Drainage Vents

Reference data and engineering information about drainage vents for piping systems applications.

drainagevents

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

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Maximum length (ft) of vent stacks and relief vents based on stack size, fixture units, and vent diameter
Stack Size(in)	Fixture Units	Vent Ø 1¼ in(ft)	Vent Ø 1½ in(ft)	Vent Ø 2 in(ft)	Vent Ø 2½ in(ft)	Vent Ø 3 in(ft)	Vent Ø 4 in(ft)	Vent Ø 5 in(ft)
1¼	2	30	—	—	—	—	—	—
1½	8	50	150	—	—	—	—	—
1½	10	30	100	—	—	—	—	—
2	12	30	75	200	—	—	—	—
2	20	26	50	150	—	—	—	—
2½	42	—	30	100	300	—	—	—
3	10	—	30	100	200	600	—	—
3	100	—	30	60	200	500	—	—
3	500	—	—	50	80	400	—	—
4	35	—	—	100	260	1000	—	—
4	200	—	—	30	90	900	500	—
4	500	—	—	20	70	700	—	—
5	200	—	—	—	35	80	350	1000
5	500	—	—	—	30	70	300	900
5	1100	—	—	—	20	50	200	700

Source: engineeringtoolbox.com

Approved Drainage and Vent Pipe Materials

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Approved piping materials for drainage and vent systems per U.S. standards
Piping Material	US Standards
ABS plastic pipe (IPS diameters, Schedule 40, DR 22, DR 24)	ASTM D2661; ASTM F628; ASTM F1488; CSA B181.1
Cast-iron pipe	ASTM A74; ASTM A888; CISPI 301
Copper or copper-alloy pipe	ASTM B42; ASTM B43; ASTM B302
Copper or copper-alloy tubing (Type K, L, M, DWV)	ASTM B75; ASTM B88; ASTM B251; ASTM B306
Galvanized steel pipe	ASTM A53
Glass pipe	ASTM C1053
Polyolefin pipe	ASTM F1412; CSA B181.3
PVC plastic pipe (IPS diameters, Schedule 40, DR 22, DR 24)	ASTM D2665; ASTM F891; ASTM F1488; CSA B181.2
PVC plastic pipe (3.25-inch O.D.)	ASTM D2949; ASTM F1488
PVDF plastic pipe	ASTM F1673; CSA B181.3
Stainless steel (Types 304 & 316L)	ASME A112.3.1

Source: engineeringtoolbox.com

Interactive Charts

Sewage vent - individual

References

Original Source

Source: engineeringtoolbox.com