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Under the IPC as adopted by Idaho, what is the minimum size of a building sewer?

2 inches

3 inches

4 inches

6 inches

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Free Journeyman Plumber Practice Test by State 2026: 4,700+ Questions24 min read

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Key Facts: ID Plumber Exam

70%

Passing Score

Idaho Division of Occupational and Professional Licenses (DOPL)

100

Questions

3 hours limit

~$195

Exam Fee

PSI (IAPMO exam)

IPC

Code Base

Idaho adoption

Idaho's journeyman plumber exam is based on the IPC (Idaho State Plumbing Code) and administered by PSI (IAPMO exam). Idaho uses the IAPMO-developed exam. The Idaho State Plumbing Code is based on the IPC with state-specific amendments for cold climate and rural water systems. The exam requires 70% to pass and tests drainage, water supply, venting, gas piping, and fixture knowledge.

Sample ID Plumber Practice Questions

Try these sample questions to test your ID Plumber exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1Under the IPC as adopted by Idaho, what is the minimum size of a building sewer?

A.2 inches

B.3 inches

C.4 inches

D.6 inches

Explanation: Per IPC building sewer requirements, the minimum size is 3 inches under the IPC. This ensures adequate capacity for the building drainage load and allows for proper maintenance access.

2Per the IPC as adopted by Idaho, what is the minimum slope for a 4-inch horizontal drainage pipe?

A.1/16 inch per foot

B.1/8 inch per foot

C.1/4 inch per foot

D.1/2 inch per foot

Explanation: Per IPC drainage slope tables, horizontal drainage pipes 3 inches and larger require a minimum slope of 1/8 inch per foot. This ensures adequate velocity (approximately 2 fps) to transport solids through the drainage system.

3What is the DFU value for a residential water closet (1.6 gpf) under the IPC?

A.2 DFU

B.3 DFU

C.4 DFU

D.6 DFU

Explanation: Per IPC fixture unit tables, a residential water closet with 1.6 gpf is rated at 3 DFU. This value is used for drainage and vent pipe sizing calculations throughout the plumbing system.

4Per the IPC as adopted by Idaho, what is the maximum distance between cleanouts on a horizontal drainage pipe?

A.50 feet

B.75 feet

C.100 feet

D.150 feet

Explanation: Per IPC cleanout requirements, cleanouts must be installed at intervals not exceeding 100 feet on horizontal drainage lines. Proper cleanout spacing ensures the entire system can be maintained and cleared of blockages.

5Under Idaho regulations, what type of backflow preventer is required for a high-hazard cross-connection?

A.Atmospheric vacuum breaker (AVB)

B.Pressure vacuum breaker (PVB)

C.Double check valve assembly (DCVA)

D.Reduced pressure zone (RPZ) assembly

Explanation: Per IPC backflow prevention requirements, a reduced pressure zone (RPZ) assembly is required for high-hazard cross-connections. The RPZ provides the highest level of protection with a relief valve between two check valves.

6Per the IPC as adopted by Idaho, what is the minimum water supply pipe size for a bathtub with shower?

A.3/8 inch

B.1/2 inch

C.3/4 inch

D.1 inch

Explanation: Per IPC fixture supply sizing tables, the minimum supply pipe size for a bathtub with shower is 1/2 inch. This ensures adequate flow and pressure at the fixture for proper operation.

7What is the maximum water temperature setting for a residential water heater per the IPC?

A.110°F

B.120°F

C.140°F

D.180°F

Explanation: Per IPC hot water requirements, the maximum delivery temperature at residential fixtures is 120°F. Anti-scald devices or thermostatic mixing valves must limit output temperature to prevent burns.

8Per the IPC as adopted by Idaho, what is the minimum trap seal depth for a standard plumbing fixture?

A.1 inch

B.2 inches

C.3 inches

D.4 inches

Explanation: Per IPC trap requirements, the minimum trap seal depth is 2 inches and the maximum is 4 inches. The water seal prevents sewer gases from entering the building through fixture drains.

9Under the IPC as adopted by Idaho, what is the minimum vent pipe size?

A.3/4 inch

B.1 inch

C.1-1/4 inches

D.1-1/2 inches

Explanation: Per IPC venting requirements, the minimum vent pipe size is 1-1/4 inches. No vent pipe shall be less than 1-1/4 inches in diameter. The vent must also be at least one-half the diameter of the drain it serves.

10Per the IPC as adopted by Idaho, what is the maximum static water pressure in a building distribution system?

A.60 psi

B.80 psi

C.100 psi

D.125 psi

Explanation: Per IPC water pressure requirements, water pressure shall not exceed 80 psi static. Where pressures exceed 80 psi, a pressure-reducing valve must be installed to prevent fixture damage and pipe noise.

About the ID Plumber Exam

Idaho journeyman plumber exam uses the IAPMO exam administered by PSI under DOPL. Based on the Idaho State Plumbing Code (IPC with amendments). Tests drainage, water supply, venting, gas piping, and Idaho-specific code provisions.

Questions

100 scored questions

Time Limit

3 hours

Passing Score

70%

Exam Fee

~$195 (Idaho Division of Occupational and Professional Licenses (DOPL))

ID Plumber Exam Content Outline

25%

Drainage & Waste Systems

Drain sizing, DFU calculations, slope requirements, cleanouts per IPC

20%

Water Supply & Distribution

Pipe sizing, backflow prevention, water heaters, pressure regulation per IPC

20%

Venting Systems

Vent sizing, wet venting, AAVs, vent termination, circuit venting per IPC

15%

Gas Piping

Gas pipe sizing, appliance venting, pressure testing, BTU calculations per IFGC

20%

Fixtures, Materials & Idaho Code

Fixture installation, materials, joints, permits, inspections, and Idaho-specific requirements

How to Pass the ID Plumber Exam

What You Need to Know

Passing score: 70%
Exam length: 100 questions
Time limit: 3 hours
Exam fee: ~$195

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

ID Plumber Study Tips from Top Performers

1Master IPC drainage fixture unit (DFU) values and pipe sizing tables

2Study backflow prevention device selection and cross-connection control

3Memorize minimum pipe sizes, slopes, and clearances for common fixtures

4Practice gas pipe sizing calculations using IFGC tables

5Understand wet venting and circuit venting provisions in the IPC

6Learn Idaho-specific permit and inspection requirements

Frequently Asked Questions

What code does Idaho use for the plumber exam?

Idaho uses the IPC (Idaho State Plumbing Code). The exam covers drainage, venting, water supply, gas piping, and fixture requirements as adopted by the state.

Who administers the Idaho plumber exam?

The exam is administered by PSI (IAPMO exam) under the Idaho Division of Occupational and Professional Licenses (DOPL).

How many questions are on the Idaho plumber exam?

The Idaho plumber exam has approximately 100 questions with a 3 hours time limit. A score of 70% is required to pass.

Is the ID plumber exam open book?

Most PSI (IAPMO exam)-administered plumber exams allow a bound copy of the adopted code. Check with the Idaho Division of Occupational and Professional Licenses (DOPL) for approved reference materials.