Drainage Vents

Overview

Engineering reference data for Drainage Vents in piping systems.

Key Formulas

Continuity

$A_1 v_1 = A_2 v_2$

Mass conservation in pipe flow.

Pressure Drop

$\Delta P = f \frac{L}{D} \frac{\rho v^2}{2}$

Darcy-Weisbach equation.

Pipe Area

$A = \frac{\pi D^2}{4}$

Cross-sectional area of a pipe.

Variables

Symbol	Description	Unit
$D$	Pipe diameter	m
$v$	Flow velocity	m/s
$\Delta P$	Pressure drop	Pa
$f$	Friction factor	—

Vent Types and Applications

Different vent configurations serve specific purposes in drainage systems:

Vent Type	Description	Application
Individual Vents	Serve a single fixture	May connect to another vent extending to open air
Relief Vents	Provide additional air to the drainage system	Required when primary vent is too far from fixture
Circuit Vents	Serve multiple fixtures	Installed before the last fixture, extends to open air or connects to another vent
Branch Vents	Extend horizontally	Connect multiple vents together
Stack Vents	Used solely for venting purposes	Extend vertically through the building

Vent Sizing Requirements

Standard vent sizing rules:

• Individual vents: Minimum one-half the diameter of the drain served (no less than 1¼" / 32 mm)
• Relief vents: Minimum one-half the diameter of the drain served (no less than 1¼" / 32 mm)
• Circuit vents: Minimum one-half the diameter of the drain served (no less than 1¼" / 32 mm)

Vents are typically sized using the Developed Length method, which measures the total linear footage of pipe comprising the vent system.

Maximum Length of Vent Stacks and Relief Vents

Approved Drainage and Vent Pipe Materials

Interactive Charts

References

• Original Source