Plumbing Systems and Fixtures
Plumbing Systems and Fixtures
This domain covers fixture selection, installation clearances, trim, and the appliances that serve fixtures-especially water heaters. The exam expects you to know minimum clearances, fixture-unit values, and the safety devices that must be installed with storage water heaters.
Fixture clearances and installation
- A water closet needs at least 15 in from its centerline to any sidewall or fixture and at least 21 in of clear space in front of the bowl. A 30 in clear width is the practical minimum compartment.
- Lavatories, sinks, and showers must be installed level, secured to framing, and sealed at the wall and rim.
- Fixture-unit (FU) values are used for pipe sizing: a tank-type water closet is commonly 3 FU, a lavatory 1 FU, and a bathtub or shower 2 FU. Use the adopted code table, not memory, for final sizing.
Water heaters
- The temperature-and-pressure (T&P) relief valve must be located in the top 6 in of the tank and must not be capped, plugged, or reduced in size.
- The discharge pipe must be the full size of the valve outlet, terminate 6 in above the floor or at an approved drain, and have no valve or thread at the end.
- On a closed system, install a thermal expansion tank. Strap the heater per seismic requirements, and install a drain pan where leakage would cause damage.
Worked example
A 50 gal heater has a 3/4 in T&P valve. The installer runs 1/2 in copper from the valve to a floor drain and caps the end. Identify the violations. The discharge is reduced from 3/4 in to 1/2 in-not allowed; the end is capped-not allowed because the valve must relieve freely; and the termination at the drain must be visible and 6 in above the floor or properly piped. Correct the job with full-size 3/4 in pipe, no cap, and an air gap at the drain.
Traps that cost marks
- Capping or plugging a T&P discharge to stop a drip instead of repairing the cause.
- Omitting an expansion tank on a closed system with a backflow preventer.
- Installing a water heater without seismic strapping or a required pan.
- Using a slip-joint connection on a T&P discharge.
- Measuring water-closet clearance from the tank instead of the bowl centerline.