A vent stack or main vent connecting relief vents, circuit vents, or loop vents shall have a diameter of at least one-half the diameter of the soil or waste stack to which the vent stack or main vent is connected, but in no case less than 1-1/2 inches. The maximum number of fixture units connected to the vent stack shall be in accordance with Table P-1110.4. The vent stack or main vent shall not be less in size than the branch, circuit, or loop vent it is servicing. Where fixtures are installed on the house drain behind the line of vent, a minimum vent stack of 1-1/2 inches shall be required for small fixtures having a fixture unit value not greater than 10 and a minimum of 2 inches for one or more water closets and other fixtures, except if a larger size is required according to Table P-1110.4.
The diameter of a relief vent shall not be less than one-half the diameter of the horizontal branch to which it is connected, with a minimum size of 1-1/2 inches. The maximum number of fixture units connected to the relief vent shall be in accordance with Table P-1110.4.
|Diameter of Vent (inches) — Maximum Length of Vent (feet)|