Maximum length of horizontal vent pipe


Old 11-21-19, 10:14 AM
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Maximum length of horizontal vent pipe

I need to relocate a 2 inch vent pipe that interferes with my new solar array on my roof. How many feet can I run the vent pipe horizontally in the attic prior to going vertical through the roof. Second question is: how often (feet) should the pipe be secured to a non-moving surface?
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Old 11-21-19, 10:27 AM
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I don't know if there is a code requirement, but one of my 2" vent lines ran about 20' horizontally before it penetrated the roof.
Old 11-21-19, 10:37 AM
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I would not run a vent pipe horizontally.

It should have some slope to it (about 1/8 to 1/4 inch per foot)

It should be supported enough so it cannot sag so it depends on what the vent is made of. As a guess I would say every 4 feet.
Old 11-21-19, 04:09 PM
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I don't know of a limit on vent pipe length. As manden mentioned it should be sloped the same as any other drain line so it doesn't collect water.
Old 11-21-19, 10:04 PM
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The rule of thumb that I've used it that the vent can't be more than 1/3 horizontal. And pitched is good.
Old 11-22-19, 02:44 PM
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There's no code that specifies a maximum horizontal run as long as you maintain a standard 1/4" (or 1/8" if needed) slope.

PVC pipe needs to be supported every 4'. I would use either the plastic J-hooks, or plumbers tape (metal or plastic 3/4" wide tape with holes every inch or so).
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