Type
Depending on the set of functions, boilers are divided into single-circuit and dual-circuit.
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Single-circuit boilers are equipped with one heat exchanger, in which the heat from fuel combustion is transferred to the heat medium of the heating system. The only function of such boilers is space heating. It is technically possible to use single-circuit boilers to provide hot water, but this requires an additional tank (the so-called indirect water heater).
- In
dual-circuit boilers, the primary heat exchanger is supplemented by a secondary one. Due to this, such a boiler, in addition to heating the room, also provides a hot water supply. In this case, both running water and water accumulated in a special tank(see Built-in water heater tank) can be used.
Power supply
The type of electrical supply required for normal operation of the boiler. Power supply may be required not only for electric models but also for other types of boilers (see "Power supply") — in particular, for the operation of control automation. Connection options can be:
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230 V. Work from a household system with a voltage of 230 V. At the same time, models with a power consumption of up to 3.5 kW can be connected to a standard outlet, but for high consumption devices, you need to connect directly to the distribution board. Many of the electric boilers with this connection also allow operation from 400 V (see below).
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400 V. Operation from a three-phase system with a voltage of 400 V. This power supply is suitable for boilers with any power consumption. However, it is not as common as 230 V: in particular, it may be difficult to use it in a residential area. Therefore, this option is provided mainly in high-power devices for which a 230 V power supply is not suitable.
— Autonomous work. Work in completely autonomous mode, without an electricity connection. This format of operation is found in all boilers that do not use electrical heating (see "Energy source"), except for purely liquid fuel ones — in them, electricity is necessary for the operation of the fuel supply systems.
Coolant min. T
The minimum operating temperature of the heat medium in the boiler system when operating in heating mode.
Coolant max. T
The maximum operating temperature of the heat medium in the boiler system when operating in heating mode.
Heating circuit max. pressure
The maximum pressure in the heating circuit of the boiler, at which it remains operational, and there is no risk of physical damage to the structure. For a heating system, the maximum pressure is usually about 3 bar, and for a domestic hot water circuit up to 10 bar. When the maximum pressure is exceeded, a safety valve is activated, and part of the water is discharged from the system until a normal pressure level is reached.
"Summer" mode
It is an operating mode designed for the warm season. In this mode, it works only to provide domestic hot water, and the heating is turned off. If the boiler is equipped with an outside temperature sensor, this sensor is also switched off in
summer mode so that the heating does not turn on at night when the outside temperature drops.
Heated floor mode
The boiler has a special
mode for underfloor heating systems.
Underfloor heating differs from conventional heating systems primarily by a
lower coolant temperature — otherwise the floor could be too hot for comfortable use (plus, high temperatures are also undesirable for flooring and furniture installed on it). In addition, boilers with this function are distinguished by increased pump power. In order to ensure efficient circulation of the coolant through branched heating circuits that have rather high resistance.
Efficiency
The efficiency of the boiler.
For electric models (see "Energy source"), this parameter is calculated as the ratio of net power to consumed; in such models, indicators of 98 – 99% are not uncommon. For other boilers, the efficiency is the ratio of the amount of heat directly transferred to the water to the total heat amount released during combustion. In such devices, the efficiency is lower than in electric ones; for them, a parameter of more than 90% is considered good. An exception is gas condensing boilers (see the relevant paragraph), where the efficiency can even be higher than 100%. There is no violation of the laws of physics here. It is a kind of advertising trick: when calculating the efficiency, an inaccurate method is used that does not take into account the energy spent on the formation of water vapour. Nevertheless, formally everything is correct: the boiler gives out more thermal energy to the water than is released during the combustion of fuel since condensation energy is added to the combustion energy.
Expansion vessel capacity
The capacity of the expansion tank supplied with the boiler.
The expansion tank is designed to drain excess water from the heating system when the total volume of liquid increases as a result of heating. It consists of two parts connected by a flexible membrane: in one, hermetically closed, there is air under pressure; in the other, excess water enters, compressing the membrane. In this way, a catastrophic increase in pressure in the heating circuit is avoided. The optimal volume of the expansion tank depends on several system parameters, primarily the volume and composition of the coolant; detailed recommendations for calculations can be found in special sources.
