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HP – Horsepower

HVAC – Heating, Ventilation, and Air Conditioning

Handles – Faucet handles typically come in 3 styles: knob, lever, and cross. Some manufacturers allow a customer to mix and match components to create a custom handle consisting of handle bases and handle inserts.

Handshower – A showerhead designed with a handle that’s connected to a water supply and a flexible hose.

Hanger – A device used to support pipes.

Hard Water – Natural water containing impurities in various proportions. Traditional hardness is a measure of calcium or dissolved solids in a solution, measured in parts per million. Hard water generally ranges from 100 to 250 ppm.

Hardness – The amount of dissolved minerals in water measured in grains per gallon (GPG). The most common minerals are calcium and magnesium.

Hardness Leakage – The presence of a consistent concentration of hardness in the effluent from an ion exchange water softener, often due to high concentrations of hardness or sodium in the water being treated (see Leakage).

Head / HD – (1) The pressure of water (or steam) in a closed system (see Pressure Head). It represents the differential in the gravitational force exerted by a liquid at two different depths. (2) Nautical slang term for toilet

Head Loss – The pressure of water as measured at a stated point, either in feet or in pounds per square inch (PSI).

Heat Exchanger – A heat transfer system

Heat Sensors – Heat-triggered devices on sprinkler systems that release the flow of water.

Heat Trap – Restriction of heat loss through water connections to a tank.

Hermetic – Completely sealed, especially against the escape or entry of air.

Hex Key – Allen Wrench

Hold Down – A type of pipe anchor consisting of a U-strap bolted at either end onto a horizontal plate.

Hole Saw – A small, cylindrical attachment for a power drill consisting of a circular saw blade for cutting holes.

Hollow-jet Valve – A valve having a closing member that moves upstream to shut off the flow. The hollow-jet valve discharges a hollow or annular jet dispersed over a wide area.

Horizontal Branch – Lateral drain pipes that run from plumbing fixtures to the waste stack in a building or in the soil.

Horizontal Rum – The horizontal distance between the point where fluid enters a pipe and the point at which it leaves.

Hose Bibb – 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.

Hub & Spigot Piping – Gravity rated DWV or pressure pipe that has a bell-shaped section at one end and a straight section at the other. As lengths are assembled, the straight end of one fits into the bell of the next.

Hubless – Same as no-hub. Cast iron drainage pipe with neoprene gaskets and clamps.

Hydraulic Pressure – Pressure that exists in a system containing non-compressible liquid.

Hydrolysis – The reaction of a salt with water to form an acid and a base.

Hydronic – System of forced hot water.

Hydrojet – Cold inlet tube designed to reduce sediment build-up and increase efficiency in a water heater.

Hydro Jetting (Service) – The process of clearing blocked pipes using high pressure water as a boring and flushing mechanism.

Hydrostatic Pressure – Pressure exerted by or existing within a liquid at rest with respect to adjacent bodies.

Hydrostatic Test – Test using non-compressible liquid under pressure at a level equal to or greater than the maximum pressure that will be utilized when in use, such as in steam boilers.

Hydrous – Containing water, water of crystallization or hydration, as certain minerals or chemical compounds.

Hygroscopic – Attracting or absorbing moisture from the air; changed or altered by this absorption.

Hypochlorite – The OCL anion; calcium and sodium hypochlorite are commonly used as bleaches and disinfecting agents.


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Source: “Plumbing Terms” Standard Plumbing Supply. 11 Sept. 2008