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This glossary contains explanations of the main heating jargon terms. You can use it to quickly and easily find the meaning of terminology used in a price quote or a catalogue. 

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Also known as a circulation pump or circulator, the accelerator circulates the heating water between the boiler and the rooms that need to be heated. Very old installations do not have accelerators; they function using the thermosiphon process.

Accumulation or semi-accumulation
A domestic hot water reserve is heated in advance and stored in a tank or an accumulation tank. This process is essential where hot water is required in significant quantities, with a constant temperature.

Ambient thermostat
This complements the action of the boiler thermostat, by measuring the temperature of the room in which it is located. When the room temperature reaches the preset temperature on the ambient thermostat, the boiler thermostat shuts down the burner or the accelerator.

 Atmospheric burner
Atmostpheric burner boilers account for almost all domestic floor-standing gas boilers. The flow of the pressurised gas draws in all or part of the air necessary for combustion. In atmospheric burners with "total premixing", all the primary air is premixed with the gas inside the burner. The mix is very uniform and produces an excellent level of combustion cleanliness, with excellent efficiency and low polluting emissions. 

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Bleed device
An expansion vessel installation has a separate vessel to collect excess water that is created during heating. This vessel must have at least one bleed device, generally positioned at the highest point of the installation, which is used for releasing the displaced air from the vessel. The bleed device can be manual or automatic.

Boiler tank
With a capacity ranging from 50 to 250 litres, the boiler tank can be "incorporated", or "juxtaposed", to the boiler. It is "incorporated" when it is housed in the same casing as the boiler’s body. It is "juxtaposed" when, built separately, it is positioned beside the boiler.

Boiler thermostat (or aquastat)
This device is used to control the boiler to meet heating requirements. This can consist of a simple thermostat positioned on the boiler or an ambient thermostat which also measures the temperature of the room. Modern installations, however, increasingly rely on automatic or even programmable control systems.

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Condensing boiler
Smoke has a high steam content. In a condensing boiler, the smoke is cooled by the return of heating water. The steam condenses and its latent condensation heat is transferred to the return water, adding to the combustion heat. With this process, we can reach an efficiency level (NCV) above 100 % and can make significant energy savings.

Control system
A control system is used to control the boiler for the following functions : regulation of the boiler’s temperature taking into account outdoor temperatures and weekly programming with three operating modes (automatic, permanent comfort, holiday period). The DIEMATIC Delta’s programmable control system is highly evolved, easy to use and can be controlled remotely.

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Domestic hot water priority
Domestic hot water boilers are generally fitted with a domestic hot water (d.h.w.) priority device. Upon request from the d.h.w. sensor, the priority device shuts down the heating pump and starts up the d.h.w. load pump. All the boiler’s power is directed towards the d.h.w. tank for fast refilling. The tank’s capacity must correspond to the power of the boiler. For a domestic boiler (from 18 to 40 kW), a 130 to 150 litre tank provides an excellent level of comfort.

Dual function boiler
The dual function boiler (or mixed boiler) integrates an instant domestic hot water production process. This is suitable for 1-room or 2-room apartments, with a maximum of three water supply points (kitchen sink, washbasin, shower).

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The efficiency is the ratio between the energy consumed (power input) and the energy available for heating (useful output). 100 % efficiency means that 100 % of the power input is returned in the form of heat. A boiler’s efficiency depends on a number of factors : the quality of materials used for the boiler’s heating body, the design of the burner, and the control system. Modern boilers have high efficiency rates ranging from 92 % to 95 %; these rates exceed 100 % with condensing boilers.

Eutectic cast iron
A eutectic heating body is made of cast iron, produced using De Dietrich’s technological expertise. The technology enables the boiler to durably withstand variations in temperature, and corrosion. The eutectic cast iron’s components (iron, carbon, silicon, etc.) are measured in very precise proportions to obtain their fusion at a very constant temperature. The cast iron produced using this process is as an excellent uniformity, with no inherent weak points. This results in an excellent resistance to corrosion.

Expansion vessel
Water expands when it is heated. A vessel capable of absorbing the expansion therefore needs to be positioned on the circuit. In installations fitted with an accelerator, the expansion vessel is "closed" and contains air or a gas which is separated from the water by a membrane. In thermosiphon installations, the expansion vessel is positioned at the highest point, and is "open" to the air.

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Floor-standing boiler
A floor-standing boiler is positioned on the floor and is usually associated with a high-quality domestic hot water production system.
Forced flue boiler
A forced flue boiler has no installation restrictions. It can be installed in a home without a chimney or with an inoperative chimney. It simply requires an opening in an external wall, of approximately ten centimetres in diameter, for the horizontal or vertical forced flue to pass through. This consists of a double concentric tube : one brings in the new air, the other discharges the combustion products.

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GCV (Gross Calorific Value)
This is equal to the sum of the NCV and of the latent heat in the steam produced by the combustion. By condensing this steam, we can recuperate additional heat (from 10 to 15 %), which can result in an efficiency of over 100%.

Gentle heat
Good insulation (walls, windows, roof, pipes) and the ability of modern boilers to operate at a low temperature means that radiators can be supplied with heating water at 50°C, as opposed to the former 70 or 80°C. To use this process, "Gentle heat" radiators are requiered which supply a more regular, more uniform heat. Using this method, the temperature differences between floor and ceiling are virtually eliminated.

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Heating circuit
Heat is produced in a boiler, which is then sent to a water circuit and is propelled by a pipe network to the rooms that need to be heated. The accelerator accelerates the circulation of the water.

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Immersion heater / Bath-water heater
An immersion heater or a bath-water heater is a fully independant device, which separates heating functions from domestic hot water functions.

Independent tank
An independent domestic hot water tank is a tank which is connected to the boiler, but that can be positioned at a distance. Its capacity ranges from 150 to 950 litres.

Instant domestic hot water
Domestic hot water is “instant” when it is produced simultaneously to its use. In order to do this, a boiler needs to have a high enough power to meet this requirement. The process is therefore limited to relatively moderate flows in order to prevent the installation of very large equipment.

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Low temperature boiler
Modern "low temperature" boilers function by keeping average temperatures between 30 and 60°C. This has three advantages: provision of the required quantity of heat when it is needed, reduction of the boiler’s losses to ambient air and reduction in energy consumption.

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Mixing valve
The function of a mixing valve is to mix the water at the heating outlet with the return water, in variable proportions, in order to:

  • permanently adapt the temperature of the water that is sent into the heating body to a level lower than the boiler’s temperature (in floor heating installations, a 3-way valve is required to avoid damaging the panel with water that is too hot)
  • raise the temperature of the return water, to avoid the formation of condensation inside the boiler which reduces the risk of corrosion
  • render the circuits fully autonomous (temperature, programming).

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NCV (Net Calorific Value of combustibles)
This is the total quantity of heat produced by the combustion of an energy source. For example, the combustion of 1 litre of fuel oil or of 1m3 of natural gas produces approximately 10 kWh. This enables us to compare the cost of different energy sources.

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Outdoor sensor
The regulator has an outdoor sensor which measures the outdoor temperature. The regulator adjusts the heating temperature automatically according to variations in the climate.

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Pressure jet gas burner
This is a mechanical burner which diffuses gas / air in the combustion chamber. This process is typically used in medium and high-power installations, and less so in low-power ones. It can be used to transform a fuel oil burner into a gas fired boiler.
The power of a boiler (in kiloWatts), refers to the useful output effectively transmitted to the heating water inside the boiler. Domestic boilers provide power between 10 and 50 kW of usefull output. Above this level, we get boilers of medium or high power, destined for use in large homes, collective accommodation, administrative buildings, schools or even small and medium-sized businesses.

Polluting emissions
This is the residue released by the combustion of gases, essentially carbon monoxide (CO2) and nitrogen oxide (NOx), which both contribute to the Greenhouse effect. Modern boilers consume far less energy and provide a much cleaner combustion, emitting three times less polluting substances than old-generation boilers.

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Room temperature sensor
The control system modulates the boiler’s temperature according to information that it collects from different sensors and pre-set comfort requirements. However it does not control the outcome, i.e. the ambient temperature. One option is to install a room temperature sensor in a neutral area of the house, away from sunlight, draft and far away from a radiator. This sensor is linked up to the control system and adjusts it according to the real ambient temperature. An alternative option is to install a thermostatic valve on all the radiators to regulate the temperature emitted by the radiator.

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Safety unit on an independent tank
Fitting a safety unit at the cold water inlet on a domestic hot water accumulation tank is compulsory. The safety unit provides three functions :
•    a safety valve which discharges excess water that is created during the heating process
•    a stop valve
•    a drain valve.

Safety unit of a heating circuit
On installations with a closed water circuit, the safety unit has three key components : the manometer which indicates the pressure of the water in the installation, the safety valve which prevents overpressure, and the bleeding device which is used to discharge air trapped in the pipes. 

Single function (boiler)
A single function boiler is generally used as a heating-only installation and does not have incorporated hot water production. It can however be used with an independent domestic hot water tank.

Smoke circuit
The smoke circuit is the path taken by the smoke through to the exit. A long smoke circuit with several bends allows for quiet operation.

Stainess steel
The heating body for floor-standing boilers can be made of cast iron or stainless steel. The thick steel (4 mm) used by De Dietrich guarantees a high resistance to mechanical stress.

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This is a process where the hot water produced by the boiler is moved around by the difference in density. This process is only applied to installations that use solid fuel (wood or coal).

Thermostatic valve
The thermostatic valve directly controls the flow of the radiator’s hot water on which it is assembled in order to achieve a desired temperature. It adapts to the ambient temperature of the room in which it is installed. It is particularly useful for rooms with other heat sources (sunlight, cooking equipment...).

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Wall-hung boiler
A wall-hung boiler is a particularly suitable heating solution for apartments or smaller houses. It can be used for domestic hot water production. It responds to  a need for space saving. It is more compact and lighter than a floor-standing boiler and frees up floor space. It can be installed easily in a kitchen, bathroom, cupboard or attic.

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