Heating area
The maximum area of the building that the boiler can effectively heat. However, it is worth considering that different buildings have different thermal insulation properties and modern buildings are much “warmer” than 30-year-old and even more so 50-year-old houses. Accordingly, this paragraph is more of a reference nature and does not allow a full assessment of the actual heated area. There is a formula by which you can derive the maximum heating area, knowing the useful power of the boiler and the climatic conditions in which it will be used; see Heat output for more details. In our case, the heating area is calculated according to the formula "boiler power multiplied by 8", which is approximately equivalent to use in houses that are more than a dozen years old.
Condensing
Boilers generate additional heat by condensing water vapour from combustion products. In such units, the combustion gases, before entering the flue, are passed through an additional heat exchanger, in which they are cooled, and the water vapour condenses and transfers thermal energy to the coolant. It allows you to increase the efficiency by 10 – 15% compared to boilers of the classical design — up to the fact that in many similar models, the efficiency exceeds 100% (for more details, see "Efficiency").
The condensation principle of operation is most often found in gas models (see "Power source"); however, solid and liquid fuel boilers with this feature are also produced.
Built-in water heater tank
The presence of a built-in water heater tank in the boiler — a storage tank for water used in the hot water supply system. For obvious reasons, this feature is found exclusively in dual-circuit boilers (see "Type"). It provides several advantages over a flow-through design (when the boiler heats water directly in the process of moving through the heat exchanger). Firstly, in the tank, you can constantly keep a supply of ready hot water, and use it even in case of interruptions in the water supply. Secondly, the temperature of the dispensed water is constant, while in instant heating devices fluctuations are possible when the water flow rate changes. Thirdly, the efficiency of work does not depend on the pressure in the water supply. On the other hand, this feature significantly affects the dimensions, weight and price of the boiler.
DHW tank volume
The volume of the DHW tank provided in the boiler.
In this case, we can talk about both built-in tanks (see above), and a separate device supplied in the kit. The first option is found in dual-circuit boilers, and the second is in single-circuit ones (see "Type"). Anyway, the larger the tank, the more water you can keep in reserve, but the larger and heavier the entire boiler or separate tank is. There are special methods that allow you to calculate the optimal tank capacity depending on the number and type of water points, the number of users, etc. Such methods are described in detail in special sources, but we note here that the average value is considered to be about 80 – 100 litres. It is enough for regular use by a family of 3 – 4 people.
Heat output
It is the maximum useful power of the boiler.
The ability of the device to heat a room of a particular area directly depends on this parameter; by power, you can approximately determine the heating area, if this parameter is not indicated in the specs. The most general rule says that for a dwelling with a ceiling height of 2.5 – 3 m, at least 100 W of heat power is needed to heat 1 m2 of area. There are also more detailed calculation methods that take into account specific factors: the climatic zone, heat gain from the outside, design features of the heating system, etc.; they are described in detail in special sources. Also note that in dual-circuit boilers (see "Type"), part of the heat generated is used to heat water for the hot water supply; this must be taken into account when evaluating the output power.
It is believed that boilers with a power of more than 30 kW must be installed in separate rooms (boiler rooms).
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.
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.
DHW max. T
The maximum temperature of domestic hot water 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). Accordingly, even in the most modest models, this figure is about 45 °C, in the vast majority of modern boilers, it is not lower than 50 °C, and in some models, it can even exceed 90 °C.
Also 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 ~30 °C)
The performance of a dual-circuit boiler in hot water mode when water is heated by approximately 30 °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 ΔT — namely 25 °C, 30 °C and/or 50 °C. And it is 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 mode ΔT ~ 30 °C and give out at least warm water at 40 °C, the initial temperature of cold water should be about 10 °C (10 + 30=40 °C). A similar temperature can be found in wells in the warm season, and cold water in the ce...ntralized water supply system often warms up to 10 °C in the warm season. However, boilers, including dual-circuit boilers, are switched on mainly in cold weather, when the initial water temperature is noticeably lower. Accordingly, if the boiler is used as the main water heater, heating to the claimed temperatures (see "DHW min. T", "DHW max. T") often requires a greater ΔT than 30 °C, and the performance is less than indicated in this paragraph. But when operating in the preheating mode (when the water is heated to the desired temperature by an additional device like a boiler), this parameter describes the capabilities of the unit very reliably.
