Plumbing and Heating Glossary

GlossaryHave you worked with a plumber or heating company that confused you with all the plumbing and heating terms? The following glossary provides definitions of commonly used heating and plumbing words and phrases. At AES Mechanical, we always strive to explain things to you in easy-to-understand terms with a minimum of jargon.


Acrylonitrile-butadiene-styrene. Used for drain and vent lines.

Access Panel

An opening in the wall or ceiling near the fixture that allows access for servicing the plumbing/electrical system.


The system of screens most faucet spouts that help control the flow of water and keep it from splashing. They often contain a baffle to help reduce the flow of water to the mandated 2.5 gallons per minute.

Air Admittance Valve (AAV)

A device that replaces a traditional vent to allow air to enter the pipe and equalize pressure, preserving the seal of water in the fixture trap.


The unobstructed vertical opening in the drainage system between the lowest opening of a waste line and the flood level of the device into which it empties. Its purpose is to prevent backflow contamination.

BTU (British Thermal Unit)

The amount of heat required to raise the temperature of one pound of water, one degree Fahrenheit.

Backflow Preventer

A device that prevents wastewater from flowing into the potable water supply. Generally required for sprinkler systems, hand-held showers installed in bathtubs, faucets with pullout spouts, kitchen sprayers, and the like.


A valve operated by a float, such as a floatball or a float-cup in a toilet tank.


A hot water or steam heating unit. A boiler can be heated with Natural Gas, LP Gas or Oil.


Any part of the drain system other than the main, riser, or stack.


A pipe fitting used to join two pipes of different sizes. A bushing is threaded inside and out.

Check Valve

A type of backflow preventer installed in a pipe run that allows water to flow in only one direction.


A plug in a trap or drain pipe that provides access for clearing clogs and obstructions.

Closet Auger

A flexible rod with a curved end used to access the toilet’s built-in trap and remove clogs.

Closet Bend

The curved section of drain pipe located immediately below the toilet.

Closet Flange

A round, flat fitting that attaches to the closet bend and is used to secure the toilet in place.


A fitting used to join two pieces of pipe.


Chlorinated polyvinyl chloride. Rigid plastic pipe used for water supply systems.


Any connection or situation that may allow waste water to enter the supply system.


Any pipe that carries wastewater or water-borne waste.


Abbreviation for drain, waste, and vent.


Curved fittings, usually 90° or 45°, used to change the direction of a pipe run. Also called “ells.”

Energy Star

A program developed by the Environmental Protection Agency (EPA) to reduce the nation’s energy consumption. ENERGYSTAR® qualified heating equipment can be up to 15 percent more efficient than standard models.

Energy Star Rating

A comparative guide number typically displayed on a new appliance, such as a dishwasher, boiler, or water heater, providing a numerical energy efficiency rating.


A pipe fitting with two openings that changes the direction of the line. Also called an ell. It comes in a variety of angles, such as 45° or 90° bend


The proper slope or pitch of a pipe for adequate drainage.


Any pipe part used to join together two sections of pipe, such as elbows, couplings, bends, wyes, etc.


In plumbing, the devices that provide a supply of water and/ or discharges water or wastewater, such as faucets, sinks, toilets, etc.

Flapper Valve

The part on the bottom of a toilet tank that opens to allow water to flow from the tank to the bowl. When closed, it creates a seal between the two spaces.

Float Ball

In the toilet tank, the hollow ball attached to a rod that rises as the tank refills and shuts the water inlet valve.


The structure through which heated air, or combustion air, moves before they are released from indoors to outdoors.


Substance applied to copper pipes and fittings before soldering to help the fusion process and prevent oxidation.


Device used to support pipes.

Heating Capacity

The rate at which a specific device can add substantial heat to a substance, expressed in BTUh (British Thermal Units per hour).

 Hose Bibb

An outdoor faucet. Also used to supply washing machines.


The Leadership In Energy and Environmental Design (LEED) Green Building Rating System is an independent certification program that provides guidelines for developing energy efficient, sustainable buildings. Certification standards are defined for sustainable site development, water savings, energy efficiency, materials selection, and indoor environmental quality.

LP Conversion

A kit that allows a furnace to be converted to use LP instead of natural gas.


Industry term for bathroom sink.


The primary supply line or drain system to which all the branches connect. Referred to as the main vent in the vent system.


A fitting that connects a number of branches to the main; serves as a distribution point.


A short length of pipe installed between couplings or other fittings.

No-hub Connector

A connector for no-hub iron pipe consisting of a rubber sleeve and a stainless-steel band secured by hose clamps. It is used for connecting dissimilar materials, as when connecting new plastic pipe to an existing cast-iron drain pipe.


The packing material used before sealing a hubbed cast-iron fitting with lead.

PB (Polybutylene)

Flexible plastic tubing used in water supply systems where allowed by code.


Cross-linked polyethylene. PEX tubing, is commonly used for water supply lines and radiant floor heat systems.

Pipe Dope

Slang for pipe-joint compound. The substance applied to threaded fittings to create a watertight seal.

Plumbers Putty

A pliable putty used to seal joints between drain pieces and fixture surfaces.


Water that is suitable for consumption.

Pressure-balancing Valve

A mixing valve that monitors the water pressure in both the hot and cold supply lines and compensates for a drop in either one.

PVC (Polyvinyl Chloride)

A rigid white or cream colored plastic pipe used in non pressure systems, such as waste and vent systems.

Radiant Floor Heating

Radiant heating systems circulate warm water through tubing embedded in the floor to warm the people, furnishings, and air in a room.


A fitting that allows pipes of different sizes to be joined together.

Relief Valve

A valve that opens to relieve excess temperature or pressure in the system.


A supply line pipe that rises from one story to the next. It also refers to the short vertical pipes that bring water from the branch to a fixture.


The portion of a plumbing installation that includes running the water supply lines and drain, waste & vent lines in the structure (walls, floors, etc.) prior to installation of fixtures such as sinks, faucets, and toilets.


A complete or secondary section(s) of pipe that extend from supply to fixture or drain to stack.

Setback Thermostat

An electronic thermostat with a built-in memory that can be programmed for different temperature settings at different times of the day.

Shutoff Valve

Most commonly refers to the shut-off valve located under sinks and toilets. Valves are also installed on branch lines and alongside the meter.


Another name for hose bibb.

Soil Stack

The largest vertical drain line to which all branch waste lines are connected. It carries waste to the sewer line.


A metal alloy that is melted to create a fused joint between metal pieces.

 Stop Valve

A valve that controls the flow of water to an individual fixture, allowing water supply to be stopped to one fixture without affecting the water supply to other fixtures.


Short lengths of pipe installed during rough-in to which fixtures and drains will eventually be installed.


Slang for soldering.


The eased change of direction in a drain fitting that allows for smooth passage of waste. Fittings with abrupt changes of direction, such as a vent tee, may only be used for vents.

T&P Valve

Temperature and pressure valve. A valve that opens to release excess pressure and temperature in a system.


The section of pipe that runs between a fixture outlet and the trap.

Tee Fitting

Fittings that allow pipes to be joined at a 90-degree angle. Tee-fittings for drain systems use a sweeping bend to prevent blockage. See Sweep.


A temperature control device, typically located on an inside wall that is used to set and maintain a desired room temperature


A fitting or portion of a fixture that, when properly vented, holds water to prevent entry of sewer gases.


A device that regulates the flow of water.

Valve Seat

The immovable portion of a valve. Water flow is stopped when the movable portion of the valve comes in contact with the valve seat.

Vent Stack

The upper portion of the soil stack above the topmost fixture through which gases and odors escape.

 Water Hammer Arrestor

A device installed near a fixture to absorb the hydraulic shock that happens when a fixture’s supply is suddenly shut off, causing water hammer, a loud banging noise in the pipes.

Wye Fitting

A Y-shaped fitting with three openings used to create branch lines.

Zoned Heating System

A method of partitioning a home into independently controlled comfort zones for enhanced comfort and efficiency. Zone Control Systems eliminate “hot and cold spots” and can help save energy.

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