Journeyman Plumber Practice Questions
These questions are written for anyone preparing for a journeyman plumber licensing exam. State and local exams are based on either the International Plumbing Code or the Uniform Plumbing Code, so the questions here stick to principles and values the two codes share, and the explanations point out the places where the IPC and UPC differ.
The pool covers drain, waste and vent principles, fixture units, water supply pressure and water hammer, backflow prevention devices, water heater safety, piping materials and the pipe math that shows up on every exam. Take the 10-question timed quiz as often as you like; every answer comes with the reasoning behind it.
Question of the day
Water supply · October 8
A washing machine's solenoid valve makes the supply pipes bang each time it snaps shut. What should the plumber install?
Quick-closing valves stop moving water suddenly, which creates a pressure shock, and both the IPC and the UPC require a water hammer arrestor where quick-closing valves are used. An expansion tank absorbs thermal expansion from the water heater, not the surge from a closing valve.
Show the answer
A. A water hammer arrestor near the quick-closing valve — Quick-closing valves stop moving water suddenly, which creates a pressure shock, and both the IPC and the UPC require a water hammer arrestor where quick-closing valves are used. An expansion tank absorbs thermal expansion from the water heater, not the surge from a closing valve.
10-question sample
Ten of the 15 sample questions, at random, one at a time, with the explanation after each answer. About five minutes. Full-length timed mock exams are in Pipeforge: Plumbing Tools.
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How to study for the Plumbing (journeyman) exam
- Find out which code your state adopts (IPC or UPC) and which edition, then study from that book, because fixture-unit tables, trap arm lengths and sizing tables differ between the two.
- Learn the DWV principles before the tables: why traps need vents, why trap arm length is limited and why slope matters, since exam questions test the reasoning as often as the numbers.
- Memorize the backflow device hierarchy (air gap, RPZ, double check, PVB, AVB) with the hazard level and the installation limits of each.
- Keep the pipe-math constants in your head: 0.433 psi per foot of water, 2.31 feet of water per psi and 1.414 for the travel of a 45° offset.
- On every water heater question, check the T&P relief valve details: setting, full-size discharge pipe, approved material, gravity drainage and no valves or threads at the end.
All 15 questions with answers
Open a question to see the answer and the reasoning. Topics: DWV and venting, Water supply, Backflow prevention, Water heaters, Materials and pipe math.
1. What liquid seal depth must a standard fixture trap have?
- 1 to 2 inches
- 2 to 4 inches
- 3 to 5 inches
- 4 to 6 inches
Answer: B. Both the IPC and the UPC (Chapter 10 in each) require a fixture trap to hold a liquid seal of not less than 2 inches and not more than 4 inches. Deeper seals are allowed only for special-purpose traps such as interceptors; a seal under 2 inches is lost too easily to evaporation and pressure swings.
Topic: DWV and venting
2. What is the main purpose of the vent piping in a drainage system?
- Carry sewer gas into the building drain
- Provide combustion air for gas appliances
- Keep air pressure equal on both sides of each trap seal
- Increase the velocity of flow in the drain
Answer: C. Vents admit and relieve air so that the pressure changes created by discharging fixtures cannot siphon or blow out a trap seal. They also let drains flow at normal velocity, but vents carry air only, never waste, and they have nothing to do with appliance combustion air.
Topic: DWV and venting
3. What is the minimum slope for a 2-inch horizontal drainage pipe?
- ⅛ inch per foot
- ¼ inch per foot
- ½ inch per foot
- 1 inch per foot
Answer: B. Both codes require ¼ inch per foot for a 2-inch horizontal drain (IPC Table 704.1 for 2½ inches and smaller; UPC Chapter 7 for all sizes). The codes differ on larger pipe: the IPC allows ⅛ inch per foot for 3- to 6-inch pipe, while the UPC allows ⅛ inch per foot only for 4-inch and larger with approval.
Topic: DWV and venting
4. Which fixture carries the largest drainage fixture unit (DFU) value in the code tables?
- Lavatory
- Kitchen sink
- Bathtub
- Water closet
Answer: D. A water closet is rated 3 to 6 DFU depending on flush volume, private or public use and which code applies, while a lavatory is 1 and a bathtub or domestic kitchen sink is typically 2. A DFU is a probability-based load value used to size drains and vents, not a flow rate in gallons per minute.
Topic: DWV and venting
5. The static pressure at a building's water service measures 95 psi. What does the code require?
- A pressure-reducing valve limiting static pressure to 80 psi or less
- Nothing; 95 psi is within the allowable range
- A booster pump to stabilize the flow
- A larger service pipe to reduce velocity
Answer: A. Both the IPC (Section 604) and the UPC (Section 608) require an approved pressure-reducing valve where static pressure exceeds 80 psi, set to hold the building distribution piping at 80 psi or less. Fire sprinkler and hose supplies are the usual exception, and a strainer upstream of the valve is standard practice.
Topic: Water supply
6. A washing machine's solenoid valve makes the supply pipes bang each time it snaps shut. What should the plumber install?
- A water hammer arrestor near the quick-closing valve
- A thermal expansion tank at the water heater
- A backflow preventer on the laundry supply
- A larger-diameter supply pipe only
Answer: A. Quick-closing valves stop moving water suddenly, which creates a pressure shock, and both the IPC and the UPC require a water hammer arrestor where quick-closing valves are used. An expansion tank absorbs thermal expansion from the water heater, not the surge from a closing valve.
Topic: Water supply
7. A shower head is 23 feet above the water meter. Ignoring friction, how much pressure is lost to elevation alone?
- About 5 psi
- About 10 psi
- About 23 psi
- About 53 psi
Answer: B. Water exerts 0.433 psi per foot of height, so 23 feet × 0.433 = about 10 psi. The 53 psi answer multiplies by 2.31, which is the conversion run the wrong way (2.31 feet of water per psi).
Topic: Water supply
8. A chemical feed on a boiler make-up line is a high-hazard cross-connection under continuous pressure that may see backpressure. Which backflow preventer is appropriate?
- Atmospheric vacuum breaker
- Double check valve assembly
- Reduced pressure zone (RPZ) assembly
- Hose connection vacuum breaker
Answer: C. A reduced pressure zone assembly protects against both backpressure and back-siphonage on high-hazard (contamination) connections, and its relief port must be able to discharge to a drain. A double check valve assembly is limited to low-hazard (pollution) connections, and vacuum breakers protect only against back-siphonage.
Topic: Backflow prevention
9. Which device protects only against back-siphonage and must not be installed with shutoff valves downstream or under continuous pressure?
- Double check valve assembly
- Reduced pressure zone assembly
- Pressure vacuum breaker
- Atmospheric vacuum breaker
Answer: D. An atmospheric vacuum breaker relies on a float check that must drop open when pressure is removed, so it cannot be under continuous pressure or have valves downstream, and it must sit at least 6 inches above the highest downstream outlet. A pressure vacuum breaker has a spring-loaded check and air inlet, so it allows downstream valves and continuous pressure and sits 12 inches above the highest outlet.
Topic: Backflow prevention
10. Away from walls or obstructions, how large must an air gap be between a water supply outlet and the flood-level rim of the fixture it serves?
- Equal to the effective opening, minimum ½ inch
- Twice the effective opening, minimum 1 inch
- Three times the effective opening, minimum 2 inches
- Four inches in every case
Answer: B. Both codes size an air gap at twice the diameter of the effective opening and never less than 1 inch (IPC Section 608 and UPC Section 603 tables), so a ¾-inch spout needs 1½ inches. A nearby wall or obstruction raises the requirement to three times the effective opening.
Topic: Backflow prevention
11. A standard temperature and pressure relief valve on a residential storage water heater is set to open at what temperature?
- 120°F
- 140°F
- 180°F
- 210°F
Answer: D. T&P relief valves open at 210°F and at a pressure not exceeding the tank's working pressure, commonly 150 psi, to prevent a tank rupture if the thermostat fails. The 120°F and 140°F figures are delivery and storage temperatures, not relief settings.
Topic: Water heaters
12. Which statement about the discharge pipe from a water heater T&P relief valve is correct?
- It may be reduced one pipe size to fit the drain
- It must end in a threaded fitting for a cap
- It must contain no valves and must drain by gravity
- It may connect directly to the sanitary drain
Answer: C. Both codes require the discharge pipe to be the full size of the valve outlet, made of an approved material, free of valves, shutoffs and traps, drained by gravity, serving only one relief valve, and ending without threads at an approved location through an air gap, never directly into the drain. Termination height is one place the codes differ: the IPC allows no more than 6 inches above the floor or receptor, while the UPC calls for 6 to 24 inches above the ground.
Topic: Water heaters
13. Which copper tube type has the thickest wall?
- Type K
- Type L
- Type M
- Type DWV
Answer: A. Type K (green markings) has the thickest wall and is used for underground water service, followed by Type L (blue) for most water distribution, Type M (red) for lighter residential lines where the code allows it, and Type DWV (yellow), the thinnest, for drain, waste and vent only.
Topic: Materials and pipe math
14. Which plastic pipe is acceptable for both hot and cold water distribution inside a building?
- CPVC
- PVC Schedule 40
- ABS
- Polyethylene (PE)
Answer: A. CPVC is rated for hot and cold water distribution, as is PEX. PVC and polyethylene are not rated for hot water and are limited to cold-water uses such as water service, and ABS is a drain, waste and vent material, never a potable water pipe.
Topic: Materials and pipe math
15. A 45° offset must move a run of pipe 14 inches sideways. What is the travel, the center-to-center length of the diagonal piece?
- 9.9 inches
- 14 inches
- 19.8 inches
- 28 inches
Answer: C. For a 45° offset, travel = offset × 1.414, so 14 × 1.414 = 19.8 inches, and the run (the distance the offset advances along the line) also equals 14 inches because the two legs of a 45° triangle are equal. Dividing by 1.414 (9.9 inches) is the common slip.
Topic: Materials and pipe math
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Frequently asked questions
Is the journeyman plumber exam based on the IPC or the UPC?
It depends on where you are licensed. Broadly, most eastern and central states use the International Plumbing Code and much of the West uses the Uniform Plumbing Code, usually with state amendments. Your licensing board lists the adopted code and edition.
Is the exam open book?
Many state plumbing exams allow the adopted code book, sometimes with tabs but no loose notes, while others are closed book. Check the candidate bulletin, and practice looking up tables quickly either way.
How many questions are on the real exam?
Question counts, time limits and passing scores vary by state, and many states add a separate business-and-law section. Confirm the details in your state's candidate bulletin and practice at the same pace.
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These questions were written by TapForge Studios for practice and are not taken from any real exam. They follow the standards and editions named above; the exam you sit may use a different edition, and the certifying body's outline governs. Not a substitute for the code books.