Min. heat output
The minimum heat output at which the heating boiler can operate in constant mode. Operation at minimum power allows you to reduce the number of on-and-off cycles that adversely affect the durability of heating boilers.
Power consumption
The maximum electrical power consumed by the boiler during operation. For non-electric models (see Energy source), this power is usually low, as it is required mainly for control circuits and it can be ignored. Regarding electric boilers, it is worth noting that the power consumption in them is most often somewhat higher than the useful one since part of the energy is inevitably dissipated and not used for heating. Accordingly, the ratio of useful and consumed power can be used to evaluate the efficiency of such a boiler.
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.
DHW circuit max. pressure
The maximum pressure in the hot water circuit (DHW) at which it can operate for a long time without failures and damage. See "Heating circuit maximum pressure".
DHW min. T
The minimum temperature of domestic hot water (DHW) supplied by a dual-circuit boiler. For comparison, we note that water begins to be perceived as warm, starting from 40 °C, and in centralized hot water supply systems, the temperature of hot water is usually about 60 °C (and should not exceed 75 °C). At the same time, in some boilers, the minimum heating temperature can be only 10 °C or even 5 °C. A similar mode of operation is used to protect pipes from freezing during the cold season: the circulation of water with a positive temperature prevents the formation of ice inside and damage to the circuits.
It is also worth keeping in mind that when heated to a given temperature, the temperature difference ("ΔT") may be different — depending on the initial temperature of the cold water. And the performance of the boiler in the DHW mode directly depends on ΔT; see below for performance details.
Performance (ΔT=25°C)
The performance of a dual-circuit boiler in the DHW supply mode when the water is heated by 25 °C above the initial temperature.
Performance is the maximum amount of hot water the unit can produce in a minute. It depends not only on the power of the heater as such, but also on how much water needs to be heated: the higher the temperature difference ΔT between cold and heated water, the more energy is required for heating and the smaller the volume of water with which the boiler can handle in this mode. Therefore, the performance of dual-circuit boilers is indicated for certain options ΔT — namely 25 °C, 30 °C and/or 50 °C. And it’s worth choosing according to this indicator, taking into account the initial water temperature and taking into account what kind of hot water demand there is at the installation site of the boiler (how many points of water intake, what are the temperature requirements, etc.). Recommendations on this subject can be found in special sources.
We also recall that water begins to be felt by a person as warm somewhere from 40 °C, as hot — somewhere from 50 °C, and the temperature of hot water in central water supply systems (according to official standards) is at least 60 °C. Thus, for the boiler to operate in the ΔT=25 °C mode and produce at least warm water at 40 °C, the initial temperature of cold water must be at least 15 °C (15+25=40 °C). It is a rather high value — for example, in a centralized water supply system, cold water...reaches 15 °C, except in summer, when the water pipes warm up noticeably; the same applies to water supplied from wells. So this performance is a very conditional value. The boiler does not work so often with a temperature difference of 25 °C. Nevertheless, the data for ΔT=25°C is still often given in the specifications — including for advertising purposes since it is in this mode that the performance figures are the highest. In addition, this information may be useful if the boiler is used as a pre-heater, and heating to operating temperature is provided by another device, such as an electric boiler or instantaneous water heater.
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.
Combustion chamber
The type of combustion chamber provided in the boiler.
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Open(atmospheric). Combustion chambers of this type consume air from the room in which the boiler is installed, and the combustion products are naturally removed through the flue. Boilers of this design are simple and inexpensive but have specific installation requirements: the room must be well-ventilated, and the height of the chimney must be at least 4 m to ensure sufficient draft.
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Closed(turbocharged). Closed combustion chambers are isolated from the room in which the boiler is installed: combustion air is taken from the street, and combustion products are removed there. For this, a coaxial flue is usually used — in the form of two pipes nested one inside the other: combustion products are removed through the inner one, and the outer one is responsible for the air supply. Turbocharged combustion chambers are more complicated and expensive than open ones, and the maximum length of the chimney is limited. On the other hand, such a boiler does not burn the air in the room, and it can be installed anywhere, regardless of the ventilation efficiency.
— Is absent. Boilers powered by electricity do not have combustion chambers (see "Source of Energy").
