- The NV-C1 trade exam covers 23 domains across 120 scored questions, no single-topic shortcuts allowed.
- Drain, Waste, and Vents is the heaviest domain at 10 items; Gas Systems, Water Supply, Traps and Interceptors, and Isometric Analysis/Plumbing Mathematics each...
- Passing requires 84 of 120 correct (70%), within a five-hour, open-book, computer-administered session.
- Only five references are permitted in the testing room: UPC 2018, UMC 2018, NFPA 54 (2012), NFPA 58 (2014), and NFPA 13 (2019).
How the NV-C1 Blueprint Is Structured
The Nevada Plumbing and Heating Contractor (C-1) Trade Exam, administered by PSI Services LLC on behalf of the Nevada State Contractors Board, is not a generic plumbing quiz. It is the full C-1 trade examination - distinct from the plumbing-only C-1d exam - and it is built from 23 named content domains that together produce 120 scored questions. PSI may also insert 1-10 unscored experimental items that look identical to scored questions and count against your five-hour time limit, so every domain deserves real preparation, not guesswork.
Nevada does not publish these 23 domains as equally weighted. Instead, the March 25, 2026 PSI bulletin assigns each domain a specific number of scored questions, ranging from as few as 3 items up to 10 items. Understanding this allocation is the single most useful thing you can do before opening a textbook, because it tells you exactly where your study hours produce the most return. If you want the full mechanics of scoring and eligibility before diving into domains, the NV-C1 Passing Score guide and NV-C1 Requirements breakdown are useful companion reads.
The Four Heavyweight Domains
Four domains tie for the largest share of the exam at 8 items each, and one domain stands alone as the single largest content area at 10 items. These five domains together account for 42 of the 120 scored questions - over a third of the entire exam.
Domain 11: Drain, Waste, and Vents (10 items)
The largest domain on the exam. Expect questions on trap arm limits, vent sizing, wet venting, and drainage fixture units as codified in UPC 2018.
- Sizing DWV piping by fixture unit load
- Vent placement relative to trap weirs
- Combination waste and vent systems
Domain 2: Gas Systems (8 items)
Gas piping sizing, appliance connections, and venting clearances draw heavily on NFPA 54 (2012), one of the five references you'll have open during the exam.
- Pipe sizing tables and demand calculations
- Shutoff valve placement and appliance connectors
- Venting categories for gas-fired equipment
Domain 9: Water Supply (8 items)
Covers potable water distribution, pipe sizing, and pressure requirements referenced in UPC 2018.
- Fixture unit demand and pipe sizing charts
- Water hammer arrestors and pressure-reducing valves
- Cross-connection basics that overlap with Domain 12
Domain 13: Traps and Interceptors (8 items)
Focuses on trap seal requirements, grease interceptors, and sizing criteria for specialized waste applications.
- Minimum and maximum trap seal depths
- Grease interceptor sizing methods
- Acid and oil interceptor code triggers
Domain 14: Isometric Analysis/Plumbing Mathematics (8 items)
This is the most calculation-heavy domain. Expect isometric drawing interpretation, fixture unit math, and pipe slope calculations, which is exactly where a permitted silent, nonprinting, nonprogrammable calculator becomes essential.
- Reading isometric riser diagrams
- Calculating drainage and vent sizing from fixture counts
- Slope and offset math for DWV runs
Key Takeaway
Allocate your heaviest study blocks to Drain, Waste, and Vents, Gas Systems, Water Supply, Traps and Interceptors, and Isometric Analysis/Plumbing Mathematics - together they represent 35% of all scored questions.
Mid-Weight Domains You Cannot Skip
Below the top five, a second tier of domains carries between 5 and 7 items each. These are not throwaway categories - collectively they still represent a meaningful chunk of your final score.
Domain 18: General Plumbing Requirements (7 items)
Covers permitting, inspection triggers, and administrative code provisions that apply broadly across plumbing installations.
Domain 6: Water Heaters/Venting (6 items)
Tank and tankless water heater installation clearances, relief valve sizing, and venting configurations.
Domain 23: Chilled Water Piping (6 items)
Insulation requirements, pipe sizing for cooling loads, and support spacing for chilled water distribution systems.
Domain 10: Hangers and Supports (5 items)
Spacing intervals for various pipe materials and support types across horizontal and vertical runs.
Domain 15: Safety (5 items)
Jobsite safety provisions relevant to plumbing and heating installation work.
Domain 19: Fire Sprinklers (5 items)
Basic sprinkler system requirements drawing on NFPA 13 (2019), one of the five admitted exam-room references.
Domain 20: Storm Drainage (5 items)
Roof drain sizing, area drains, and secondary drainage provisions under UPC 2018.
If you're weighing how much total effort these mid-weight domains deserve relative to the "big five," the How Hard Is the NV-C1 Exam guide walks through relative difficulty across domain tiers in more depth.
Lighter Domains That Still Cost Points
The remaining domains carry between 3 and 4 items each. Individually small, but nine of these lighter domains together still total roughly 33 questions - more than a quarter of the exam.
4-Item Domains
Boilers, Cleanouts, Fixtures and Equipment, Backflow, Joints and Connections, and Solar each carry 4 items. Backflow overlaps conceptually with Water Supply, so studying them together is efficient.
3-Item Domains
Hydronics, Piping/Valves/Controls, Sheet Metal, Industrial Piping, and Breathing Systems for Firefighters each carry 3 items. NFPA 58 (2014) supports propane-related questions that may surface across several of these lighter domains.
Complete Domain-by-Domain Item Allocation
Here is the full 23-domain breakdown as published in the PSI bulletin, ordered exactly as the Board and PSI present it.
| # | Domain | Scored Items |
|---|---|---|
| 1 | Boilers | 4 |
| 2 | Gas Systems | 8 |
| 3 | Cleanouts | 4 |
| 4 | Fixtures and Equipment | 4 |
| 5 | Hydronics | 3 |
| 6 | Water Heaters/Venting | 6 |
| 7 | Piping, Valves, and Controls | 3 |
| 8 | Sheet Metal | 3 |
| 9 | Water Supply | 8 |
| 10 | Hangers and Supports | 5 |
| 11 | Drain, Waste, and Vents | 10 |
| 12 | Backflow | 4 |
| 13 | Traps and Interceptors | 8 |
| 14 | Isometric Analysis/Plumbing Mathematics | 8 |
| 15 | Safety | 5 |
| 16 | Joints and Connections | 4 |
| 17 | Solar | 4 |
| 18 | General Plumbing Requirements | 7 |
| 19 | Fire Sprinklers | 5 |
| 20 | Storm Drainage | 5 |
| 21 | Industrial Piping | 3 |
| 22 | Breathing Systems for Firefighters | 3 |
| 23 | Chilled Water Piping | 6 |
| Total | 120 |
This proportional breakdown is exactly what powers a well-built NV-C1 practice test - practicing question sets that mirror the 10-item weight of Drain, Waste, and Vents alongside the 3-item weight of Industrial Piping gives you realistic exposure rather than an evenly distributed, unrealistic study experience.
Question Format, References, and Exam-Room Rules
The NV-C1 trade exam is computer-administered and open-book, but "open-book" here has strict boundaries. Only five references are permitted in the testing room: UPC 2018, UMC 2018, NFPA 54 (2012), NFPA 58 (2014), and NFPA 13 (2019). Other study materials referenced in the bulletin, including secondary study guides, cannot be brought into the room - they exist for preparation only.
- Advance highlighting, underlining, and permanent tabs in your reference books are allowed.
- Handwritten notes, loose papers, and temporary sticky tabs are prohibited.
- A silent, nonprinting, nonprogrammable calculator without an alphabetic keyboard is allowed - critical for Domain 14's math-heavy questions.
- You have five hours to answer 120 scored questions plus up to 10 unscored experimental items.
Candidates who fail must wait two weeks before retesting, and three failed attempts void the application entirely - making domain-by-domain preparation far cheaper than repeated retest fees. For a broader look at how tough this exam actually is relative to its content spread, see the NV-C1 Pass Rate data review.
Mapping Domains to a Study Schedule
Rather than studying all 23 domains in the order they're listed, sequence your review by weight so the heaviest-scoring material gets the most repetition before test day.
Heavyweight Domains
- Drain, Waste, and Vents (10 items)
- Gas Systems (8 items)
- Water Supply (8 items)
Traps, Interceptors, and Math
- Traps and Interceptors (8 items)
- Isometric Analysis/Plumbing Mathematics (8 items)
- Practice calculator use for slope and fixture unit problems
Mid-Weight Systems
- General Plumbing Requirements (7)
- Water Heaters/Venting (6)
- Chilled Water Piping (6)
- Hangers and Supports, Safety, Fire Sprinklers, Storm Drainage (5 each)
Lighter Domains and Full Review
- Boilers, Cleanouts, Fixtures and Equipment, Backflow, Joints and Connections, Solar (4 each)
- Hydronics, Piping/Valves/Controls, Sheet Metal, Industrial Piping, Breathing Systems for Firefighters (3 each)
- Full-length timed practice run under five-hour conditions
This sequencing approach is covered in more detail, along with reference-book tabbing strategy, in the NV-C1 Study Guide for passing on your first attempt. If you're still confirming eligibility before committing to a study calendar, check the NV-C1 Exam Dates and scheduling guide for how Board approval timing interacts with PSI scheduling windows.
Key Takeaway
Build your final week around a full timed practice session using only the five permitted references, since simulating the open-book, five-hour format matters as much as memorizing domain content.
Frequently Asked Questions
Drain, Waste, and Vents is the largest single domain with 10 scored questions, more than any other of the 23 content areas.
No. Item counts range from 3 to 10 per domain across the 120 total scored questions, with Gas Systems, Water Supply, Traps and Interceptors, and Isometric Analysis/Plumbing Mathematics each carrying 8 items.
No. Only UPC 2018, UMC 2018, NFPA 54 (2012), NFPA 58 (2014), and NFPA 13 (2019) are permitted, with advance highlighting and permanent tabs allowed, but handwritten notes and loose papers are prohibited.
No. The Contractor Management Survey (CMS) is a separate exam with its own 75% passing standard and is not part of the 23 trade domains covered here.
PSI may insert 1-10 unscored experimental questions anywhere across the exam, and since they are indistinguishable from scored items, every domain should be studied as if all its questions count.
For a deeper dive into what this certification unlocks professionally once you've mapped every domain, the NV-C1 Salary Guide and Is the NV-C1 Certification Worth It analysis connect domain mastery to real licensing outcomes. When you're ready to test your recall against this exact 23-domain weighting, a full-length NV-C1 practice test is the fastest way to find weak spots before exam day.