A Glossary of Radiator Terms

Air vent – A small valve, which enables air that has accumulated at the top of a radiator to be let out or ‘bled’ from the radiator using a special air vent key. Also known as a bleed valve or bleed vent.

Angled valves – Valves that have a 90 turn on them for use on radiators with side valve connections, where pipe work is coming up from the floor or out of the wall. Also used on radiators with underside valve connections, but only where the pipe work comes out of the wall. See also “Straight valves.”

Balancing – Adjusting the flow of water throughout a piped central heating system in order to achieve a similar drop in temperatures across all radiators. It is important to ensure that heat is distributed evenly to all radiators so that they all run at equal temperatures and all take an equal amount of time to reach their operating temperature. A plumber should ‘balance’ the system after installing radiators. Lack of balancing within a system is often the cause of cold spots on radiators, radiators failing to heat up properly or noisy radiators.

BBOE – Bottom Bottom Opposite Ends – Radiator valves are installed at the bottom of the radiator, on either side.

Bleeding a radiator – Getting rid of any air that has accumulated at the top of radiator, using an air vent or bleed valve. Trapped air in a radiator will result in a radiator failing to heat up properly.

Bleed valve – see “Air vent”

Bleed vent – see “Air vent”

Boiler – a device that heats water using gas, oil or electricity. This is the most common way to provide hot water central heating for domestic properties.

Bracket – a part used to secure/fix radiators to the wall

British Thermal Unit – (BTU or Btu) is a traditional unit of energy equal to about 1,055 joules. It is approximately the amount of energy needed to heat 1 pound (0.454 kg) of water (therefore around 0.1198 gallons) from 39 to 40 F (3.8 to 4.4 C). This unit of measurement is now being replaced with the alternative unit of measuring heat output, Watts.

BS 3528 – The old British standard for radiators. BS EN 442 has now superseded this.

BS 5449: 1990 – The British Standard for internal room temperatures, identifying acceptable comfort levels.

BS 7593: 2006 – The British Standard for the treatment of water in domestic hot water central heating systems, including the use of corrosion inhibitors and cleaners.

BS EN 12828 & 12831: 2003 – British Standards for designing heating systems.

BS EN 442 – The official European Standard for radiators. It covers various standards that radiators need to meet including heat output, minimum material thickness, pressure tests, paint quality, product labelling, safety, etc.

BTU – See “British Thermal Unit”

Bush – see “Reducer”

Central Heating – A system that provides warmth to the whole interior of a building (or portion of a building) from one point to multiple rooms.

Closed System – A piped central heating system that is “closed” or “sealed” means that the water contained within the system is taken from the water mains upon installation. Once filled and pressurised the system is sealed off and then the water within the system is circulated repeatedly around the system and is not (unless actioned via the filling loop) replaced by new water entering the system.

Combi boiler – a device that provides both central heating and hot water. A combi boiler is a high-efficiency water heater and a central heating boiler, combined (hence the name) within one compact unit. Therefore, no separate hot water cylinder is required, offering space saving within a property. “Combis” are a very popular choice for domestic properties. copper radiator

Combination boiler – see “Combi boiler”

Convector – a device that is designed to “convect” heat, using the physics of warm air rising and cold air falling to create a natural cycle of air circulating around a room. Radiators convect heat as well as radiating heat.

Corrosion inhibitor – a chemical that installers add to the water in standard piped central heating systems to prevent internal corrosion of non-inert metals as per BS 7593: 2006. Examples of corrosion inhibitors include Fernox MB-1 and Sentinel X100.

Direct System – Cold water is taken from the mains and goes directly to points of delivery (taps) around a property where cold water is required.

Dt – Also written as Dt or Delta t. “BTUs” or “Watts” are a measure of how good a radiator is at heating a room at standard temperature; the Dt value defines what that standard temperature is. Naturally the hotter a radiator is, the more heat it gives out. Since water cools on its passage through a radiator, the temperature of the water entering it is higher than the temperature of the water leaving it. The mean value of the inlet (flow) and outlet (return) temperatures is taken and the approximate room temperature is subtracted from this figure, universally quoted as 20C. The difference, known as Dt, is the operating temperature that is given in the radiator’s specifications.

Dt of 50C – Delta t 50: The European standard for the operating temperature of central heating systems, which determines the heat outputs achievable from radiators.

Dt of 60C – Delta t 60: The British standard for the operating temperature of central heating systems, which determines the heat outputs achievable from radiators.

Duel Fuel – A radiator that is connected to the central heating system, but also has an electric element for use in the warmer months when the central heating isn’t turned on. A popular choice for bathroom radiators.


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