NBOPE/IAPMO Master Plumber key terms

A dimensionless value assigned to a plumbing fixture reflecting its probable peak flow demand, used to size water supply pipes and drainage systems rather than counting fixtures alone.

A loading value expressing a fixture's hot and cold water demand relative to a lavatory, used with probability curves to determine minimum pipe size for distribution systems.

A loading value expressing the rate at which a fixture discharges waste into a drainage system, used to size branches, stacks, and building drains.

A probability-based chart relating total fixture units to probable peak demand in gallons per minute, forming the basis for sizing water distribution piping serving many fixtures.

An unobstructed vertical distance through open air between a potable water outlet and the flood-level rim of a receiving vessel, providing the highest degree of cross-connection protection.

The unwanted reversal of water flow in a piping system, caused by backsiphonage or backpressure, which can draw contaminants into the potable supply.

Backflow caused by negative or subatmospheric pressure in the supply piping, pulling nonpotable liquids into the potable system through a cross connection.

Backflow caused by downstream pressure exceeding supply pressure, such as from a boiler, pump, or elevated tank connected to the potable system.

Any actual or potential physical connection between a potable water system and a source of contamination or pollution, enabling backflow into drinking water.

A testable backflow preventer with two independently acting check valves and a relief valve between them that discharges if either check leaks, used for high-hazard protection.

A testable backflow preventer consisting of two independently acting check valves, approved only for low-hazard protection where contamination risk is not present.

A device admitting air into piping to break a vacuum and prevent backsiphonage, available as atmospheric or pressure-type units on hose bibbs and flush valves.

The edge of a receptacle from which water would overflow onto the floor, used as the reference elevation for setting air gaps and backflow device heights.

A drainline separation where waste discharges into a receptacle through open air below the flood-level rim, preventing sewage backup from contacting fixtures or equipment.

The depth of water retained in a trap, typically two to four inches, that blocks sewer gas from entering a building through the fixture drain.

A U-shaped fitting at a fixture drain that holds a water seal while allowing waste to pass, required at each fixture except where a listed trap integral to the fixture is provided.

A vertical pipe providing air to a drainage system and relieving pressure so trap seals are not siphoned, extending through the roof or connecting to a common vent.

The extension of a soil or waste stack above the highest horizontal branch, serving as the vent for the stack and typically terminating outdoors above the roof.

A one-way valve that opens to admit air into drainage piping when pressure drops and seals under positive pressure, permitted only where the code allows in lieu of a vent.

A vertical pipe conveying toilet and similar heavy-waste discharge from fixtures to the building drain, distinguished from a waste stack carrying other fixtures.

The lowest piping of a drainage system receiving waste from inside the building and conveying it to the building sewer, terminating at or outside the foundation wall.

The piping that carries sewage from the building drain to the public sewer or private disposal system, beginning outside the building foundation.

The fall of horizontal drainage piping expressed in inches per foot, required so solids move with the flow; typical minimums are one-quarter inch per foot for small pipe.

The pipe segment between a trap and its vent connection, limited in developed length by pipe size to prevent self-siphonage of the trap seal.

A receptacle receiving liquid waste through an air break, used for fixtures such as sterilizers or ice machines that must not be directly connected to the drainage system.

Waste requiring treatment or special handling before entering the drainage system, including corrosive, greasy, or high-temperature discharges from commercial and medical processes.

A receptacle that slows flow so fats, oils, and grease separate and float for removal, required for commercial kitchens before discharge to the building drainage system.

A system collecting and conveying rainwater and surface runoff from roofs, yards, and paved areas to a storm sewer or approved disposal point, separate from sanitary drainage.

The drain, typically with a strainer and flat or low dome, that carries normal rainfall from a roof, sized using rainfall intensity and roof area.

A backup roof drainage means, such as a separate drain or scupper set above the primary drain, that carries water if the primary system is blocked.

The increase in water volume as it is heated in a closed system, which raises pressure and requires a relief valve, expansion tank, or other approved control.

A vessel with a captive air charge that absorbs the volume increase of heated water in a closed system, limiting pressure rise and protecting piping and fixtures.

A safety device that opens to discharge water when a water heater exceeds a set temperature or pressure, preventing tank rupture and requiring a full-size discharge pipe.

Air supplied to fuel-burning appliances for burning fuel and dilution, required in adequate volume from outdoors or adjacent spaces per code.

Piping, tubing, and fittings conveying natural gas or propane to appliances, installed with approved materials, sizing, and shutoff valves per the fuel gas code.

A drip leg installed at the appliance connection to collect debris and condensate before it reaches gas controls, required at the outlet of the gas supply.

A passage conveying products of combustion from an appliance to the outdoors, which must be sized, pitched, and terminated to maintain safe draft.

A three-dimensional representation of piping layout drawn on angled axes, showing pipe runs, fittings, and sizes so installers can plan routing and material takeoffs.

A schematic elevation showing vertical relationships of stacks, drains, vents, and fixtures in a building, not drawn to scale but used to check system arrangement.

A top-down drawing showing fixture locations, pipe routes, and dimensions on a floor, used with riser and isometric drawings to interpret a plumbing system.

Official authorization to install, alter, or repair plumbing work, obtained before work begins and typically requiring plans, fees, and inspection scheduling.

An official examination of plumbing work at defined stages, such as rough-in and final, to verify compliance before the system is covered or placed in service.

The inspection of piping, vents, and connections made before walls, floors, or ceilings are closed, allowing verification of materials, slope, and support.

A document issued after final inspections confirm that a building and its systems comply with approved plans and codes, permitting legal occupancy.

Design and installation of medical gas, vacuum, purified water, and specialty drainage systems in hospitals and clinics, subject to additional standards beyond the plumbing code.

Piping conveying oxygen, medical air, nitrous oxide, or vacuum in health care facilities, installed, brazed, and tested under special standards by qualified personnel.

A written modification to the contract scope, price, or schedule signed by the owner and contractor, documenting work added or deleted after the contract is executed.

A contractor's priced offer to perform specified work, prepared from takeoffs, labor rates, material costs, and markups for overhead and profit.

A systematic count and measurement of materials and fixtures from drawings, forming the basis for an estimate and bid.

A written record of incomplete or deficient work identified near project completion, which the contractor must correct before final payment and acceptance.

An appliance that heats and stores potable water for domestic use, requiring a listed relief valve, seismic or thermal protection as applicable, and proper venting.

The network of pipes, valves, and fittings delivering potable water from the meter or source to fixtures at adequate pressure and flow, sized by fixture units.

An organized effort to identify hazards, require appropriate backflow preventers, and test and maintain them so the potable supply remains protected.