Glossary of Basic Plumbing Terms: Heating

by Chelsea Oliver 8th March 2017

yabsta great britain glossary of heating terms

Air Handling Unit (AHU)


A unit that includes a blower or fan that provides heat, ventilation and air conditioning (HVAC) to a building.  


Air Source Heat Pump (ASHP)


A heat pump that absorbs heat from outside air, transferring it to the space to be heated. In cooling, an ASHP absorbs heat from the space to be cooled, rejecting the heat to the outside air.


Back Boiler


A boiler fitted behind a real fireplace. Used with a direct cylinder, a back boiler heats the room it’s in and also provides hot water for central heating and use in the household. These models are rarely installed today, having been more common in the 1970s and 1980s.


Baseboard Radiator


A radiator that fits along an exterior wall where that wall meets the floor.




A measurement of atmospheric pressure that is equal to the pressure felt at sea level on earth. BAR has replaced the older unit of ‘one atmosphere’, which is equivalent to 1.013 BAR.


Bleed Valve


Typically situated at the top of a heated towel rail or radiator, a bleed valve is used to expel air, increasing appliance efficiency.




A hot water tank that heats water, turning it into steam before distributing it through a home or building via pipework. It is often a power source for hot water systems, radiators and heated towel rails.


Boiler Pressure


Measured in BAR, the pressure of the steam or water inside a boiler and heating system at any time. To find out what the pressure is set at, check the gauge, which is typically situated on or below the boiler.


Central Heating


The most common form of heating in the United Kingdom, a central heating system uses a single boiler. The boiler heats water which is then pumped through pipes to radiators distributed throughout the house. Hot water is also provided to the bathroom and kitchen.


Combi Boiler


A boiler that heats water straight from the mains, providing an unlimited supply of hot water. Combi boilers do not require a hot water cylinder or cold water storage tank.


Combined Heat and Power (CHP) Unit


A CHP unit efficiently generates both electric and heat energy. It’s comprised of an engine, a synchronous generator and a heat exchanger, and is typically installed within a light commercial setting, public building or as part of a district heating system. CHP units generate both power and heat (or mechanical and thermal energy).


Condensing Boiler


A boiler that uses heat from exhaust gases. The water vapour from the exhaust gas turns into liquid condensate and, in order to make use of the latent heat, these boilers use a large heat exchanger and, in some cases, a secondary heat exchanger. A condensing boiler extracts more heat from its fuel than a standard boiler.


Convection Wall-Mounted Gas Heater


A heating unit that is mounted to the wall, using a flame to heat the air and a fan to circulate the warmed air.



The movement caused within a fluid (such as water or air) by the tendency of hotter, less dense material to rise, and colder, denser material to sink under the influence of gravity. This results in the transfer of heat.


Convector Radiator


A radiator that transfers heat via convection. Convector radiators typically have ‘fins’ at the back or in between the panels, increasing surface area and, in turn, increasing the amount of heat emitted.


Direct Hot Water Cylinder


A water cylinder that is most often heated by an immersion heater or other internal element. It is aptly named as the immersion heater heats the water in the cylinder directly. It is Electric Only, as the water in the cylinder is not heated by any other source such as a boiler. Hot water is fed out of the top of the cylinder to, for example, taps and baths. Available in vented and unvented models, direct cylinders are typically used in situations where there is no central heating.


Drain Down


The process of removing all of the water from a central heating system.


Dual Fuel Radiator


Operates like a typical radiator when the central heating system is turned on. When the central heating system is turned off, a dual fuel radiator can run on electricity.




A home or building’s air distribution system for heating and air conditioning.


Electrical Heating Element


Inserted into an electric or dual fuel radiator, an electrical heating element allows the appliance to operate independently of the central heating system.


Electric Heating


U.K. homes without a boiler and radiators are warmed by electric storage heaters. Electric storage heaters heat up overnight when electricity is less expensive and then give out heat during the day. They typically require a hot water cylinder as well as at least one immersion heater. Electric heating is most common in rental properties, flats and homes that do not have a main gas connection, and is one of the more expensive options.


Electric Radiator


A radiator that is plugged into the wall and runs on electricity. Electric radiators are energy efficient and allow for managing heat inside a home or building on a room-by-room basis.


Electric Water Heater


An electricity powered water heater that can be connected to the mains water supply and stored on the counter, under the sink or mounted to the wall. A wide range of models are available.




A heating unit that uses oil or natural gas to heat a building. Furnaces are typically located indoors.


Gas Central Heating


A system wherein a gas-fired boiler heats water to provide both central heating via radiators and hot water. Mains gas central heating is common in most U.K. households.


Heat Exchanger


The part of the furnace that transfers heat into the air inside the unit. The hot air then travels throughout the building via the ductwork.


Heated Towel Rail


A multi-purpose appliance that is both towel rail and radiator. It heats the bathroom while both warming and drying towels. A wide choice of models are available in a range of materials and finishes.


Hot Water Cylinder


A container commonly used for for storing large amounts of hot water, which is available on demand for use in the kitchen, bathroom and throughout the home.


Hybrid Appliance


An appliance supplied by a range of energy sources. For example, a dual mode heat pump system, which features a fossil fuel boiler as well as an electric heat pump.




Heating, Ventilation and Air Conditioning (HVAC).


Immersion Heater


An electric water heater that sits inside of a hot water cylinder. Connected to its own power supply, an immersion heater is often used as a backup for a combi boiler.  


Indirect Hot Water Cylinder


A cylinder that is heated via an external heat source, such as a boiler. A heat exchanger or internal coil heats the water inside the cylinder, transferring heat obtained from an external source. An indirect hot water cylinder often includes an immersion heater, a supplementary heat source that allows the water to be heated when the boiler is turned off. Indirect cylinders heat up and recover faster than direct cylinders, and both vented and unvented models are available.


Liquefied Petroleum Gas (LPG)


A mixture of gaseous hydrocarbons that are produced from natural gas, oil extraction and the refinery of that oil. An associated gas, it is generated automatically during the production of methane in the refining process.


Liquefied Petroleum Gas (LPG) Central Heating


A system wherein an LPG-fired boiler heats water that is then supplied to both radiators and taps within a home. LPG Central Heating differs from Gas Central Heating in that LPG is delivered and then stored inside a tank.


Low Water Content Boiler


Contains only a small amount of water for fast and efficient heating.


Natural Gas


A light hydrocarbon fuel found naturally where oil and coal have formed. Natural gas contains methane, ethane, butane, propane and nitrogen.


Oil Central Heating


A system wherein an oil-fired boiler provides hot water for central heating via radiators and taps in the home. Like LPG, heating oil is delivered and stored inside of a tank.


Open Vented Hot Water Cylinder


Also called a cistern fed cylinder, an open vented cylinder has a header tank in the loft area that feeds through cold water from the mains feed. It relies on gravity to push the water through the pipes to the heating or hot water system. Typically made of copper, open vented cylinders are associated with regular, heat only boilers and conventional heating systems.


Pellet Stove


A space heating device that burns pellets.


Portable Electric Heater


A small, portable appliance that generates heat via electricity. A portable electric heater is most often used for heating a small area.


Portable Gas Heater


A small, portable appliance that burns propane, liquefied petroleum gas, natural gas or butane to generate heat for a small area outdoors or indoors. For indoor models, both flued and non-flued, and vented and unvented are available.


Pressure Relief Valve


A valve that allows excess water pressure to safely drain. This prevents over-pressurisation.


Radiant Heat Wall-Mounted Gas Heater


A gas heater that is mounted on the wall wherein a flame heats a ceramic element, providing radiant heat for both people and objects in the area.




A device that sends out heat, often as part of a heating or cooling system.


Regular (Conventional) Boiler


A regular (or conventional) boiler sends hot water to a radiator and a hot water cylinder. Water goes to multiple taps at once in the home.

Secondary Heating


When a household or building uses an individual heater, such as a portable gas or electric heater, range cooker or traditional gas fire, in addition to central heating.


Solar Hot Water Cylinder


Designed for solar heating installations, a solar cylinder utilizes a mixture of Glycol liquid, which absorbs the maximum heat from the sun’s rays, and water. This mixture is circulated through pipe work in the solar panels and then returned to the cylinder, transferring the heat to the stored water via a heat exchanged. The liquid is then pumped back to the solar panels, where it is reheated.


Solar Hot Water System


A system that captures the energy radiated by the sun within solar collectors or panels, harnessing the sun’s heat. Solar hot water systems reduce carbon footprint and lower energy costs by reducing reliance on electricity, gas and oil for hot water.


Solid Fuel


All fuels that are available in a solid state (ex: wood, peat, charcoal, pellets, coal).


Regular (Conventional) Boiler


A regular, or conventional, boiler, delivers hot water to both a radiator and a hot water cylinder. Water is sent to taps simultaneously, which is ideal for homes with more than one bathroom.


System Boiler


A boiler that pumps hot water through a central heating system directly to the radiators and hot water cylinder. It contains an expansion vessel and pressure relief valve.


Tankless (Instant) Water Heater


A tankless (or instant) water heater heats water as it flows through the system and does not require a tank of water to be kept at a proper temperature in order to work. It provides instant hot and cold water and operation is economical. Under sink, over sink, vented and unvented models are available.


Thermal Store Hot Water Cylinder

A cylinder wherein the water held inside is heated via an internal or external heat source. Cold water is then pumped through the cylinder and, while it passes through the heated cylinder, the temperature of the water raises. The cold water then exits the thermal store cylinder as hot water. This is the opposite of how a standard hot water cylinder functions. Thermal store cylinders do not require pressure and temperature relief valves and can accept input from a range of energy sources.




A device that automatically regulates temperature, or activates a device when the temperature reaches a certain point.


Thermostatic Radiator Valve


A valve that is fitted to a radiator and used to control room temperature. Thermostatic radiator valves limit the temperature within each room, reducing the energy used by heating systems.


Three-Pass Boiler


A boiler wherein hot gases flow through the combustion chamber and then returns to the front via a reversing zone, entering a third pass. The combustion gases spend less time in the hottest part of the boiler, reducing harmful emissions.


Under Floor Heating


A form of central heating that utilizes conduction, radiation and convection to achieve indoor climate control. Both electric and water under floor heating is available.


Unvented Hot Water Cylinder


A cylinder that works off of the mains pressure water, eliminating the need for a header tank in the loft. Unvented cylinders work with system boilers and offer stronger water pressure. A feeder tank is not required, which is great for saving space.


Water Heater


An appliance comprising an electric or gas heating unit underneath a tank wherein water is heated and stored.


Water Source Heat Pump (WSHP)


A heat pump that uses water from the ground, or surface, as a source of heat. A WSHP is highly efficient.


Wood Stove


A wood burning appliance typically used to heat a water tank or space in a home or building. Wood stoves can also be used for cooking.



An area within a building’s interior that is to be heated, cooled or ventilated.

Posted by ChelseO
8th March 2017 12:00 am.
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