Plumbing Contractors Industry Terminology

AAV (Air Admittance Valve)

A one-way, mechanical vent that admits air into a DWV system to prevent trap siphonage when a roof vent is impractical. Not accepted by all codes or in all locations.

ABS (Acrylonitrile Butadiene Styrene)

A rigid black plastic commonly used for drain, waste, and vent piping. Known for impact resistance and ease of solvent welding; typically for DWV, not for hot potable water.

ADA Compliance

Conformance with the Americans with Disabilities Act requirements for accessible plumbing fixtures and spaces, including mounting heights, clear floor area, reach ranges, and knee/toe clearance.

As-Built Drawings

Record documents that reflect the actual installed conditions after field changes, used for operations, maintenance, and future renovations.

Backflow

Unwanted reversal of water flow that can introduce contaminants into the potable system via backsiphonage or backpressure. Requires approved backflow prevention assemblies.

Ball Valve

A quarter-turn isolation valve using a bored sphere to start/stop flow; favored for low pressure drop and reliability.

Bid Bond

A surety bond guaranteeing the bidder will honor their bid and provide performance and payment bonds if awarded the contract.

BIM (Building Information Modeling)

A digital 3D model process used to coordinate MEP systems, detect clashes, produce prefabrication spools, and streamline installation and documentation.

Change Order

A formal modification to the contract scope, price, and/or schedule, typically initiated by owner directives, unforeseen conditions, or design changes.

Code Compliance

Adhering to applicable plumbing codes (e.g., UPC, IPC) and local amendments covering design, materials, installation, testing, and inspection requirements.

Cleanout

An access point in the DWV system that allows mechanical cleaning and inspection of piping.

CPVC (Chlorinated Polyvinyl Chloride)

A thermoplastic piping material suitable for hot and cold potable water, offering better temperature resistance than standard PVC.

Cross-Connection

Any physical connection between potable water and a non-potable source that could permit contamination. Must be protected with approved devices.

Dielectric Union

A fitting that electrically isolates dissimilar metals to mitigate galvanic corrosion at pipe transitions.

Double-Check Valve Assembly (DCVA)

A backflow prevention assembly with two check valves in series, used to prevent backflow in low-to-moderate hazard situations.

DWV (Drain-Waste-Vent)

The plumbing system that removes wastewater and vents sewer gases, requiring proper slopes, traps, and venting to function correctly.

Estimator

A professional who quantifies materials and labor, analyzes risk, and prepares cost proposals for plumbing projects.

Expansion Tank

A pressurized tank that absorbs thermal expansion in closed water systems to prevent overpressure, nuisance relief valve discharge, and component damage.

Fixture Unit (FU)

A standardized measure of probable demand from fixtures used for sizing water supply and drainage piping.

Flange

A projecting rim or collar used to connect piping to equipment or fixtures with bolts or clamps; includes specialized types like closet flanges.

Flux

A chemical agent applied to metal surfaces to remove oxides and promote wetting during soldering of copper tubing.

Gallons per Minute (GPM)

A flow rate unit indicating the volume of liquid passing a point each minute, used for sizing and performance verification.

Grease Interceptor

A device that captures fats, oils, and grease from kitchen wastewater before it enters the sanitary sewer, preventing blockages.

Greywater

Lightly used wastewater from sinks, showers, and laundry (not including toilet waste), sometimes reused for irrigation or flushing under local regulations.

Hangers and Supports

Hardware and assemblies that support and secure piping to the structure, designed per load, spacing, vibration, and seismic requirements.

Hydronic Heating

A heating system that circulates hot water through piping to terminal units or radiant slabs for space heating.

IAPMO Listing

Product certification by the International Association of Plumbing and Mechanical Officials indicating compliance with applicable standards and codes.

IPC (International Plumbing Code)

A model plumbing code published by the ICC that sets minimum requirements for plumbing systems; many jurisdictions adopt it, sometimes with amendments.

IPS (Iron Pipe Size)

A legacy pipe sizing system that defines nominal pipe sizes and matching thread dimensions; still used for steel pipe and threaded fittings.

Isolation Valve

A valve installed to shut off flow to a portion of the system for maintenance or emergencies without affecting the entire system.

Journeyman Plumber

A licensed tradesperson who has completed apprenticeship and is qualified to install and service plumbing systems, often supervising apprentices.

Lead-Free

A regulatory requirement limiting the weighted average lead content of wetted surfaces in potable water products to 0.25% (per federal law and NSF/ANSI 372).

Lien Waiver

A document waiving the right to place a mechanic’s lien for labor or materials once payment is received, used to protect owners and GCs.

Lift Station

A pumping system that moves wastewater from lower to higher elevation when gravity flow is not possible.

Manifold

A distribution header that divides flow into multiple branches, common in PEX domestic systems and hydronic loops.

MEP Coordination

The process of aligning mechanical, electrical, and plumbing system layouts to avoid clashes and ensure maintainable, code-compliant installations.

Method of Procedure (MOP)

A step-by-step plan for executing critical work such as tie-ins, shutdowns, and cutovers, minimizing risk to building operations.

No-Hub Coupling

A rubber sleeve with a stainless steel shield and clamps used to join cast iron soil pipe and fittings without hubs; also used for approved transitions.

NPT (National Pipe Taper Thread)

A U.S. standard tapered thread for pipe and fittings that seals via thread interference; common on steel, brass, and some plastic components.

O&M Manuals

Operations and maintenance documentation provided at closeout, including product data, maintenance instructions, warranties, and parts lists.

OS&Y Valve

Outside Screw and Yoke gate valve with a rising stem that shows valve position; commonly used on fire protection and main shutoff applications.

PEX (Cross-Linked Polyethylene)

A flexible plastic tubing for hot and cold potable water; types A, B, and C differ in manufacturing and fitting compatibility.

P-Trap

A U-shaped trap that retains water to seal sewer gases from entering occupied spaces; must be properly vented to prevent siphonage.

PRV (Pressure Reducing Valve)

A control valve that reduces high inlet pressure to a lower, stable downstream pressure to protect fixtures and piping.

PVC (Polyvinyl Chloride)

A white or gray thermoplastic used for DWV and cold-water applications; joined by solvent welding; not typically used for hot potable water.

Punch List

A checklist of incomplete or deficient work items identified near project completion that must be resolved before final acceptance.

RFI (Request for Information)

A formal question to the design team seeking clarification of plans, specifications, or site conditions to avoid misinterpretation and rework.

Rough-In

The phase of installation when piping, valves, and vents are installed within walls, ceilings, and floors before finishes are applied.

Scope of Work (SOW)

A detailed description of the tasks, deliverables, boundaries, and responsibilities for a project or trade package.

Submittals

Product data, shop drawings, samples, and certifications submitted for design team review to confirm compliance before procurement and installation.