EstatePass

Venting — Plumber Practice Questions

69 questions · 15% of the Plumber exam

Worked questions

1. A vent system exists so that air pressure swings inside the drainage piping stay small enough to leave fixture trap seals intact. Under the IPC, what is the largest pneumatic pressure differential a fixture trap seal may be subjected to?

  • 1 inch of water column
  • B1 pound per square inch

    One pound per square inch is roughly 27.7 inches of water column, which would empty a trap seal many times over. This is a unit-scale error, confusing water supply pressure units with the very small pneumatic pressures that matter in a drain.

  • C4 inches of water column

    Four inches of water column is the maximum depth of a trap seal, not the maximum pressure differential allowed across it. Allowing a differential equal to the full seal depth would guarantee seal loss rather than prevent it.

  • D10 inches of mercury

    Ten inches of mercury is a deep vacuum used in refrigeration evacuation work, roughly 136 inches of water column. Nothing in a gravity drainage system operates anywhere near that, and no trap seal would survive it.

Why A is correct

The code fixes the design target at 1 inch of water column of pneumatic differential at any trap seal. Vent sizing, trap arm limits and stack relief venting are all engineered to keep the system inside that band, because pressure larger than that will siphon or blow a standard 2-inch to 4-inch trap seal and let sewer gas into the building.

What this question is testing

Whether the candidate understands the design basis of the whole venting chapter rather than memorizing isolated numbers, and whether they can separate pneumatic pressures in a drain from the supply-side pressures measured in psi. It also checks unit fluency between inches of water column, psi and inches of mercury.

On the job

On a real callback for sewer odor, the pressure that pulled the seal was never large enough to feel or hear. A 3-inch stack serving five floors with an undersized vent can swing well past 1 inch of water column every time an upper-floor water closet flushes, and the ground-floor lavatory gurgles and then smells. Understanding that the target is 1 inch, not 1 psi, is what makes plumbers take vent sizing seriously instead of treating vents as optional pipe.

Memory technique

One inch of water column is all the pressure a trap seal can take.

Exam tip

If a venting answer is expressed in psi, it is almost certainly wrong; drainage pressures are expressed in inches of water column.

Where to look it up

Chapter 9, the opening general section on trap seal protection, states the pressure limit.

2. Taking a dry vent off the side or bottom of a horizontal drain would let drainage enter the vent. Under the IPC, at what point on a horizontal drain pipe must a dry vent connection be made?

  • Above the centerline of the horizontal drain pipe
  • BAt the invert of the horizontal drain pipe

    The invert is the bottom inside surface of the pipe, where all the waste and solids travel. A vent taken from there fills with drainage on the first discharge and plugs solid soon after.

  • CAt the springline on either side, below the centerline

    The springline is the widest point of the pipe at mid-height, at or just below the centerline. A connection there is still in the flow path during a heavy discharge and does not satisfy the requirement.

  • DAt any point on the pipe as long as the vent rises immediately

    Requiring only that the vent rise immediately ignores where the connection itself is made. A vent that leaves the bottom of the drain and then turns up has already taken on waste at the fitting.

Why A is correct

Connecting above the centerline keeps the vent opening out of the flowing waste. A horizontal drain sized and sloped correctly runs part full, so the upper portion of the pipe carries air. Tapping into that air space gives the vent a clear path and keeps solids and grease out of a pipe that has no water to scour it.

What this question is testing

Understanding of how a partially full horizontal drain actually flows and why the air space above the flow is where a vent belongs. It also checks fitting orientation knowledge, which the exam probes indirectly through connection-point questions.

On the job

This is one of the most common rough-in corrections on residential work, usually because a crawl space or joist bay forces someone to roll a fitting to make it fit. The tell is a sanitary tee installed on its side or upside down. Once a vent has been fed waste it never recovers, and the callback is a slow drain years later that nobody connects to the fitting orientation.

Memory technique

Waste rides the bottom, air rides the top, so vents come off the top.

Exam tip

If a venting answer involves the bottom or side of a horizontal drain, it is wrong. Vents come off the top.

Where to look it up

Chapter 9, the vent connections and grades section.

3. A vent terminal discharges sewer gas, so the code keeps it away from anything that draws air into a building. Under the IPC, what separation must be maintained between an open vent terminal and a door, openable window or air intake?

  • AAt least 4 feet horizontally, or at least 2 feet above the top of the opening

    Four feet horizontally is far too little separation, and 2 feet of height was the figure in earlier editions rather than the current one. This is the answer that catches plumbers working from an older memory of the section.

  • BAt least 25 feet horizontally, with no height alternative permitted

    Twenty-five feet with no height alternative overstates the horizontal distance and removes a compliance path the code actually provides. On a tight roof the height option is often the only workable one.

  • CAt least 10 feet horizontally, or at least 1 foot above the top of the opening

    One foot above the opening is not enough vertical separation to substitute for horizontal distance. The horizontal figure in this choice is right, which makes the wrong height easy to overlook.

  • At least 10 feet horizontally, or at least 3 feet above the top of the opening

Why D is correct

The rule offers two compliance paths, and either one satisfies it: keep the terminal 10 feet away horizontally, or carry it 3 feet above the top of the opening. Sewer gas leaving a terminal is warmer and lighter than outside air and tends to rise, which is why extra height works as a substitute for horizontal separation.

What this question is testing

Whether the candidate reads a rule that offers alternative compliance paths as alternatives rather than as a single combined requirement, and whether they are current on the vertical dimension, which has changed across editions.

On the job

Rooftop equipment has multiplied, and a vent stack that was clear when the building was built often ends up next to a new outside air intake or a rooftop unit added during a tenant fit-out. When that happens the fix is to extend the vent upward rather than relocate it, because 3 feet of pipe is cheaper than re-routing a stack. Knowing both compliance paths lets you offer the cheap fix immediately.

Memory technique

Ten feet away or three feet over the top.

Exam tip

Rules written with the word or give you a choice. Pick the path that is cheaper on the job in front of you.

Where to look it up

Chapter 9, the location of vent terminal subsection. UPC differs on this point — follow the code your state has adopted.

4. A homeowner wants a satellite antenna mast fastened to the vent pipe that projects above the roof, since it is already there and standing straight. What does the IPC say about using a vent terminal that way?

  • AIt is acceptable once the mast has been bonded to the building grounding electrode system, which is the only condition the code places on that use.

    Bonding answers an electrical hazard and is a separate matter. It does nothing about the wind load a mast puts into a plastic or cast iron vent and into the roof penetration below it.

  • A vent terminal may not be used to support a flagpole, antenna or similar item unless the piping has been anchored in an approved manner
  • CIt is acceptable on any vent 3 inches or larger, because pipe of that diameter is stiff enough to carry the wind load of a small mast.

    Diameter is not the issue. A 3-inch vent is still supported only for its own weight, and a taller pipe simply gives the wind more leverage on the joints below the roof line.

  • DIt is acceptable where the antenna is mounted within 12 inches of the roof surface, so the leverage on the piping stays minimal.

    Mounting low reduces leverage but does not make a vent a structural member, and the prohibition carries no height exception. The flashing still takes whatever load the mast delivers.

Why B is correct

The code specifically bars using a vent terminal to support a flagpole, antenna or similar item unless the piping is anchored in an approved way. The terminal is drainage piping designed for gravity flow, and wind load transferred through it damages joints and roof flashings.

What this question is testing

Whether the candidate knows the prohibited uses of a vent terminal in addition to its height and clearance requirements, and whether they recognize that an unrelated safety measure does not cure a mechanical prohibition. It also checks whether they can reason about a load path, since the failure here shows up as a roof leak rather than as a plumbing defect.

On the job

Every service plumber has found a satellite dish, a clothesline or a string of holiday lights tied to a vent stack, and the call usually comes in as a roof leak rather than a plumbing complaint. The pipe rocks in the wind, the flashing boot tears, and water runs down the outside of the pipe into the attic. Cutting the mast loose and installing a proper roof mount is cheaper than the drywall repair that follows a season of leaking.

Memory technique

A vent is a pipe for air, not a post for hardware.

Exam tip

The vent terminal section covers more than height; it also covers what may not be hung on the pipe.

Where to look it up

Chapter 9, the vent terminals section, including the subsection on prohibited use of the terminal. UPC differs on some terminal requirements, so follow the code your state has adopted.

5. During a remodel you find that a bathroom group's vent rises into the attic, turns, and simply ends in the open attic space several feet from the roof sheathing. What does the plumbing code require of that vent?

  • AIt is acceptable in a ventilated attic, because attic ventilation carries the sewer gas out through the soffit and ridge vents

    Attic ventilation moves air slowly and inconsistently, and the sewer gas has already entered the building by the time it reaches the soffit. Nothing in the code recognizes an attic as outdoor air.

  • BIt is acceptable if the open end is fitted with a screen and located at least 6 inches above the attic insulation

    A screen keeps animals out of an opening that should not exist. Height above insulation is an air admittance valve rule and has nothing to do with an open vent terminal.

  • CIt must be fitted with an air admittance valve at the point where it now ends inside the attic space

    An air admittance valve is a one-way device that admits air only. It may be permitted in some locations, but it is not the fix for a vent that was supposed to reach outdoor air, and installing one does not vent positive pressure out of the system.

  • It must be extended through the roof or through a sidewall so that it terminates in the outdoor air

Why D is correct

Terminating outdoors is what separates a vent from a hole in the drainage system. Extending it through the roof or through a sidewall at the required clearances puts the sewer gas outside the building envelope, which is the entire purpose of the terminal.

What this question is testing

Whether the candidate understands both functions of a vent terminal and knows that an interior space, however ventilated, is not an acceptable termination point.

On the job

Vents left short in attics are common in additions and in do-it-yourself work, and the symptom the homeowner reports is an odor in the upstairs hallway on windy days or a stain on the attic side of the sheathing from condensed moisture. It is a cheap fix while the attic is accessible and an expensive one after insulation is blown in. Whenever you are in an attic for any reason, follow the vents to the roof jack.

Memory technique

An attic is inside. Vents end outside.

Exam tip

A vent has to end outdoors. Any option that lets it end inside the building envelope is wrong regardless of what is added to it.

Where to look it up

IPC Chapter 9, the vent terminal provisions covering roof extensions and terminals near openings. The UPC states its own terminal heights and clearances, so verify in your adopted code.

6. A remodel needs a path to the roof for a new vent, and the only clear vertical route is an unused masonry chimney flue that also carries the vent connector for a gas water heater. What does the plumbing code say about running the vent up that flue?

  • AIt is permitted where the flue is lined and the vent is carried to the top of the chimney in one continuous piece

    A liner does not make a flue an approved plumbing vent path. The prohibition is about mixing the systems, not about the condition of the masonry.

  • It is prohibited; a plumbing vent may not terminate in or be run through a chimney or a gas vent
  • CIt is permitted where the appliance served by the flue is decommissioned and its connector is capped

    Decommissioning the appliance does not convert a chimney into plumbing vent piping. If a plumbing vent is to run in that chase, it runs as its own pipe, terminating on its own.

  • DIt is prohibited unless the vent is increased one pipe size for the portion inside the masonry chimney

    Pipe size has nothing to do with the prohibition. A larger pipe in a chimney is still a plumbing vent in a chimney.

Why B is correct

The prohibition is absolute because the two systems have incompatible jobs. Keeping plumbing vents out of chimneys and gas vents protects the appliance venting from obstruction and keeps sewer gas out of a flue that discharges near the roof line.

What this question is testing

Whether the candidate knows the prohibition on terminating plumbing vents in chimneys and gas vents and recognizes that conditions attached to the practice do not make it acceptable.

On the job

Old houses tempt everyone with an abandoned flue running straight from the basement to the roof, and remodelers use them as chases constantly. Running a properly sized and supported plumbing vent pipe up through a masonry chase as its own continuous pipe, terminating above the roof, is a different matter from terminating into the flue itself, and it is worth being precise about which one the inspector is looking at. Any flue still serving a fuel-burning appliance is off limits entirely.

Memory technique

Smoke goes up its own pipe; sewer gas goes up its own pipe.

Exam tip

Combustion venting and plumbing venting never share a passage. Treat any option that combines them as wrong.

Where to look it up

IPC Chapter 9, vent terminals, together with the appliance venting requirements in the mechanical and fuel gas codes. The UPC carries the same prohibition in its venting chapter, so the principle survives a code change even though the terminal dimensions do not.

7. A lavatory in a remodel would have a trap arm 10 feet long, which is beyond the permitted distance for its size. The contractor proposes to install an air admittance valve instead of extending a dry vent. What does the code require?

  • AThe valve solves the problem, because a valve serves as the vent regardless of how far it sits from the trap

    This is the most common misconception about these valves. They relax where the vent has to go, not how far the trap may sit from it.

  • BThe valve is acceptable if it is installed within 12 inches of the fixture trap it protects

    No rule ties a valve to within a foot of the trap. Inventing a tighter limit is as wrong as ignoring the real one.

  • CThe valve is not permitted for a lavatory, because valves may vent only fixtures without water seals

    Air admittance valves are routinely used on lavatories, sinks and other trapped fixtures. The restriction on their use is about location and system pressure, not about the presence of a trap.

  • The valve must still be located within the maximum distance permitted between that trap and its vent

Why D is correct

The trap arm limit exists to stop the fixture's own discharge from siphoning its seal, and that mechanism does not care what is on the far end of the vent. Putting a valve at the vent connection changes how the vent breathes, not where it is allowed to be.

What this question is testing

Whether the candidate understands that an air admittance valve substitutes for the vent terminal rather than for the vent connection, and that trap arm distance limits still apply.

On the job

Valves get treated as a universal solvent on remodels, and this is the case where they are not. A ten foot trap arm siphons its own trap whether the vent ends in a valve or on the roof. The practical fixes are the same as always: move the vent connection closer, enlarge the trap arm to buy distance, or rearrange the fixture. Watch for existing work where somebody stuffed a valve under a vanity at the end of a long run and the customer reports odor after every use.

Memory technique

The valve is the roof, not the vent. The trap arm rule never goes away.

Exam tip

A valve changes where the vent ends, never where it starts. Trap arm distance always applies.

Where to look it up

IPC Chapter 9, the air admittance valve provisions read together with the fixture vent section and its trap-to-vent distance table. The UPC limits these valves far more tightly, so verify in your adopted code.

8. A vent is proposed to terminate through a sidewall at a point 4 feet below an openable bedroom window and 5 feet to the side of it. Take as given the code rule that a vent terminal must be at least 3 feet above any opening within 10 feet of it. Does the proposed location comply?

  • AYes, because the terminal is more than 3 feet away from the window measured in a straight line

    The 3 foot dimension in the rule is a vertical measurement above an opening, not a straight-line separation. Applying it as a radius misreads the requirement.

  • BYes, because the rule applies only to terminals located above an opening, not below one

    Nothing in the rule limits it to terminals above openings. A terminal below an opening is the case the vertical requirement exists to prevent.

  • No, because the terminal is within 10 feet of the opening and is below it rather than 3 feet above it
  • DNo, because a sidewall terminal may never be located on the same wall as an openable window

    Sidewall terminals on a wall with windows are routine. They simply have to satisfy the distance or the height relationship to each opening.

Why C is correct

Sewer gas is warm and rises, so a terminal below an opening is the worst case rather than a neutral one. Inside the 10 foot radius the only compliant arrangement puts the terminal well above the opening, and this one is 4 feet under it.

What this question is testing

Whether the candidate can apply a two-part clearance rule to a specific geometry and recognize that a terminal below an opening does not satisfy an above-the-opening requirement.

On the job

Sidewall vent terminals get located by whatever is convenient on the elevation, and second-floor windows above them are easy to overlook from the ground. Walk the exterior with the elevations in hand and look up. This same relationship applies to doors, air intakes, and the soffit vents on a roof overhang, all of which count as openings drawing air into the building.

Memory technique

Ten feet away or three feet above. Underneath is always wrong.

Exam tip

Read clearance rules as either-or. Far enough away horizontally, or high enough above. Below never counts.

Where to look it up

IPC Chapter 9, the vent terminal provisions covering location relative to openings, read with the sidewall terminal requirements. The UPC uses its own dimensions for the same relationship, so verify in your adopted code.

61 more in the bank

Answers and explanations for these are in the app.

  • 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?

Practice all 69 Venting questions

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