Jargon Buster - H

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Handwheel valve

An isolation valve that has a circular grip for turning by hand.

Hard water

Water that contains concentrates of soluble calcium carbonate greater than 20 parts per million.

Heat emission

Heat energy radiated from any source.

Heat exchanger coil

The device used to transfer heat energy to another medium, such as hot gases in a boiler transferred to the central heating water.

Heat output

The rated output of an appliance, usually given in KW, BTU, or Therms.

Heating flow

The hot water pipe from a boiler to the radiator system.

Heating return

The cooler water pipe returning the water from the radiator system to the boiler for re-heating.

Heating-circuit controller

A specific type of valve used to control the flow of water or steam in a hydronic heating system allowing heat to be directed at specific zones.

Hissing noises

This is caused by overheating due to a variety of reasons, including a blocked chimney, a build-up of scale due to hard water, a faulty boiler thermostat, a lack of water in the system or the pump not working.

Horizontal duct

A service channel that lies parallel with the ground.

Hot water circuit

The water circuit from the boiler to the hot water storage tank.

Hot water cylinder

Hot water passes through the cylinder, heating up the stored water.

Hot water cylinder thermostat

The thermostat controls the temperature of hot water stored in the cylinder. It is usually fitted to the tank with a temperature sensor.

Hot water storage tank

Stores the domestic hot water.

Hot water thermostat

This will be fitted to the side of the hot water tank. It controls the highest temperature of the hot water. Some boiler systems don't need them.


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