Idaho Plumbing Contractor Exam

Idaho Plumbing Contractor Exam: Complete 2026 Study Guide

Passing the Idaho plumbing contractor exam is the gateway to running your own plumbing business — legally pulling permits, supervising crews, and taking on residential, commercial, and industrial projects across the state. That's a serious credential, and the exam reflects it. With 100 questions covering everything from the 2017 Idaho State Plumbing Code to federal labor law, you need a solid plan going in. This guide breaks down exactly what to expect, what to study, and how to prepare efficiently so you walk out of the test center with a passing score.

Idaho Plumbing Contractor Exam Overview

The Idaho plumbing contractor license test is administered by PSI and consists of 100 scored questions answered in 240 minutes (4 hours). You need to answer 75 of those 100 questions correctly — a 75% passing score. Your result appears on screen the moment you finish, so there's no waiting by the mailbox.

The exam is open book, which is a genuine advantage — but it rewards candidates who know their references well, not those who plan to look up every answer. You're allowed to bring the Division of Occupational & Professional Licenses Contractor's Business and Law Reference Manual and either the 2015 Uniform Plumbing Code or the 2017 Idaho State Plumbing Code. Time is real pressure here — 240 minutes sounds generous until you're working through calculation problems.

All exams are taken at a PSI test center. Check the official exam bulletin for current scheduling, location, and ID requirements.

What Topics Does the Idaho Plumbing Contractor Exam Cover?

The exam draws from two main sources: the 2017 Idaho State Plumbing Code and the Contractor's Business and Law Reference Manual. Here's how the weight breaks down by topic, from heaviest to lightest:

Contractor's Business and Law Reference Manual — Section 6 (20 questions)
Federal employment law: anti-discrimination statutes (Title VII, ADA, ADEA, GINA, EPA), wage and hour rules under the FLSA, FMLA leave entitlements, and federal contractor labor requirements like Davis-Bacon.

Contractor's Business and Law Reference Manual — Section 7 (15 questions)
Contractor insurance types (CGL, builder's risk, professional liability, EPLI), workers' compensation obligations in Idaho, surety bonds, unemployment insurance, and independent contractor classification.

Contractor's Business and Law Reference Manual — Section 11 (10 questions)
OSHA: employer responsibilities, the general duty clause, recordkeeping forms (300, 300-A, 301), inspection priorities, PPE requirements, and fall protection systems.

Plumbing Sizing Using Schematics (8 questions)
Calculation-heavy problems using actual schematic drawings provided during the exam. Expect to size water supply pipes, determine fixture unit totals, and size drainage and vent piping using code tables.

2017 Idaho State Plumbing Code — Chapters 5, 6, 8, and 9 (5 questions each)
Water heater installation and venting (Ch. 5); backflow prevention, pipe materials, and pressure regulation (Ch. 6); indirect waste systems and condensate disposal (Ch. 8); vent sizing, termination requirements, and wet venting (Ch. 9).

2017 Idaho State Plumbing Code — Chapter 12 (4 questions)
Gas piping materials, sizing methods, underground installation rules, pressure testing, and regulator requirements.

2017 Idaho State Plumbing Code — Chapters 7 and 10 (3 questions each)
Drainage fixture units and drainage pipe sizing (Ch. 7); trap requirements, prohibited trap types, and trap arm length limits (Ch. 10).

Contractor's Business and Law Reference Manual — Sections 8 and 13 (3 questions each)
Bidding, estimation, and specifications (Sec. 8); mechanic's lien rights, filing deadlines, and enforcement under Idaho Title 45 (Sec. 13).

2017 Idaho State Plumbing Code — Chapters 11 and 2 (2 and 1 questions)
Storm drainage sizing and subsoil drains (Ch. 11); plumbing terminology (Ch. 2).

Contractor's Business and Law Reference Manual — Sections 1–5, 9, 10, and 12 (1–2 questions each)
Business planning, accounting, business entities, DOPL licensing, contracts, project management, and tax obligations.

Sample Questions From the Idaho Plumbing Contractor License Test

These questions represent the depth and style you'll face on exam day. Give them a real try — then start a free practice exam to see how you score across all topic areas.

Question 1 — Plumbing Sizing (Hard)
You are sizing the water supply for a small office building with flush tank water closets as the highest fixtures. The minimum daily service pressure is 50 psi, the highest fixture is 30 feet above the water main, and the developed length of pipe is 150 feet. What is the pressure available for friction loss (assuming no water meter)?

• A) 29.10 psi
• B) 21.10 psi
• C) 35.10 psi
• D) 27.10 psi

Question 2 — OSHA Inspection Priorities (Hard)
In the OSHA worksite inspection priority ranking, which category falls immediately below fatalities and hospitalizations?

• A) Imminent danger situations
• B) Targeted inspections for particular hazards
• C) Worker complaints and referrals
• D) Follow-up inspections

Question 3 — Water Supply Fixture Units (Medium)
A project schematic shows a commercial restroom with 10 public-use water closets (1.6 GPF flushometer valves) and 5 public-use lavatories. What is the total water supply fixture unit (WSFU) demand for these fixtures?

• A) 45 WSFU
• B) 50 WSFU
• C) 55 WSFU
• D) 60 WSFU

Question 4 — Fall Protection (Medium)
Which of the following items is specifically prohibited from use as a fall arrest component in a personal fall arrest system?

• A) Lanyards
• B) Horizontal lifelines
• C) Deceleration devices
• D) Body belts

Question 5 — FLSA Overtime Exemption (Hard)
Under the FLSA, commissioned sales employees of retail or service establishments are exempt from overtime if more than half of their earnings come from commissions and they average at least what amount per hour worked?

• A) The federal minimum wage
• B) Twice the minimum wage
• C) Two and one-half times the minimum wage
• D) One and one-half times the minimum wage

Not sure how you did? Our free exam gives you 10 questions instantly — no account required.

What Types of Questions to Expect

Our practice bank covers every exam topic with a total of 816 practice questions. Here's what each area looks like in practice:

• Chapter 2 — Terminology (24 questions): Definitions for drainage, venting, trap, water supply, and backflow terms.
• Chapter 5 — Water Heaters (34 questions): Permit requirements, location rules, TPR valves, combustion air, and venting selection.
• Chapter 6 — Water Supply (36 questions): Backflow prevention device selection, pipe materials, joining methods, and pressure regulation.
• Chapter 7 — Drainage (20 questions): DFU values, drainage pipe sizing, approved materials, joint methods, and cleanout placement.
• Chapter 8 — Indirect Waste (20 questions): Air gaps, standpipe sizing, food service requirements, and condensate disposal.
• Chapter 9 — Venting (20 questions): Vent pipe sizing, grade and rise requirements, termination rules, and wet venting configurations.
• Chapter 10 — Traps (12 questions): Trap requirements, prohibited types, seal depth, arm length limits, and floor drain protection.
• Chapter 11 — Storm Drainage (10 questions): Conductor materials, primary/secondary roof drain systems, and sizing by rainfall data.
• Chapter 12 — Gas Piping (33 questions): Pipe materials, sizing methods, underground installation, pressure regulators, and pressure testing.
• Plumbing Sizing — Schematics (210 questions): The largest category by far — WSFU calculations, water supply pipe and meter sizing, DFU values, drainage sizing, and vent sizing, all using table-based methods.
• Business Manual Section 1 (7 questions): Business plans, executive summaries, and operations planning.
• Business Manual Section 2 (7 questions): Selecting CPAs, attorneys, and insurance agents.
• Business Manual Section 3 (7 questions): Business entity types and Idaho registration requirements.
• Business Manual Section 4 (7 questions): DOPL oversight, licensing by trade, and penalties for unlicensed work.
• Business Manual Section 5 (7 questions): Financial statements, accounting methods, and financial ratios.
• Business Manual Section 6 (113 questions): Federal employment and labor law — the heaviest real-exam topic.
• Business Manual Section 7 (99 questions): Insurance, workers' comp, bonds, and contractor classification.
• Business Manual Section 8 (24 questions): Bidding types, estimation methods, and specification components.
• Business Manual Section 9 (13 questions): Contract elements, Idaho Statute of Frauds, retention rules, and contract types.
• Business Manual Section 10 (22 questions): Project management phases, CPM scheduling, and cost control.
• Business Manual Section 11 (70 questions): OSHA duties, recordkeeping, inspections, PPE, and fall protection.
• Business Manual Section 12 (7 questions): Tax filing by entity type, Idaho sales and use tax, and contractor tax classification.
• Business Manual Section 13 (14 questions): Lien rights, filing deadlines, priority, enforcement, and bond releases.

Required Study Materials

Because the Idaho DOPL plumbing contractor PSI exam is open book, your references are working tools — not just background reading. You need both approved books, and you need to know them well.

2017 Idaho State Plumbing Code — This is your primary technical reference. Forty-three of the 100 exam questions come from the plumbing code chapters, plus the 8 schematic sizing questions rely on its tables directly. Bookmark your fixture unit tables, drainage sizing tables, and vent sizing charts — you'll use them repeatedly.

Division of Occupational & Professional Licenses Contractor's Business and Law Reference Manual — This free PDF covers Sections 1–13 and accounts for roughly half the exam. It must be printed, hole-punched, and placed in a three-ring loose-leaf binder before test day. Pre-exam highlighting, underlining, and permanent indexing tabs are allowed. Post-its and temporary markers are not permitted inside the exam room, and you may not write in your materials during the exam session.

Both references are essential. Bring them both, know them well, and organize them so you can find answers quickly under time pressure.

Study Tips for the Idaho Plumbing Contractor Exam

Start early. Give yourself at least three to six weeks of focused preparation. Use the official exam bulletin as your roadmap — it lists exactly what's tested and at what weight.

Build finding-it-fast skills, not just memory. This is open book, so the real skill is locating the right table or code section quickly. Practice flipping to Table 610.4 for water supply sizing or Table 702.1 for drainage units without hesitation.

Prioritize by exam weight. Sections 6 and 7 of the Business Manual together account for 35 questions — more than a third of the exam. Federal labor law and contractor insurance deserve serious attention. Gas piping (Chapter 12) and the schematic sizing questions are also high-yield.

Set a high practice target. Aim for three consecutive practice attempts at 80% or higher before your exam date. Setting your bar above the 75% cut score gives you a real margin on test day.

Use timed practice. Untimed PDF review doesn't prepare you for managing 240 minutes across 100 questions. Our full practice exam matches the real exam's format, question count, and time limit — every attempt draws from a large question pool, so you're never seeing the same exam twice.

Start free, then go full. Our free practice exam gives you 10 questions right now — no account needed — to get a feel for the format. When you're ready for serious preparation, upgrade to the full practice exam for topic-by-topic score breakdowns that show exactly where to focus next.

Frequently Asked Questions

How much does the Idaho Plumbing Contractor Exam cost?
The examination fee is $75.00. Fees are not refundable or transferable, and they're valid for one year from the date of payment, so schedule your exam promptly after registering.

How many questions are on the exam, and how long do I have?
The exam has 100 questions with a 240-minute (4-hour) time limit.

What is the passing score?
You need 75 correct answers — 75% of 100. PSI displays your score on screen immediately when you finish. If you don't pass, you'll receive a diagnostic report showing your performance by topic.

How do I register?
Register online through the exam registration page, available 24 hours a day, or call PSI at 855-340-3713 during business hours.

Is the exam open book? What can I bring?
Yes, it's open book. You may bring the Contractor's Business and Law Reference Manual (printed, hole-punched, in a three-ring binder) and either the 2015 Uniform Plumbing Code or the 2017 Idaho State Plumbing Code. No other materials are permitted.

Are there rules about how I prepare my reference binder?
Yes. The Contractor's Business and Law Reference Manual must be printed, hole-punched, and placed in a three-ring loose-leaf binder. Pre-exam highlighting, underlining, and permanent index tabs are allowed. Post-its, temporary markers, and any writing during the exam session are strictly prohibited.

What ID do I need?
One current, unexpired, government-issued photo ID with your name, signature, and photograph — a driver's license, state ID, U.S. passport, military ID, or alien registration card all qualify. Temporary DMV paper IDs are accepted only when accompanied by the original expired ID.

What happens if I fail? Can I retake the exam?
Yes. You may retake the Idaho plumbing contractor exam as many times as needed. Each attempt requires a new $75.00 examination fee.

How do I cancel or reschedule?
You must cancel at least 2 days before your scheduled date to avoid forfeiting your fee. Call PSI at 855-340-3713 or cancel through the PSI website. Voicemail and email are not accepted forms of cancellation.

When will I get my results?
Immediately. Your score appears on screen the moment you complete the exam, and a printed score report is provided. If you did not pass, the report includes a topic-by-topic diagnostic breakdown.

Ready to Start Preparing?

The Idaho plumbing contractor license opens the door to managing the full scope of plumbing work — residential, commercial, and industrial — across the state. The exam is rigorous, but it's completely achievable with organized, consistent preparation. Gather your reference materials, build your look-up speed, and set your practice bar at 80% or higher before test day.

Start today with our free practice exam — 10 questions, no account required, instant results. When you're ready to go deeper, our full practice exam mirrors the real Idaho DOPL plumbing contractor PSI exam with 100 questions, a 4-hour timer, and detailed topic scoring. You've put in the hours in the field — now let's get you licensed.