The Ontario Building Code | Circuit Venting
7.5.3.1. circuit Venting
(1) A section of a horizontal branch may be circuit vented provided,
(a) a circuit vent is connected to it,
(b) all fixturesserved by the circuit vent are located in the same storey and located at the most distant upstream section of the horizontal branch, and
(c) no soilor waste stack is connected to it upstream of a circuit vented fixture.
(2) Fixtures with fixture outlet pipes less than 2 in. in size 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 soil or waste pipe having a hydraulic load not greater than six fixture units may act as a relief vent for a branch that is being circuit vented.
(5) A symmetrically connected relief vent may serve as a combined relief vent for a maximum of two branches that are circuit vented, provided there are not more than eight circuit vented fixtures connected between the combined relief vent and each circuit vent.
(6) Additional circuit vents shall be required,
(a) when 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 eight circuit vented fixtures are connected to a branch between vent pipeconnections.
(7) A soil or waste pipe may serve as an additional circuit vent in accordance with Sentence (6) provided that the soilor waste pipe is sized as a wet vent in conformance with Article 7.5.8.1. and is not less than 2 in. in size.
(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 7.4.10.8., except that it shall be not less than,
(a) 2 in., where trapsless than 2 in. in size are circuit vented, or
(b) 3 in., where traps2 in. in size 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).