Plumbing Venting

Concept

Vents next to traps are allowed only a limited length. You must reach a dry stack to be 'home free'. The dry stack can be any length - it is effectively as if the appliance is connected to the outside. The purpose of traps is to trap odor, the purpose of vents is to prevent water from being siphoned out of the trap.

Design

• 2" trap must be 8' from vent, 1.5" must be 6' from vent. [1]
• Circuit venting classifies 4" drain pipe as a horizontal vent, under the assumption that circuit is never more than at full capacity of 4" pipe. See p. 14 at [2]
• AAV inlet must be at least 4" above the horizontal it serves. [3]. But, still need one vent to outside even if you have AAVs.
• Vent to drain distances included. Island venting. Air admittance valves. Engineered vent with sump pump and air admittance - like under sink macerator pump. [4]
• Drainage fixture unit - DFU - 7.5gpm or cubic foot of water through 1.25" pipe. Table for appliances and DFUs - [5]. DFUs based on pipe size - 2" is 6 DFUs - [6]
• Vents are 10' away from windows or air intakes, or 3 feet above. [7] Must be >10' above ground. [8]
• Good openslides on basics - [9]
• Vent stack vs stack vent - a stack vent is required in addition to vent stack for 5 stories or more [10]
• Island venting - for example an island sink as in this video - [11] - you can use an air admittance valve, or you can use an island fixture vent loop.
• Vent exends 6" above roof, except if roof is used for purposes other than weather protection - in which case it's 7'. [12]
• Vent is half diameter of drain served. [13]
• Washing machine needs a trap - [14]
• Vent stacks can run up the side of a house - [15]
• Total vent cross sectional area must equal total drain cross sectional area. See point 6 at [16]. Note that air admittance valves add to the total cross sectional vent area.
• 1/8" slope per foot is acceptable for 3" pipe - [17]

Internal Links

• Common Exhaust Chimney (A Concept Wherein All the Vent Pipes are Connected to a Central Outlet (Essentially like how there is one Black Water out, not 50 different pipes out

External Links

• The Wikipedia Page on Plumbing Venting