HVAC and Plumbing Terms

The plumbing and HVAC industries have an overwhelming amount of industry terms and acronyms. We’ve put together this list of common terminology to help our customers understand better what is being prepared, what needs to be purchased and what makes it all work.

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AC (Alternating Current): A type of current where the polarity is perpetually reversing, causing the directional flow in a circuit to reverse at regular intervals.

Aerator: A device attached to the end of a faucet that mixes air into flowing water.

Air-Gas Ratio: Ratio of combustion air supply flow rate to the fuel gas supply flow rate.

Air Handler: Indoor part of the air conditioning system including the circulating fan and evaporator (summer)/condenser (winter) coil.

Alarm Check Valve: A check valve located in the riser of a wet pipe fire sprinkler system that sounds an alarm when water begins to pass through it.


Ball Check Valve: A valve that uses a ball to seal against a seat to stop flow in one direction.

Bleed: The process of draining a pipe of excess air by opening a valve at the end of the pipe.

BTU: Stands for British Thermal Unit and it is a measurement of the amount of heat required to raise or lower the temperature of one pound of water one degree Fahrenheit.

Burner: The device that facilitates the combustion of air and gas.


Centrifugal Pump: A pump that moves water by centrifugal force developed by rapid rotation of an impeller. As the rotating impeller whirls the water, centrifugal force builds up pressure forcing the water through the discharge outlet.

CFM (Cubic Feet per Minute): A measurement of airflow volume.

Cleanout Plug: A plug in a trap or drain pipe that provides access for the purpose of clearing an obstruction.

Compressor: A pump that increases the pressure of refrigerant gas.

Condenser Coil: Generally the outdoor coil, it removes the heat from the refrigerant in the summer months, allowing the refrigerant to be converted from vapor to liquid and complete the refrigeration process.


Degree-Day: Calculated by subtracting the average outdoor temperature for an area from 65 degrees Fahrenheit. This measurement is used to determine an estimate for the amount of heating or cooling a residence or building will require.

Drain Pan: Also called a condensate pan. As refrigerant vapor turns to liquid, the drain pan collects the condensate and funnels it to the drain line.

Drip Channel: A metal channel that is designed to prevent water running down a shower door from dripping onto the floor when the door is opened.

Duct work: A network of metal, fiberboard or flexible material flowing throughout a space which delivers air from an HVAC unit to the respective areas of a home or office.


Electrolyte: A non-metallic substance that carries an electric current, or a substance which, when dissolved in water, separates into ions which can carry an electric current.

EPA: The United States Environmental Protection Agency. Created for the purpose of protecting human health and the environment by writing and enforcing regulations based on laws passed by Congress.

Evaporator Coil: A device that is designed to absorb heat in the air in order to change the liquid refrigerant that flows through it into a vapor initiating the cooling process.

Expansion Tank: A tank designed to absorb excess pressure due to thermal expansion.


Feed Pump: A pump that supplies water to a boiler.

Flapper Valve: The part on the bottom of the toilet tank that opens to allow water to flow from the tank into the bowl.

Flue: A vent that removes the byproducts of combustion from a furnace.

Furnace: The major gas-fired component in for heating a home. A device that facilitates the combustion of fuel and air to create heat and then circulates it through the home by means of a fan.


GPM (Gallons Per Minute): A measure of the rate at which water flows through a fixture or fitting at a certain pressure. It is measured by the number of gallons flowing from the device in one minute at a given water supply pressure.

GFCI (Ground Fault Circuit Interrupter): A device to cut off the flow of electricity if a short circuit is detected.


Heat Loss: The amount of heat lost or subtracted from a designated area.

Heat Pump: A device used for heating or cooling an area by transferring heat between two reservoirs.

Heat Transfer: The flow of heat from one area to another by conduction, convection and/or radiation. Heat flows naturally from a warmer to cooler material or space.

Hose Bib: An outdoor faucet, also used to supply washing machines.

House Trap: U-shaped fitting with two adjacent cleanout plugs visible at floor level if main drain runs under floor.


Ignition: Elevating the temperature of a substance to the point of causing a combustive reaction.

Interceptor: Device for separating grease and oil from drainage system.


Jacket: The heating/cooling jacket surrounding the stuffing box on some pumps. The outer casing of a water heater.

Joint: One length of pipe.


Kollar Kap: Styrofoam forms used to protect floor drains while concrete is being poured around them.


Leach: In the case of plumbing systems, leaching refers to the process of dissolving a soluble component out of a constituent material at a wetted surface. Materials commonly leached into drinking water from water distribution systems include copper, lead and nickel.

Leader Pipe: A pipe that carries rainwater to the ground or sewer.

Lock Nut: Nut fitted into a piece of pipe and screwed into another pipe to join both pieces of pipe.


Manufacturer Approved System: If replacing a condensing unit, furnace or air handler, the system must be manufacturer-approved and Air Conditioning, Heating and Refrigeration Institute (AHRI) matched.

Metal Fatigue: A breakage of the metal caused by the bending and flexing or the expansion and contraction of a metal part beyond its endurance limit.


Non-Potable: Water not suitable for drinking.


Outlet Sewer: Pipe section in a septic system which runs between the septic tank and the drainage field.


Plenum: A pressurized housing containing a gas (usually air) at positive pressure (pressure higher than surroundings). Plenum is used to manage and equalize pressure for more even distribution.

Pre-Charged Tank: A water storage tank pre-charged with air at factory featuring a vinyl bag to separate water from air which prevents water logging. This tank design provides greater draw-down than standard tanks. Pre-charged tanks do not require air volume control.

PVC: Polyvinyl chloride; A type of plastic used for pipe.



Radiant Floor: A type of radiant heating system where the building floor contains channels or tubes through which hot fluids such as air or water are circulated.

Refrigerant Charge: The amount of refrigerant in a system.

Relief Valve: A valve that opens to relieve excess temperature.

Return Circulation System: Tempered water from or near the point of usage which eliminates waste of hot water used for long runs and adds storage to the system.


SEER: The efficiency of air conditioners is often rated by the Seasonal Energy Efficiency Ratio which is defined by the Air Conditioning, Heating and Refrigeration Institute as the cooling output during a typical cooling season divided by the total electric energy input during the same period.

Slip Joint: A connection made with compression fittings.

Split System: An outdoor unit combined with an indoor unit, generally providing more efficiency and configuration options.


Thermostat: A wall mounted device that monitor and controls the output of an HVAC system.

Trap: Curved section of drain line that prevents sewer odors from escaping into the atmosphere. All fixtures that have drains must have a “P” trap installed. A toilet is the only fixture that has an “S” trap.


Ultra Low Flow: Refers to plumbing fixtures and fittings that exceed the water efficiency standard of the Energy Policy Act of 1992.

Union: Three-piece fitting that joins two sections of pipe, but allows them to be disconnected without cutting the pipe. Used primarily with steel pipe; never in a DWV system.

Upflow Furnace: A furnace that pulls in air from the bottom and releases it through the top.


Valve: A fitting with a movable part that opens or closes one or more passages and allows a liquid flow to be started, stopped and regulated. In plumbing, valves are used in faucets and showers and can be called mixing valves because they control the mix of hot and cold water to achieve desirable water temperature.

Valve Seat: The non-moving part of a valve. Water flow is stopped when the movable portion of the valve comes in contact with the valve seat.

Ventilation: The process of moving air (changing) into and out of an interior space either by mechanically induced means.


Wet Bulb Thermometer: A thermometer that measures the relative humidity in the air.

Working Pressure: Maximum pressure of the operating system permissible.

A Y-shaped fitting with three openings used to create branch lines. Allows one pipe to be joined to another at a 45-degree angle.



Yoke Vent: A pipe connecting upward from a soil or waste stack to a vent stack for the purpose of preventing pressure changes in the stacks.


Zoning: A system that divides a home, office or space into different regions in order to better control the temperature and effectiveness of a heating and cooling system.

McAtee Plumbing, Heating and Cooling provides reliable service to six different states. Contact us today if you need help with a leak.

For Clarksburg, Fairmont, Morgantown, Weston, Charleston, Huntington and surrounding areas in West Virginia, call 304-623-3102. For Charleston and surrounding areas in Ohio, call 614-252-9400. For Detroit and surrounding areas in Michigan, call 313-277-9969. For Atlanta and surrounding areas in Georgia, call 678-367-0116. For Columbia, Charleston and surrounding areas in South Carolina as well as the Charlotte area of North Carolina, call 843-352-3116. Or you can contact McAtee by email at service@mcateellc.com Visit our website at www.mcateellc.com