Comparison Viessmann Vitopend 100-W A1HB 34 kW 34 kW vs Viessmann Vitopend 100-W A1JB 34 kW 34 kW

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.

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".

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.

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.

It is an operating mode designed for the warm season. In this mode, it works only to provide domestic hot water, and the heating is turned off. If the boiler is equipped with an outside temperature sensor, this sensor is also switched off in summer mode so that the heating does not turn on at night when the outside temperature drops.

The presence of a programmable thermostat in the design of the boiler.

Programmable thermostat is a device that allows not only to maintain the temperature but also to programme the operation of the boiler for a certain time. The simplest programmable thermostats cover a day, and more advanced ones allow you to set the operating mode for individual days of the week. Anyway, this function provides additional convenience and eliminates the need to adjust the operation of the boiler manually. On the other hand, the presence of a programmable thermostat affects the cost.

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.

— 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.

— 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.

— 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 heating 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.

The diameter of the pipe for connecting the pipe through which cold water is supplied to the boiler for heating and use in the hot water supply system.

Diameters are indicated in inches. It is allowed to connect a pipe of a different diameter through an adapter, but the best option is still a match in size. There are connection options 1/2", 3/4", 1" and 1 1/2".

The diameter of the pipe for connecting the pipe through which hot water leaves the boiler for the DHW system.

Diameters are indicated in inches. It is allowed to connect a pipe of a different diameter through an adapter, but the best option is still a match in size.