F) above space temperature with a ceiling return). For a single-zone unit, the outdoor air intake equals Voz.[6]
Illustration only, using office-type rates of 5 cfm/person and 0.06 cfm/ft²[6] for a 2,000 ft² (186 m²) space designed for 20 people and served by a rooftop unit in heating mode:
- People: 20 × 5 = 100 cfm (47 L/s)
- Area: 2,000 × 0.06 = 120 cfm (57 L/s)
- Vbz = 220 cfm (104 L/s)
- Voz = 220 / 0.8 ≈ 275 cfm (130 L/s) of outdoor air at the unit's minimum position
The real rates for each occupancy are in Table 6.2.2.1 of the edition referenced by the code, and the design value is the engineer's. The TAB firm does not redesign; it measures and reports against the scheduled minimum outdoor air.
How is outdoor air measured in the field?
- Pitot-tube traverse of the outdoor air duct — the preferred method where a straight duct section exists, with the economizer held at minimum position.
- Airflow measuring station — when installed, its reading is verified against a traverse before it is relied on.
- Mixed-air temperature method — % outdoor air = (Treturn − Tmixed) / (Treturn − Toutdoor). Indirect, and unreliable when the indoor–outdoor temperature difference is small or the air does not mix well.
- Total supply minus return — a cross-check only, since duct leakage and measurement error add up.
Outdoor air ducts often run at low velocity, which makes them hard to read. For standard air, velocity pressure is (V / 4005)² in in. w.g. with V in fpm: at 600 fpm (3.0 m/s) that is only about 0.022 in. w.g. (5.6 Pa), and at 400 fpm (2.0 m/s) about 0.010 in. w.g. (2.5 Pa). Readings this small need a calibrated micromanometer and a proper traverse grid; a single-point reading is not enough.
What should an outdoor air verification report include?
- Design and measured minimum outdoor air for each unit, in CFM and L/s, with % of design
- Total supply, return and exhaust airflow, and the operating mode during the test (occupied, economizer at minimum, VAV position)
- Fan data: RPM, motor amperage and voltage, external static pressure in in. w.g. and Pa
- Outdoor and return air temperatures at the time of testing
- Measurement method, traverse location and instrument calibration dates
- Deficiencies: damper not responding, BAS minimum set incorrectly, dirty filters, missing access, system not complete
To avoid a costly return visit, make sure before the TAB visit that the units run in occupied mode, the controls contractor can set the economizer to minimum, filters are new and ceiling access is available.
What about projects in Gatineau?
Projects on the Quebec side are governed by the Quebec Construction Code, not the OBC, and its referenced editions can differ. This article covers Ontario only; for Gatineau and the Outaouais, confirm the applicable code with the designer.
Need outdoor air verified on an Ottawa project?
GreenTech Air Balancing measures outdoor, supply, return and exhaust airflow on commercial units, restaurants, clinics and tenant fit-outs, and documents the results in a TAB report for the engineer, owner and inspector. See our air balance report for occupancy page, or send us your mechanical drawings for a fixed price.
This article is general information, not legal or engineering advice. TAB field measurements document system performance at the time of testing; final design and code compliance remain the responsibility of the design professional, the owner and the authority having jurisdiction.
Frequently asked questions
Sources
- HRAI — New Year, New Building Code (2024 OBC effective dates and harmonization with the 2020 NBC)
- City of Kitchener — Building Bulletin BB 2025-09, Mechanical Ventilation for Part 3 Residential Buildings (ASHRAE 62.1 and 62.2), Oct. 22, 2025
- Town of Tillsonburg — 2024 OBC Division B Part 6 (HVAC) changes, slide deck
- Government of Ontario — O. Reg. 163/24: Building Code (e-Laws)
- ASHRAE — Addendum q to Standard 62.1-2016 (Section 7.2.2, Air Balancing and Verification of Outdoor Air Performance)
- D. Stanke, "Addendum 62n: Single-Zone & Dedicated-OA Systems", ASHRAE Journal, Oct. 2004 (Ventilation Rate Procedure equation and Ez table)
- ANSI Blog — ANSI/ASHRAE 62.1-2025: Ventilation and Acceptable Indoor Air Quality
