Type
Depending on the set of functions, boilers are divided into single-circuit and dual-circuit.
-
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.
Heating area
A very conditional parameter that slightly characterizes the purpose based on the size of the room. And depending on the height of the ceilings, layout, building design and equipment, actual values may differ significantly. However, this item represents the maximum recommended area of the room 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 especially 50-year-old houses. Accordingly, this item is more of a reference nature and does not allow us to fully assess 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; For more information on this, see "Useful Power". In our case, the heating area is calculated using the formula “boiler power multiplied by 8”, which is approximately equivalent to use in houses that are several decades 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.
Remote control unit
Remote control unit that allows you to control the boiler from another room. It can be connected both wired and wirelessly, often equipped with an electronic display to indicate operating modes, set temperature, emergency situations, etc. Many of these units are advanced devices with the ability to programme the operation of the boiler, for example, for a week; some models can be equipped with temperature sensors that automatically adjust the intensity of the boiler depending on the temperature in the room.
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.
