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.
Rated current
The current consumed by the electric boiler (see "Power source") during normal operation.
This parameter directly depends on the power. It is required primarily for organizing the connection: wiring and automation must safely deal with the current consumed by the unit.
Coolant min. T
The minimum operating temperature of the heat medium in the boiler system when operating in heating mode.
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.
Flue diameter
The diameter of the pipe through which combustion products are discharged from the combustion chamber.
In boilers with a closed combustion chamber often used the coaxial flue, consisting of two pipes nested one inside the other. At the same time, products of combustion are discharged from the combustion chamber through the inner pipe, and the air is supplied through the gap between the inner and outer ones. For such flues, the diameter is usually shown in the form of two numbers — the diameter of the inner and outer pipes, respectively. The most popular values are
60/100,
80/80 and
80/125. Non-coaxial flues can be
100,
110,
125,
130,
140,
150,
160,
180 and
200 mm.
Max. gas consumption
Maximum gas consumption in the boiler with the corresponding energy source (see above). Achieved when the gas heater is operating at full capacity; with reduced power and consumption, respectively, will be lower.
Note that boilers of the same power may differ in gas consumption due to the difference in efficiency. While the more fuel-efficient models tend to cost more, the price difference pays off in gas savings.
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.
Heat exchanger
The material of the primary heat exchanger, in which thermal energy from hot combustion products is transferred to the heat medium. The efficiency of the boiler, the heating rate and the service life of the unit directly depend on the material of the heat exchanger.
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Copper. Copper is a material with the best heat dissipation specs and high corrosion resistance. It heats up quickly, which allows you to save energy during the operation of the heating boiler, has a low roughness coefficient, and has a long service life. The only drawback of this metal is its high cost. Copper heat exchangers are installed in heavy mid-range and premium grade equipment.
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Aluminium. Aluminium as a heat exchanger material is characterized by excellent thermal conductivity and long service life. Moreover, it is cheaper than
copper. To reduce the cost of production in copper heat exchangers, they try to reduce the wall thickness. You don't need to do this with aluminium.
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Cast iron. Boilers with a cast-iron heat exchanger heat up for a long time and cool down slowly, retaining heat for a long time after heating stops. Cast iron is also notable for its high heat capacity and low susceptibility to corrosion. The service life of a cast iron unit can be 30 or 50 years. The reverse side of the coin is the huge weight and size of hea
...ting equipment, which is why boilers with cast-iron heat exchangers are produced mainly in floor-standing boilers. In addition, cast iron does not tolerate sudden temperature changes — they can cause cracks.
— Steel. Steel heat exchangers in heating boilers are the most widely used. Steel has a combination of high ductility and strength when exposed to high temperatures, is inexpensive, and can be easily processed at production stages. However, steel heat exchangers are susceptible to corrosion. As a result, they are not as durable.
— Stainless steel. Stainless steel heat exchangers are rare in heating boilers, which is explained by the high cost of using this material. But they combine the advantages of both cast iron and steel. Stainless steel exhibits high corrosion resistance, resistance to thermal shocks, low inertia, and long service life.
