Plumbing 5 Vent Systems

Sanitary Science As Applied to Buildings

Vent System

Purpose of Vents:

• Pressure Balance: Vents allow air entry to balance pressure within the plumbing system.
• Trap Seal Protection: They protect the trap seal by permitting air admission or emission, ensuring the pressure does not exceed 1 inch of water column (249 Pa).
• Sewer Gas Management: Vents help in the discharge of sewer gases, including toxic (e.g., hydrogen sulfide, ammonia) and non-toxic gases (e.g., methane, carbon dioxide).
• Trap Seal Primer: Used to compensate for water loss in traps due to evaporation.

Circuit Venting

• A vent connecting to a horizontal drainage branch, venting two to eight traps connected in a battery.
  • The location is between two most upstream fixture drains.

*Minimum slope of horizontal drain: 3%.

*Relief vent: Provided with 4 or more water closets.

• Important dimensions: $1 \text{ inch} = 25.4 \text{ mm}$.

Individual Vent / Back Vent

• A pipe installed to vent a fixture trap, connecting with the vent system above the fixture or terminating in open air.

Stack Vent

• The extension of a soil or waste stack above the highest horizontal drain connected to the stack.

Stack Venting

• A method of venting fixtures through the soil or waste stack.

Vent Stack

• A vertical vent pipe installed for air circulation to and from any part of the drainage system.

Dry Vent

• A vent that does not carry liquid or water-borne wastes.

Wet Vent

• A vent pipe section through which wastewater also flows.

Sizing Conventional Venting Systems

• Individual Vent Size: Minimum size is one-half the required drain size.
• Vent Stacks and Stack Vents Size: Minimum size is one-half the size of the drain served.
• The developed length of individual, branch, circuit, and relief vents shall be measured from the farthest point of vent connection to the drainage system to the point of connection to the vent stack, stack vent, or termination outside of the building.

Vents Required

• Each trap shall be protected against siphonage and back-pressure through venting.
• Trap Seal Protection: Vent system designed to prevent a trap seal from being exposed to a pressure differential that exceed 1 inch of a water column on the outlet side of the trap.

Vents Not Required

1. On interceptor acts as a primary settling tank and discharges through a horizontal indirect waste pipe into a secondary interceptor. The second interceptor shall be properly trapped and vented.
2. Traps serving sinks that are part of the equipment of bars, soda fountains, and counters need not be vented when location and construction make it impossible to do so. Such sink shall discharge by means of an approved indirect waste pipe into a floor sink or other approved type receptor.

Materials

• Galvanized steel or 304 stainless steel pipe should not be used underground and should be kept at least 150mm above ground.
• ABS and PVC DWV piping installations shall be installed in accordance with IS 5, IS 9 and Chapter 15 "Firestop Protection for DWV and Stormwater Application". Except for individual single family dwelling units.
• Copper tube for underground or above ground drainage and vent piping shall have a weight of not less than that of copper drainage tube type DWV.
• Copper tube shall not be used for chemical or industrial waste.
• Hard drawn copper tubing, shall be marked, tubing color shall be: Type K-green, Type L-blue, Type M-red, Type DWV-yellow
• No such pipe shall be strained or bent. Burred ends shall be reamed to the full bore of the pipe.

Size of Vents

• Shall not be less than $1-\frac{1}{4}$ (32mm) nor less than $\frac{1}{2}$ the diameter of the drain to which it is connected.
• Determined from its length and the total number of fixture units connected.
• Connection to public sewer or private disposal field shall be vented by means of one or more vent pipe, the aggregate cross sectional area of which shall not be less than the largest required building sewer.
• No more than $\frac{1}{3}$ of total permitted length, per Table 7-5, of any minimum sized vent shall be installed in horizontal position.
• When a minimum-sized vent is increased (1) pipe size for its entire length, the maximum length limitation does not apply

Vent Pipe Grades and Connections

• Vent and branch vent pipes shall be free from drops or sags, graded to drop back by gravity to the drainage pipe it serves.
• Vents connecting to a horizontal drainage pipe shall have their invert taken off above the drainage centerline of such pipe, downstream of the trap.
• Each vent shall rise vertically to at least 150mm above the flood level rim of the fixture before offsetting horizontally.
• Vents shall extend undiminished in size above the roof or be reconnected with a soil or waste vent of proper size.
• The vent pipe opening from a soil or waste pipe, except for water closets and similar fixtures, shall not be below the weir of the trap.
• Two fixtures can be served by a common vertical pipe when each wastes separately into an approved double fitting with inlet openings at the same level.

Vent Termination

Each vent pipe or stack shall:

• Extend through flashing all around the stack.
• Terminate vertically not less than 150mm above the roof.
• Have a clearance of 300mm away from any nearby vertical surface.

Each vent opening shall:

• Not terminate less than 3m from or at least 0.9m above any operable window, door opening, air intake, or vent shaft.
• Be at least 0.9 m away from any lot line, alley, and street boundary lines.
  *Vents within 3m of any part of the roof that is used for such other purposes shall extend not less than 2.1m above such roof.

*Flag poling of vents shall be prohibited.

*Vent pipes for outdoor installations shall extend not less than 3m above the surrounding ground and shall be securely supported.

*Joints at the roof around vent pipes shall be made water-tight by use of flashing material.

Distance of Trap from Vent

Vent Stacks & Relief Vents

• Each soil or waste stack extending ten (10) or more stories above the building drain shall be served by a parallel vent stack which shall extend undiminished in size from its upper terminal at roof and connect to the soil or waste stack at ground level and every fifth floor level with a "yoke vent" at a point below the horizontal soil or waste branch connection to the stack and at the nearby vent stack above the same floor to provide a relief vent.
• The size of yoke vent shall be not less in diameter than either the soil stack or the vent stack, whichever is smaller.
• The yoke vent connection at the vent stack shall be placed 1.0m above the floor level and, by means of a wye branch at the soil stack, shall be placed below the lowest drainage branch serving that floor.

Wet Venting

Vertical Wet Venting:

• Limited to vertical drainage piping receiving discharge from the trap arm of 1 and 2 fixture unit fixtures that also serves as a vent not exceeding 4 fixtures.
• Wet-vented fixtures shall be within the same story.
• No wet vet shall exceed 1.8m in developed length.
• The vertical piping between any 2 consecutive inlet levels shall be considered a wet-vented section.
• Shall not be less than 1 pipe size exceeding the required minimum waste pipe size of the upper fixture or
• Shall not be less than 1 pipe size for the sum of the fixture units served by such wet-vented section, whichever is larger, but in no case less than 2".

Vent Connection

• Common vent sizing shall be the sum of the fixtures units served but in no case smaller than the minimum vent pipe size required.

Horizontal Wet Venting for Bathroom Groups

• 1 or 2 bathroom groups located on the same floor level and for private use shall be permitted to wet vented.
• Wet vet shall be considered the vent for the fixtures and shall extend from the connection of dry vent.
• Each wet-vented fixture or trap arm shall connect independently to the wet-vented horizontal branch drain.
• Only the fixture within the bathroom groups shall connect to the wet-vented horizontal branch drain.
• The water closet fixture or trap arm connection to the wet vent shall be downstream of any fixture drain or trap arm connections.
• Any additional fixtures shall discharge downstream of the wet vent system and conventionally vented.
• The dry vent connection to the wet vent shall be an individual vet or common vent for lavatory, urinal, bidet, shower, or bathtub.
• Only one wet-vented fixture drain or trap arm shall discharge upstream of the dry-vented fixture drain connection.
• 2" diameter 4 dfu
• 3" diameter-5 dfu -12 dfu
• Dry vent shall be sized based on the total fixtures units discharging into the wet vent.

Special Venting for Island Fixtures

• Traps for island sinks and similar equipment shall be roughed in above floor
• Vented not less than the drain board height and returning it downward and connects to the horizontal drain immediately downstream from vertical fixture drain.
• The return vent shall be connected to the horizontal drain using a wye-branch fitting and provided with a foot vent by means of wye branch below the floor.
• Connect to other vents at a point not less than 6" above flood level rim of fixture being served.
• Drainage fittings shall be used on all parts of the vent below and a slope not less than $\frac{1}{4}$ inch per foot back to the drain shall be maintained.
• Return bend assembly: 45 degree, 90 degree, 45 degree
• Island sink drain shall serve no other fixtures.
• Cleanout shall be installed in the vertical portion of foot vent.

Combination Waste and Vent System

• Shall only be permitted where structural conditions preclude the installation of conventional systems.
• Any branch exceeding 4.5m in length shall be separately vented.
• The only vertical pipe of a combination waste and vent system shall be the connection between the fixture drain and the horizontal combination waste and vent pipe. The vertical distance shall not exceed 8 feet (2438 mm).
• Vent connection shall be downstream of the uppermost fixtures.
• Min. diameter of traps shall be 2 pipe sizes larger than any fixture, tailpiece or connection.
• Tailpiece shall not exceed 0.6m
• No water closet or urinal shall be installed.
• 1, 2 or 3 unit fixtures remotely located from the sanitary system and adjacent to a combination waste and vent system are permitted to be connected in conventional manner.
• A floor drain normally requires a 2" trap and waste. On combination waste and vent system both trap and waste must be increased 2 pipe size, which will make the trap 3".
• The tailpiece between the floor drain and its trap should be 2" normal size to ensure that the amount of wastewater entering the trap only partially fills the waste branch.
• A 3" floor drain require 4" trap
• A 4" floor drain require 5" trap
• Pipe size recognized for this purpose are 2", 2.5", 3", 3.5", 4", 4.5", 5", 6".

Air Admittance Valves (AAV)

• The air-admittance valve (AAV) is a device designed to allow air to enter the drainage system to balance the pressure and prevent siphonage of the water trap when negative pressure develops in the system.
• Used on individual vents, branch vents, and circuit vents instead of terminating vents to the exterior of the structure.

Circuit Venting

• Maximum of eight fixtures connected to a horizontal branch drain
• Circuit vent connection shall be located between the two most upstream fixture drains and shall not receive discharge of any soil or waste.
• Maximum slope of the vent section of the horizontal drain shall be 8%.
• Relief vent shall be provided for circuit vented horizontal branches receiving the discharge of four or more water closets and connecting to a drainage stack that receives the discharge of soil or waste from upper horizontal branches.
• Relief vent shall connect to the horizontal branch drain between the stack and the most downstream fixture drain of the circuit vent.
• Additional fixtures are permitted to discharge to the horizontal branch drain, such fixtures shall be located on same floor as circuit-vented fixtures and shall be either individually or common vented.

Waste Stack Vent

• A waste stack shall be considered a vent for all fixtures discharging to the stack when installed according to requirements.
• Waste stack shall be vertical, and horizontal/vertical offsets are prohibited.
• Every fixture drain shall connect separately to the waste stack.
• Shall not receive discharge from water closet or urinals.
• Stack vent shall be provided for the waste stack with equal size of waste stack.
• Offsets shall be permitted for stack vent and shall be located at least 6" above the flood level of the highest fixture.
• The size of waste stack shall be based on total discharge to the stack and shall be the same size throughout its length.