NH Journeyman Plumber common mistakes
NH Journeyman Plumber · Understand the traps and how to avoid them.
Answering code questions from memory of the IPC or a neighboring state's code instead of the New Hampshire amendments, so answers about trap seal protection, fixture unit values, or vent sizing reflect the model code rather than what New Hampshire adopted.
Most candidates train on generic IPC study material and national exam prep, and the New Hampshire Plumbing Code consists of the model code as amended by state rules; the amendments are where the state-specific questions live, and candidates underestimate how many items test the amendments.
What to do instead
Build a one-page amendment log while studying: for each chapter of the adopted code, note every New Hampshire change (scope of licensure, local enforcement, adopted editions, any state-specific sizing or installation rules) and cite the rule number. Before the exam, re-read the amendment log rather than the model code text, and for any practice question ask 'is this the model code answer or the New Hampshire answer?'
Treating the plumbing statutes and administrative rules as background reading and skipping them, then missing items on licensure tiers, apprentice supervision ratios, continuing education, permit and inspection requirements, and grounds for discipline.
Candidates assume the exam is purely technical and that law items are a small fraction; in fact state-specific legal items are easy points that require memorization rather than calculation, and candidates who never read the statute and rules chapters guess on them.
What to do instead
Study the licensing statute and the board's administrative rules as a separate block with the same rigor as drainage. Make flashcards for: license categories and their scope, supervision requirements for apprentices and journeymen, renewal and continuing education requirements, permit issuance and inspection notice rules, and the list of disciplinary grounds. Recite the numbers (hours, ratios, fees, deadlines) aloud until automatic.
Sizing drainage and vent piping by picking the pipe size that 'looks right' for the fixture count instead of using drainage fixture units, developed length, slope, and the fixture-unit-to-vent-size tables, and failing to check that the chosen size is permitted for the actual slope and branch length.
Field experience teaches rules of thumb ('two-inch for a bathroom group') that work on small residential jobs but fail on exam items with long developed lengths, multiple branches, or unusual fixture combinations; candidates also forget that a size that carries the fixture units may still be undersized for the developed length at the given slope.
What to do instead
Practice with the actual tables until the workflow is automatic: convert fixtures to drainage fixture units, sum per branch and stack, determine slope, compute developed length, then read the allowable fixture units for each candidate size and verify the vent size from the vent tables. Do at least twenty drill problems with deliberately awkward inputs (long runs, many water closets, combined branches) and write out each step so the method, not the intuition, drives the answer.
Confusing vent types and their installation limits, treating a circuit vent, island fixture vent, wet vent, combination waste and vent, air admittance valve, and individual vent as interchangeable, and missing the restrictions each carries.
The venting chapter is the most rule-dense part of the code, and candidates memorize definitions without the conditions: which fixtures may be wet-vented together, how many fixtures a circuit vent can serve, what slope and length limits apply to an island vent, and where air admittance valves are prohibited or limited.
What to do instead
Make a comparison matrix with one row per vent type and columns for what it connects, maximum fixtures served, size rules, slope and length limits, prohibitions, and required cleanouts or access. Fill it from the code text with section citations, then answer scenario questions by locating the row first and the code section second. Pay particular attention to wet vent bathroom group rules and to the conditions under which an air admittance valve is allowed.
Ignoring the distinction between minimum fixture flow/pressure requirements and pipe sizing for pressure loss, choosing pipe diameter from a fixture-unit chart alone without checking available pressure, elevation loss, and developed length through fittings.
Candidates conflate the drainage fixture-unit method with water supply sizing; water supply sizing requires estimating demand in fixture units or gallons per minute, converting to equivalent length including fittings, and verifying residual pressure at the most remote fixture. Study guides often present only the fixture-unit table, so the pressure-check step is skipped.
What to do instead
Work water supply problems in a fixed sequence: list fixtures and their minimum required flow and pressure, sum demand, measure developed length, add fitting equivalent lengths, select a candidate size from the table, then compute friction loss and subtract elevation and meter loss to confirm residual pressure at the farthest fixture. Practice at least ten problems where the table-suggested size fails the pressure check so the second step becomes habitual.
Answering water heater items with generic appliance knowledge and missing the plumbing-specific requirements: temperature and pressure relief valve sizing and discharge piping, thermal expansion control, seismic or support requirements, combustion air, and venting of gas-fired heaters.
Water heaters sit at the intersection of the plumbing code and the fuel gas code, and candidates study them briefly as 'just a tank'. The relief valve discharge pipe rules (material, termination, no trapping, no reduction in size) and the combustion air and venting requirements for gas appliances generate many items that reward specific code reading.
What to do instead
Create a one-page water heater checklist covering relief valve rating relative to tank input, discharge pipe material and termination, pan and drain requirements, thermal expansion and backflow prevention on the cold inlet, combustion air method and sizing, and vent connector and chimney requirements. For each item, write the code section. Then answer practice questions by running the checklist rather than recalling a single fact.
Missing the fixture-fitting details that distinguish a code-compliant installation: water closet flush volume and fixture replacement rules, backflow protection for hose bibs and supply connections, air gaps versus vacuum breakers, slip joint and trap arm limits, and accessibility clearances.
Candidates focus on pipe and vent sizing and treat fixtures as simple, so they overlook the fitting-level requirements: maximum trap arm length by trap size, the required air gap for a fixture outlet, when a vacuum breaker is acceptable versus an air gap, and the water efficiency limits that apply when fixtures are replaced.
What to do instead
Study the fixtures and fixture fittings chapter by fixture type, writing for each one the trap size, trap arm limit, required backflow protection, water consumption limit, and clearance or accessibility requirement. Pay special attention to the difference between an air gap and a vacuum breaker and to the conditions under which each is permitted, and to the rules that apply when replacing fixtures in existing buildings.
Sizing gas piping from a single fixture or appliance input rating without applying the longest-length method, diversity factors, and the specific gravity and pressure adjustment factors, and without verifying the pressure drop allowed for the system pressure.
Gas sizing tables are indexed by inlet pressure, pressure drop, and gas specific gravity, and candidates use the wrong table or forget that the longest run from the meter determines the capacity for every branch. They also forget to convert appliance input ratings to cubic feet per hour using the heating value of the gas.
What to do instead
Drill the method: convert each appliance input to cubic feet per hour, measure the longest run from the meter to the farthest appliance, select the table matching the system pressure, allowable drop, and gas specific gravity, then size each segment for the total load downstream of it using its own length. Practice with a manifold serving several appliances so the segment-by-segment logic is exercised, and always state the table conditions before reading a value.
Handling storm drainage as if it were sanitary drainage, applying sanitary slope and sizing rules, and missing the separate requirements for roof drains, leaders, overflow scuppers or secondary drainage, and the prohibition on connecting storm drainage to the sanitary system.
Storm drainage appears in the same code chapter as sanitary drainage, so candidates skim it and assume the same rules apply; they then miss items about primary and secondary roof drainage, the sizing of leaders based on rainfall rate, and the trap and cleanout requirements specific to storm systems.
What to do instead
Treat storm drainage as its own study unit: rainfall rate assumptions, roof drain and leader sizing by area and rate, secondary drainage requirements, conductor and horizontal storm pipe sizing and slope, trap requirements, and the strict separation from sanitary drainage. Write out the differences from sanitary drainage side by side and answer storm questions only after identifying which system the item describes.
Rushing the code-reference questions and answering from a recalled phrase instead of locating the actual section, then missing the effect of an exception, a footnote, or a defined term that reverses the answer.
The exam is open to code reference in many jurisdictions and the items are written so that the correct answer depends on a specific exception or definition; candidates who answer from memory choose the general rule and miss the exception, and candidates who do look it up often stop at the first matching sentence without reading the exception below it.
What to do instead
Practice a lookup protocol: identify the key term, go to the index or table of contents, find the section, read the entire section including exceptions and footnotes, and check the definitions chapter for any term in the question that has a code definition. Time yourself so lookups stay under ninety seconds, and on every practice question write down the section number you used; if you cannot cite one, mark the question for review rather than guessing.