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Tennessee CMC-A Mechanical Plumbing Practice Exam

What This Practice Exam Covers

The Tennessee CMC-A Mechanical Plumbing licensing exam consists of 110 questions with a 295-minute time limit. You need a 73% (80/110) to pass. The exam spans nine topic areas, from hands-on math and isometric layout to code-based rules on drainage, gas piping, and OSHA safety.

This practice exam gives you two options:

• Free practice exam: 10 questions per attempt, drawn from a limited pool. Retake it as many times as you like to get a feel for question style, phrasing, and format — at no cost.
• Full practice exam (paid): Mirrors the real exam exactly — 110 questions, 295-minute clock, and drawn from a pool of 623+ questions. Because the pool is large, no two attempts produce the same exam. This is the closest simulation available before exam day.

Start with the free exam to get oriented, then use the full practice exam for serious, timed preparation.

What You'll Be Tested On

General Knowledge and Math — 14 items

This is the largest single topic and one of the most calculation-intensive. Expect arithmetic operations applied to plumbing scenarios, unit conversions between English and metric systems, and geometry — area and volume of pipes, tanks, and rooms. The Pythagorean theorem appears in right-triangle problems, and you must also solve pipe offset problems using the specific angle constants (0.707 for 45°, 0.577 for 60°, 2.613 for 22½°, etc.). Water pressure, head, and force calculations — such as converting feet of head to psi (0.433 psi per foot) — are tested here. Bring solid arithmetic fluency; these questions reward candidates who have drilled the formulas until they are automatic.

General Requirements — 10 items

This topic covers administrative and structural provisions, backflow prevention rules, approved pipe materials and support spacing, joint and connection methods, storm drain requirements, and testing procedures. Candidates are tested on Table 308.5 for pipe support intervals and on testing methods per IPC 2021 Sections 312.5, 312.10.1, and 312.10.2. Know which materials are approved for which applications, and understand how different joint types are tested and inspected.

Water Supply and Distribution — 10 items

Potable water protection and cross-connection control dominate this topic. You must know which backflow prevention assemblies are required for specific hazard levels, pipe materials approved for water service versus interior distribution, and the rules governing pressure-reducing valves and booster systems (IPC 2021, Section 604.8 and Table 604.3). Hot water supply requirements — including thermal expansion control and minimum temperatures — appear regularly. System sizing using fixture units and the segmented loss method from IPC Appendix E is also fair game.

Fixtures, including Water Heaters — 6 items

Despite the lower item count, this topic demands precision. You must know minimum fixture counts by occupancy from IPC 2021 Table 403.1, clearance requirements for fixture installation, and the rules for shower valves and temperature-limiting devices. Water heater safety is heavily represented: relief valve requirements, discharge piping rules per IPC 2021 Section 504.6, energy shutoff provisions per Section 504.3, and access and location requirements. Confusing the relief valve discharge rules with other safety piping requirements is a common error.

Drain, Waste, and Vent Systems — 28 items

This is the single heaviest topic on the exam — more than one in four questions. You need command of drainage fixture unit (DFU) values from IPC 2021 Table 709.1, how unlisted fixtures are assigned DFU values per Section 709.2 and Table 709.2, horizontal pipe slope requirements, and the full cleanout placement and sizing rules (Sections 708.1.1 through 708.1.10). Trap requirements, prohibited trap types, and trap seal protection are tested in depth. Indirect and special waste provisions — air gaps, air breaks, standpipe heights — round out this section. Budget study time proportionally here; 28 items can make or break your score.

Traps, Cleanouts, and Interceptors — 6 items

This focused topic tests trap seal depth requirements (minimum 2 inches, maximum 4 inches), prohibited trap configurations, and grease interceptor sizing and installation per IPC Sections 1003.3.1, 1003.3.2, 1003.4.2.2, and 1003.6. Know what constitutes a "prohibited trap" — including S-traps and bell traps — and understand how trap seal protection methods such as air admittance valves work.

Isometric Analysis — 20 items

Twenty questions — almost one in five — require you to calculate pipe lengths from isometric drawings. This includes center-to-center and end-to-end pipe lengths, fitting allowances for threaded, copper, PVC, and welded fittings, and 45° offset calculations using the 1.414 diagonal constant and the 0.707 travel constant. Other fitting angles (60°, 22½°, 11¼°, 72°) each have their own constants you are expected to apply correctly. Three-pipe diagonal assemblies, rolling offsets, and true offsets require multi-step calculation sequences drawn from Mathematics for Plumbers and Pipefitters. A single wrong constant or missed fitting allowance cascades through the entire answer.

Gas Appliances and Piping — 12 items

Tested under the International Fuel Gas Code 2021. Approved gas piping materials — including metallic pipe, copper tubing, CSST, and polyethylene — are tested alongside fittings and joining methods. Pipe sizing uses the longest-length, branch-length, or hybrid-pressure methods from IFGC Appendix B and D. Pressure testing and leak check procedures are tested directly. Combustion air calculations for indoor, outdoor, and combination methods appear frequently, including the specific volume-based formulas from IFGC Sections 304 and 305.

OSHA Safety — 4 items

Four questions from a broad safety framework. Expect questions on fall protection (guardrail heights, personal fall arrest system requirements per 29 CFR §1926.502), excavation cave-in protection and competent-person inspection requirements per 29 CFR 1926.651(c)(2), confined space entry and permit requirements per 29 CFR §1926.1204(e)(3), PPE provision and payment, fire extinguisher requirements per 29 CFR 1926, Subpart F, §1926.150(c)(1)(vi), and noise exposure limits per 29 CFR §1926.52(a). Though only four items, they are often straightforward — don't leave free points on the table.

Worked Sample Questions

Sample 1 — Drain, Waste, and Vent Systems

Question: The size of drainage piping shall not be reduced in the direction of flow. Which of the following is NOT considered a reduction in pipe size?

• A. A 3-inch-to-2-inch reducer fitting on a horizontal branch
• B. A 4-inch by 3-inch water closet flange
• C. A 3-inch-to-2-inch bushing on a building drain
• D. A 4-inch-to-3-inch reducer on a vertical waste stack

Correct Answer: B

A 4-inch by 3-inch water closet flange is specifically listed as an exception under IPC 2021, Section 704.2 — it is not treated as a prohibited reduction in the direction of flow. Options A, C, and D all describe actual reducer fittings applied to horizontal branches, building drains, or stacks, all of which violate the general rule. The code carves out the water closet flange because the toilet horn fits a 4-inch flange while the downstream piping typically runs 3 inches — a deliberate, permitted configuration.

Source: IPC 2021, Section 704.2

Sample 2 — Isometric Analysis / DFU Values

Question: For a fixture not listed in the drainage fixture unit table, what determines its DFU value?

• A. The fixture's water supply connection size
• B. The fixture's outlet size, referenced to a DFU-by-trap-size table
• C. The fixture's total water consumption per cycle
• D. The fixture's mounting height above the finished floor

Correct Answer: B

When a fixture does not appear in IPC 2021 Table 709.1, Section 709.2 directs you to Table 709.2, which assigns DFU values based on trap (outlet) size — not supply size, consumption, or mounting height. The minimum trap size for an unlisted fixture equals the size of its drainage outlet but cannot be less than 1¼ inches. This is a classic misdirection question: candidates who confuse supply connection size with drain outlet size will select A instead of B.

Source: IPC 2021, Section 709.2

Sample 3 — Fixtures, including Water Heaters

Question: When shutting down an electric hot water supply system, how must the system be disconnected from its energy supply?

• A. By means specified in NFPA 70
• B. By activation of the temperature relief valve
• C. By a separate valve installed on the hot water distribution line
• D. By closing the cold water supply valve

Correct Answer: A

IPC 2021 Section 504.3 requires that electric hot water systems be disconnected from their energy supply by means that comply with NFPA 70 (the National Electrical Code). For gas-fired systems the code requires a separate fuel shutoff valve — not a water valve or the T&P relief valve. Options B, C, and D would be dangerous or ineffective: the relief valve is a safety device, not a disconnect, and water supply valves do not de-energize electrical equipment.

Source: IPC 2021, Section 504.3

How to Read Your Score

The passing score is 73%, which equals approximately 80 correct answers out of 110.

Treat your first practice attempt as a diagnostic, not a verdict. Most candidates underperform early — that result tells you where to concentrate study effort, not whether you will pass. A topic-by-topic breakdown is far more useful than the overall percentage: if you score 90% on OSHA Safety (4 items) but 55% on Drain, Waste, and Vent Systems (28 items), your priority is obvious.

Scoring 75–80% on a first full practice attempt suggests you are in the right range but not yet comfortable with the margin — exam-day nerves, unfamiliar phrasing, and time pressure all work against you. Scoring below 70% consistently means gaps in foundational knowledge, not just test-taking strategy. Scoring above 85% across multiple unique attempts from the 623+ question pool is a strong readiness signal.

Retake the full practice exam on different days with a fresh question set. Because the pool is large, repeating the exam tests recall, not memorization of specific questions.

Where Candidates Lose Points

Isometric calculations (20 items): Using the wrong angle constant is the single most common calculation error. Candidates mix up the 1.414 diagonal multiplier and the 0.707 offset constant for 45° fittings, or forget to subtract fitting allowances from center-to-center measurements to get end-to-end pipe cut lengths. One wrong constant corrupts every downstream number.

DFU table lookup (Drain, Waste, and Vent — 28 items): Candidates assign DFU values from memory rather than the correct table, especially for unlisted fixtures. Section 709.2 and Table 709.2 exist for exactly this case — skipping them costs points.

Direction-of-flow reductions: Section 704.2 questions trip up candidates who don't know the water closet flange exception cold.

Gas pipe sizing method selection (12 items): Choosing the wrong IFGC Appendix (B vs. D) for the pressure regime — or confusing the longest-length method with the branch-length method — leads to wrong pipe sizes.

Water heater discharge piping rules: Candidates confuse relief valve discharge pipe sizing and termination requirements with general hot water piping rules.

Time management: At 295 minutes for 110 questions, you have about 2 minutes 41 seconds per question. Multi-step isometric and math problems can eat 5–6 minutes each. Candidates who don't pace themselves run short on time in the final 20–30 questions.

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