NITC Master Plumber key terms

A dimensionless measure of the probable load a plumbing fixture places on the drainage or supply system, based on its flow rate and use frequency. Fixture units let designers size pipes by combining dissimilar fixtures into one comparable demand figure.

The fixture-unit rating assigned to a fixture for sizing sanitary drainage piping, reflecting its discharge volume and drain size. A water closet typically rates higher than a lavatory, so DFU totals drive branch and building drain sizing.

A probability-based method that converts total fixture units into estimated peak demand in gallons per minute, accounting for the statistical likelihood that not all fixtures run simultaneously. It underpins demand tables used to size water distribution piping.

The maximum expected rate of water flow a system must deliver during its busiest period, usually expressed in gallons per minute. Supply mains, meters, and pressure-boost equipment are sized against this value rather than average use.

The lowest horizontal pipe inside a building that receives soil and waste from branch drains and conveys it to the building sewer. It ends at the building wall or foundation line, where the building sewer begins.

The pipe carrying sewage from the building drain's termination point to the public sewer or private disposal system. It lies outside the building footprint and is typically governed by both plumbing and municipal requirements.

A vertical drainage pipe that receives discharge from water closets and carries it downward to the building drain. It must extend through the roof or connect to a venting arrangement to prevent trap siphonage.

A vertical vent pipe that provides air to one or more drainage stacks, protecting trap seals from pressure fluctuations. It extends above the roof and may serve as a common vent for several fixtures.

The depth of water retained in a fixture trap that blocks sewer gas from entering the building. Codes set a minimum depth, commonly two to four inches, and require protection from siphonage and evaporation.

A one-way mechanical valve that admits air into drainage piping when negative pressure develops and seals shut afterward, venting a fixture without a roof penetration. Codes restrict its use and require access for maintenance.

A vent pipe that also serves as a drain for fixtures on a floor above the fixtures it vents. Its use is limited by code because simultaneous drainage and venting can compromise trap seal protection.

An accessible fitting with a removable plug or cover that allows a drain snake or jetting tool to clear blockages in drainage piping. Codes specify locations, spacing, and required accessibility for maintenance.

The downward pitch of horizontal drainage pipe, expressed in inches of fall per foot of run, that lets gravity move waste and solids toward the sewer. Too little slope causes clogging; too much separates liquids from solids.

The network of roof drains, leaders, area drains, and storm sewers that collects and conveys rainwater and surface runoff away from a building. It must remain separate from sanitary drainage in most jurisdictions.

A fitting installed at a low point of a roof to collect rainwater and direct it into a leader or downspout. Its size and strainer capacity are matched to the roof area and local rainfall intensity.

A two-tier roof drainage design in which the primary system handles normal rainfall and a secondary system, such as scuppers or overflow drains, handles flows exceeding the primary system's capacity to prevent roof collapse.

A tank or vault that slows wastewater so fats, oils, and grease float to the surface and solids settle, preventing grease from clogging sewers. Codes set sizing rules and require periodic pumping and inspection.

A public or private pipe that carries sewage and liquid waste from buildings to a treatment facility. It is kept separate from storm drainage to avoid overwhelming treatment plants during rain events.

The unwanted reversal of water flow in a piping system, which can draw contaminants into the potable supply. It occurs through backpressure, where downstream pressure exceeds supply pressure, or backsiphonage, where supply pressure drops.

Any actual or potential link between the potable water supply and a source of contamination or pollution. Eliminating or protecting cross-connections is the central purpose of backflow prevention programs.

A physical separation between a water supply outlet and the flood-level rim of a fixture or receptacle, providing the highest level of backflow protection. Codes specify a minimum gap, often twice the effective opening diameter.

A testable backflow preventer with two independently acting check valves and a relief valve between them that discharges if either check fails. It protects against both backpressure and backsiphonage in high-hazard applications.

A testable backflow preventer consisting of two check valves in series, used for low-hazard protection where only pollution, not contamination, is possible. It cannot discharge relief flow like an RPZ assembly.

A device that admits air into piping when pressure drops below atmospheric, breaking a siphon before backflow can occur. Hose-bib and flushometer versions are common low-cost fixture-level protections.

The top edge of a fixture or receptacle over which water would overflow onto the floor. It establishes the reference point for air gaps and for setting fixture outlets and backflow devices.

A toilet fixture that receives human waste and discharges it to the drainage system through a trap. Its flush volume, trapway, and fixture-unit rating must meet code and water-efficiency standards.

A flush valve that uses line pressure to deliver a measured flush to a fixture, commonly found on commercial toilets and urinals. It requires adequate flow and pressure and often needs a vacuum breaker.

A pressure surge caused by sudden stopping of water flow, producing banging noises and stressing pipes and fittings. Arrestors, properly sized piping, and slow-closing valves reduce the effect.

A device containing a trapped air chamber or piston that absorbs the pressure spike created when flow stops abruptly. It is installed near quick-closing valves to protect piping and fixtures.

A valve that lowers incoming water pressure to a safe, code-compliant level for downstream fixtures and piping. It protects against excessive pressure that can damage fixtures and cause noise or leaks.

A tank installed on a closed potable water system to absorb the volume increase caused by heating water. Without it, pressure can rise to unsafe levels and cause relief valve discharge or pipe failure.

A safety device on a water heater that opens to discharge water if temperature or pressure exceeds set limits. It must be piped to a safe drain and never plugged or capped.

An appliance that heats potable water for domestic use, available in storage, tankless, and indirect types. Installation requires proper venting, relief protection, seismic or thermal safeguards, and clearance from combustibles.

A piping arrangement that continuously or periodically moves hot water through the system so taps receive hot water quickly. It reduces wait time and water waste but requires balancing and insulation to limit heat loss.

An official authorization issued by the authority having jurisdiction before plumbing work begins, confirming plans and contractor qualifications meet code. Work without a required permit can lead to stop-work orders and penalties.

The organization or official responsible for enforcing the plumbing code and approving installations, materials, and permits. The AHJ interprets code requirements and conducts or authorizes inspections.

A formal review of plumbing work by the AHJ at defined stages, such as rough-in, top-out, and final, to verify code compliance. Approval at each stage is usually required before work is concealed or put into service.

A code inspection performed after piping, fittings, and fixture supports are installed but before walls, floors, or ceilings are closed. It verifies pipe sizing, slope, venting, and test results before concealment.

A pressure test in which a system is filled with water and held at a specified pressure for a set period to reveal leaks. Drainage systems may instead be tested with air or water per code requirements.

A written document that formally modifies the scope, price, or schedule of a construction contract after work has begun. Proper documentation protects the contractor's right to payment for added or changed work.

A record of incomplete or defective items identified near the end of a project that must be corrected before final acceptance and closeout. Clearing it is typically a condition of final payment.

A safety procedure that isolates energy sources and attaches warning tags before servicing equipment, preventing accidental startup or release of stored energy. It is required for work on pumps, heaters, and electrical components.

The controlled process of entering a space with limited access and ventilation that is not designed for occupancy, such as a vault or sewer. It requires atmospheric testing, permits, attendants, and rescue planning.

Gear such as gloves, eye protection, respirators, and hearing protection worn to reduce exposure to workplace hazards. Employers must provide suitable PPE and train workers in its correct use and limitations.