PART 7 — PLUMBINGUpdated for the 2024 Ontario Building Code
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7.5.3.1.Circuit Venting
(1) A section of horizontal branch may be circuit-vented provided
(a) a circuit vent is connected to it,
(b) all fixtures served by the circuit vent are located in the same storey,
(c) no stack is connected to it upstream of a circuit-vented fixture.
(2) Fixtures with fixture outlet pipes less than NPS 2 shall be separately vented or separately circuit-vented.
(3) Except as provided in Sentences (4) and (5), a relief vent shall be connected to the branch that forms part of a
circuit-vented system, downstream of the connection of the most downstream circuit-vented fixture.
(4) A sanitary drainage pipe having a hydraulic load not greater than 6 fixture units is permitted to act as a relief vent for
a branch that is circuit-vented.
(5) A symmetrically connected relief vent is permitted to serve as a combined relief vent for a maximum of 2 branches
that are circuit-vented, provided there are not more than 8 circuit-vented fixtures connected between the combined relief
vent and each circuit vent.
(6) Additional circuit vents shall be required
(a) where each cumulative horizontal change in direction of a branch served by a circuit vent exceeds 45° between vent
pipe connections, or
(b) where more than 8 circuit-vented fixtures are connected to a branch between vent pipe connections.
(7) A sanitary drainage pipe is permitted to serve as an additional circuit vent in accordance with Sentence (6),
provided the sanitary drainage pipe is sized as a wet vent in conformance with Article 7.5.8.1. and is not less than NPS 2.
(8) Connections to circuit vents and additional circuit vents in accordance with Sentence (6) shall conform to Sentence
7.5.4.5.(1).
(9) A circuit-vented branch, including the fixture drain downstream of the circuit vent connection, shall be sized in
accordance with Articles 7.4.10.7. and 7.10.4.8., except that it shall be not less than
(a) NPS 2, where traps less than NPS 2 are circuit-vented, or
(b) NPS 3, where traps of NPS 2 or larger are circuit-vented.
(10) Additional circuit vents shall be sized in accordance with Table 7.5.7.1. and Sentence 7.5.7.3.(1).
(11) The hydraulic load on a circuit vent shall include the hydraulic load from fixtures connected to the branch served by
the circuit vent, but shall not include the hydraulic load from fixtures permitted by Sentences (3), (4) and (5).
This provision includes a table — formatting is preserved from the source; refer to the official code for the authoritative layout.
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Code text is reproduced for reference from the Ontario Building Code (O. Reg. 163/24, 2024 Building Code Compendium). This page is provided for general information and is not an official copy. Always verify requirements against the official Ontario Building Code and confirm with your local building department.