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ID Plumber: Fixtures, Fixture Fittings, and Water Heaters

ID Plumber · Work through your exam, one topic at a time.

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Fixtures, Fixture Fittings, and Water Heaters

Setting fixtures

Fixture questions test dimensional rules and approvals. A water closet is set with its centerline at least 15 inches from a sidewall or partition and at least 15 inches from a bathtub or shower, with code-required clear space in front; adjacent water closets are typically spaced 30 inches on center. Compartments are sized by the code and, where accessible, by the accessibility standard. Fixtures must be listed and installed per their listing, with slip-joint connections accessible and floor drain trap seals maintained by primers where evaporation occurs.

Fixture fittings

  • Flushometer valves need higher residual pressure than tank-type water closets, so a low-pressure building may be limited to tanks.
  • Faucets and shower valves must be protected against backflow by the listed device (vacuum breaker, integral air gap).
  • Tempered water limits apply to public lavatories and bathing facilities to prevent scalding.

Water heaters

  • A temperature-and-pressure relief valve is required, listed for the heater, with no cap or plug, and no valve between the heater and the relief valve.
  • The discharge pipe is full size, runs by gravity, has no trap, uses material rated for the temperature, terminates within 6 inches of the floor or outside, and the outlet end is not threaded.
  • A closed system created by a check valve or pressure-reducing valve needs thermal expansion control.
  • Venting, combustion air, and clearance to combustibles follow the appliance listing.

Worked example

An inspector finds a T&P discharge terminating 4 feet above the floor with a threaded cap on the end. Two defects: the termination must be within 6 inches of the floor (or discharge outdoors), and the end must not be threaded so it cannot be capped. Both are common exam distractors phrased as "minor field issues."

Traps

  • Sizing a flushometer installation on tank-type pressure assumptions.
  • Ignoring thermal expansion after adding a PRV.
  • Assuming a relief valve is optional on a small heater.