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Drain Pipes and Vent Stack

Drain pipes and vent stack sizing

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Vents transports sewer gas through the building to open air space. Properly installed the vents prevents traps siphoning and sewage gas to leak into the interior building.

Different codes in different jurisdictions exists and must be adhered to locally. In general we talk about

  • individual vents
  • relief vents
  • circuit vents
  • branch vents
  • stack vents

Individual vents

Individual vents serve individual fixtures.

Sewage vent - individual

This vents only one fixture but may connect into an other vent that extends to open air.

  • an individual vent should be at least one-half the size of the drain it vents (no less than 1 1/4", 32 mm)

Relief vents

Relief vents provide additional air to the drainage system where the primary vent is too far from the fixture.

Sewage vent - relief


  • an relief vent should be at least one-half the size of the drain it vents (no less than 1 1/4", 32 mm)

Circuit vents

Circuit vents are used with more than one fixtures. A circuit vent is installed before the last fixture extend up to open air or connects to an other vent that extend to the outside

Sewage vent - circuit

  • an circuit vent should be at least one-half the size of the drain it vents (no less than 1 1/4", 32 mm)

Branch vents

Branch vents are vents extending horizontally that connects multiple vents together.

Sewage vent - branch

Stack vents

A vent stack is used only for the purpose of venting.

Sewage vent - soil stack

Vents are normally sized by using the "Developed Length" (total linear footage of pipe making up the vent) method.

Maximum length of vent stacks and relief vents

Maximum length of vent stacks and relief vents (ft)
Size of Soil Waste Stack
Fixture Units ConnectedDiameter of Required Vent Stack (in)
1 1/41 1/222 1/2345
1 1/4 2 30
1 1/2 8 50 150
10 30 100
2 12 30 75 200
20 26 50 150
2 1/2 42 30 100 300

10 30 100 200 600
30 60 200 500
60 50 80 400

100 35 100 260 1000
200 30 90 250 900
500 20 70 180 700

200 35 80 350 1000
500 30 70 300 900
1100 20 50 200 700
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Related Topics

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Tag Search

  • en: vents drain sewage
  • es: rejillas de drenaje de aguas cloacales
  • de: Öffnungen abfließen Abwasser
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