Venting — Plumber Practice Questions

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• Drainage risers on a multistory job include both a vent stack and a stack vent, and the two terms are easy to reverse. Which description correctly identifies a stack vent?
• A drainage stack that serves enough floors must be paired with its own vent stack rather than relying on the stack vent alone. Under the IPC, a vent stack is required once the drainage stack has at least how many branch intervals?
• The bottom of a vent stack has to be connected so that it can relieve the pressure surge that builds at the base of a drainage stack. Under the IPC, how is that base connection made?
• An individual vent may be arranged to protect more than one trap when the fixtures are placed correctly. Under the IPC, how many traps or trapped fixtures may a single individual vent serve when used as a common vent?
• A lavatory drain and a kitchen sink drain are common vented where they connect to a vertical drain at different levels, with the lavatory entering above the sink. Take the lavatory at 1 drainage fixture unit and the sink at 2 drainage fixture units. The sizing table you are given lists one and one-half inch pipe for up to 1 dfu, two inch pipe for up to 4 dfu, and three inch pipe for up to 6 dfu. What is the minimum size of the vertical drain section acting as the common vent?
• Wet venting lets the drain from one fixture serve as the vent for another, but the code limits which fixtures may be grouped that way. Under the IPC, what may a single horizontal wet vent serve?
• A horizontal wet vent receives the discharge of a lavatory at 1 drainage fixture unit, a bathtub at 2 drainage fixture units and a water closet at 3 drainage fixture units, all flowing into the wet-vented section. The wet vent size table you are given lists one and one-half inch pipe for 1 dfu, two inch pipe for 4 dfu, two and one-half inch pipe for 6 dfu, and three inch pipe for 12 dfu. What is the minimum wet vent size?
• Circuit venting lets one vent protect a row of fixtures on a horizontal branch drain instead of venting each one. Under the IPC, what is the greatest number of fixtures a single circuit-vented horizontal branch may serve?
• A circuit-vented horizontal branch sometimes needs a relief vent in addition to the circuit vent itself. Under the IPC, a relief vent is required for a circuit-vented branch that connects to a stack receiving discharge from above once the branch serves how many water closets?
• The developed length between a trap weir and its vent is limited so that the trap arm cannot lose its seal to self-siphonage. Using the IPC table of maximum distance from a fixture trap to its vent, what is the greatest developed length permitted for a 2-inch trap arm run at one-quarter inch per foot?
• A 2-inch trap arm runs 8 feet of developed length from the trap weir to the vent fitting at a slope of one-quarter inch per foot. The code limits the total fall in a fixture drain to one pipe diameter. How much does this trap arm fall over that run?
• The elevation at which a dry vent ties into a fixture drain determines whether the vent can still function when the fixture discharges. Under the IPC, where must that vent connection be made relative to the trap it protects?
• A dry vent may only turn and run horizontally after it has risen high enough that a stopped-up fixture cannot flood it. Under the IPC, how high must a dry vent rise before it may offset horizontally?
• The height of a vent terminal above the roof determines whether snow, debris or foot traffic can close it off. Under the 2021 IPC, how far above the roof must an open vent pipe terminate where the terminal has no protective cover?
• A vent that terminates through a sidewall rather than through the roof has to satisfy clearances that a roof terminal never faces. Under the IPC, what does a sidewall vent terminal require with respect to the lot line?
• Vent piping that runs on the outside of a building in a cold climate can ice closed and take the drainage system with it. Under the IPC, what is required for exterior vent piping in that situation?
• A very tall drainage stack develops pressure extremes that a vent stack alone cannot relieve, so the two risers are cross-connected at intervals. Under the IPC, where must relief vents be installed on a stack in a building having more than ten branch intervals?
• An individual vent is sized from the drain it protects rather than from the fixture itself. The IPC requires an individual vent to be at least one-half the diameter of the drain served and never smaller than 1-1/4 inches. The drain served is 3 inches and the vent has a developed length of 20 feet. What is the minimum vent size?
• Long vent runs lose capacity to friction, so the code adjusts the size once the run gets long enough. An individual vent serves a fixture on a 4-inch drain and has a developed length of 55 feet from the vent connection at the drain to the point where it ties into the vent stack. The vent must be at least one-half the diameter of the drain served, and a vent whose developed length exceeds 40 feet must be increased one nominal pipe size for its entire length. What size vent is required?
• A combination waste and vent system uses oversized horizontal drainage to carry air, but the code restricts what may discharge into it. Under the IPC, which of these discharges may such a system receive?
• Unlike ordinary drainage, a combination waste and vent pipe has a maximum slope rather than only a minimum, because too much fall drains the pipe and breaks the air path. A combination waste and vent pipe runs 24 feet horizontally and the code limits its slope to one-half unit vertical in 12 units horizontal. What is the greatest total fall permitted over that run?
• An air admittance valve has to sit high enough above the drainage piping that waste can never reach it and that it stays accessible. Under the IPC, how far above the horizontal branch drain or fixture drain being vented must an individual or branch type air admittance valve be located?
• A horizontal fixture branch was required by the drainage sizing tables to be 3 inches, but the crew actually installed it in 4-inch pipe. A vent must be not less than one-half the diameter of the drain served and never smaller than 1-1/4 inches, and this vent is short enough that no length increase applies. What is the minimum size of the vent serving that branch?
• A vent stack is being sized from the table that relates the size of the drainage stack, the fixture unit load carried by that stack, and a developed length. Which measurement does the code use as the developed length of the vent stack?
• Two vent stacks and one stack vent are carried up into an attic and joined into a single header that penetrates the roof at one point. How does the code require that header to be sized?
• A yoke vent is being installed between a 4-inch soil stack and the 3-inch vent stack that serves it. Take as given the code rule that a yoke vent is sized not smaller than the smaller of the two stacks it connects. What is the minimum size of that yoke vent?
• A yoke vent is being installed at a lower branch interval of a tall soil stack to relieve pressure in that part of the system. How must the two ends of that yoke vent be connected?
• A drainage stack has to jog sideways around a structural member. The offset is built so that the offsetting piece runs at 40 degrees from vertical, and fixtures connect to the stack both above and below the jog. What venting does that offset itself require?
• A soil stack comes down through a building and, below the lowest branch interval, offsets horizontally about 12 feet before continuing on to the building drain. No fixture connects to that offsetting run. What does the code require for the offset?
• In a nine-story building, the lavatory and the floor drain in the ground-floor restroom bubble and push water onto the floor whenever several upper-floor water closets discharge at once. Fixtures on the upper floors behave normally, and a camera shows the building drain clear. What is happening, and what corrects it?
• A house drains slowly at every fixture, traps gurgle in more than one room, and there is an odor in two bathrooms. Nothing inside the house was changed, and a drain machine run through the cleanout found the building drain and sewer clear. What is the most likely cause of symptoms appearing everywhere at once?
• An air admittance valve is being selected to vent a branch that serves a lavatory, a bathtub and a water closet in a remodeled bathroom. What determines the valve you are permitted to install?
• A metal finishing line discharges corrosive rinse water into a separate acid-resistant drainage system, and the designer proposes to save a roof penetration by venting that system with air admittance valves. What does the code permit here?
• A designer wants to wet vent the bathroom group on the second floor and the bathroom group directly below it on the first floor through a single common wet vent. What does the IPC wet venting method allow?
• A horizontal branch drain serving a row of circuit vented lavatories continues downstream past the circuit vent connection, and a janitor sink is now to be connected to that branch downstream of the circuit vent. How must the janitor sink be handled?
• You are laying out a stack in a dormitory that will be vented as a waste stack vent system. Setting aside the question of which fixtures may connect to it, what does the code require of the vertical piping itself?
• A waste stack vent system serves four floors, and each floor connects 9 drainage fixture units into the stack. Take these limits as given for this problem: a 3-inch stack in a waste stack vent system may carry a total of 48 drainage fixture units, with not more than 24 drainage fixture units connected within any single branch interval. Is a 3-inch stack acceptable?
• The single stack vent method lets fixtures be vented by the drainage stack they discharge into, with no separate vent stack. Compared with a conventionally vented stack carrying the same fixture unit load, what does the code require of that drainage stack?
• A kitchen sink in an island is vented by a loop that rises under the counter, returns downward and connects into the drainage system below the floor. What does the code require so that the loop can be maintained after the island is finished?
• You are roughing in the island vent loop for a kitchen sink with no wall behind it. How high must the vertical leg of that loop be carried before it turns over and heads back down?
• A basement slab is being poured with drainage roughed in and capped for a bathroom the owner will finish later. What does the code require with respect to venting at the time of that rough-in?
• The venting rules are written around the flood level rim of the fixture served. When the fixture is a floor drain set flush in a mechanical room slab, what is its flood level rim?
• A dry vent leaves a fixture group and runs 24 feet horizontally through a joist space before it reaches the vent stack. The vent has to be graded so that any condensate drains back toward the drainage piping, and you are pitching it at 1/8 inch per foot. How much higher is the vent where it meets the stack than where it left the fixture group?
• A vent is proposed to terminate through a sidewall about 6 feet horizontally from an openable window. Take as given the IPC rule that a vent terminal must be not less than 3 feet above, or not less than 10 feet horizontally from, any door, openable window or air intake. What must be done at this location?
• A 4-inch horizontal branch drain serving a battery of water closets is circuit vented, and the arrangement also requires a relief vent. Take as given the code rule that a relief vent is sized not less than one-half the diameter of the branch it serves, and that no vent may be smaller than 1-1/4 inches. What is the minimum relief vent size?
• A 2-inch vent has been carried up into an attic, and the crew proposes to reduce it to 1-1/2 inch for the last few feet so a smaller roof jack will fit. Under the 2021 IPC, what governs the size of the vent where it passes through the roof and terminates?
• A combination waste and vent system serves a line of floor sinks totaling 14 drainage fixture units. Take these capacities as given for this problem at the slope being used: a 2-inch combination waste and vent pipe carries 3 drainage fixture units, a 3-inch pipe carries 12, and a 4-inch pipe carries 20. What size horizontal pipe is required?
• A small commercial building's drainage system is being designed. Setting aside how individual fixtures are vented, what does the plumbing code require of the drainage system as a whole?
• A house is roughed in using air admittance valves at two fixture groups. When may those valves be installed relative to the required test of the drainage and vent system?
• A kitchen sink must be connected so that its trap arm runs 11 feet of developed length from the trap weir to the only vent location available. Take these maximum trap-to-vent distances as given data: 1-1/4 inch is limited to 5 feet, 1-1/2 inch to 6 feet, 2 inch to 8 feet, and 3 inch to 12 feet. What is the smallest trap arm size that places the vent within the permitted distance?
• The vent sizing rules in the plumbing code are written to hold conditions inside the drainage system within a stated limit. What is the vent system required to accomplish?
• You need two figures from the venting chapter: the maximum developed length permitted for a vent of a given size serving a stack, and the maximum distance a fixture trap may sit from its vent. How are those two figures organized in the code?
• An individual vent rises from a fixture drain in a wall. Under the IPC, where is the upper end of that vent permitted to go?
• A stack type air admittance valve is proposed to serve a drainage stack in a house rather than carrying that stack through the roof. Where must a stack type valve be located?
• A clothes washer standpipe rises well above the trap that serves it, and the trap connects through a horizontal run to its vent. When the maximum distance from the trap to the vent is checked, where does the measured length begin?
• An engineer proposes a vent layout for a high-rise that does not follow any of the prescriptive venting methods in the code. What does the plumbing code require before that system may be installed?
• An attic air handler's primary condensate drain has to reach a point of disposal, and the closest available pipe is the bathroom group's dry vent passing through the same attic. May the condensate line be connected into that vent?
• A drainage stack in a five-story building receives fixture connections on all five floors, so it has exactly five branch intervals. Take as given the code rule that a vent stack is required for a drainage stack having five branch intervals or more. What does the stack require?
• A trap arm is laid out with a straight run of pipe plus a 45-degree offset made with two fittings before it reaches the vent. When the trap-to-vent distance is checked against the table, how is that length determined?
• A combination waste and vent system serving a row of floor sinks was installed at a uniform slope of 5/8 inch per foot because the trench allowed it. Take as given the code limits for that system: not less than 1/8 inch per foot and not more than 1/2 inch per foot. What does the installed slope mean for that system?
• A horizontal branch drain serving a row of eight floor-mounted water closets is circuit vented. The owner now wants a ninth closet added to the same row and the same branch. Take as given the code limit of not more than eight fixtures on a circuit vented branch. What does the code require?

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