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.
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).
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 max. T
The maximum operating temperature of the heat medium in the boiler system when operating in heating mode.
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.
Warm start
Support for the warm start function by the boiler.
This function is found only in dual-circuit models (see "Type"): it accelerates the water heating for the domestic hot water system and ensures a constant leaving water temperature. To do this, the boiler automation monitors and controls the temperature of the water in the secondary heat exchanger of the boiler. The presence of a "warm start" affects the cost of the unit, but this is offset by the ease of use.
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.
