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Technology of condensing gas boilers

Gas-fired condensing boilers do not only optimally utilise the supplied energy. Compared to conventional heaters, they also utilise the thermal energy contained in the flue gas, which is otherwise lost through the chimney.

Condensing boilers achieve a much higher efficiency and thereby reduce heating costs and emissions. Our gas-fired condensing boilers are of course also suitable for hot water preparation as well as heating.

The advantages of a Vaillant gas-fired condensing boiler:

  • Optimum energy efficiency of up to 98%
  • Significantly less soot and particulate matter during combustion via condensing technology
  • Consumption drops significantly compared to an old heating installation
  • Flexible expansion, e. g. with solar collectors, heat pumps, storage and controls

How a gas condensing boiler functions

In a gas-fired condensing boiler, the water is heated through the heat of combustion, just as with non-condensing boilers. The resulting flue gases are normally passed into the chimney. As a result, the energy contained in the flue gas is lost. However, condensing technology exploits these gases, which consist to a large extent of hot water vapour. It extracts the flue gas heat and feeds the energy obtained into the heating circuit.

In order to gain energy, water vapour must condense. It does this at a temperature of below 56 °C. The condensing boiler cools the steam through a specially designed heat exchanger. The energy gained is used to preheat the cold heating water. The hot water then passes into the primary heat exchanger where it is heated further to reach the desired temperature. During this process, small amounts of waste water occur which must be disposed of. The acidity of the waste water is so low that it can be conducted into a normal drainage system without further neutralisation.

The difference between upper and lower heating value

When talking about the high efficiency of 98 % of condensing boilers, the value refers to the "upper heating value". This must be distinguished from the "lower heating value" with which the industry usually makes its calculations. The lower heating value is the amount of heat that can be utilised in the combustion of an energy source, without causing condensation. The lower heating value therefore only contains a portion of the total fuel energy.

In contrast, the upper heating value also includes the amount of heat contained in the flue gas and water vapour which can be utilised by condensation. When accounting for the input energy the upper heating value take into account this extra heat. The efficiency of a heater is also called standard efficiency, can reach a maximum of 100% in the ideal case, when calculated on the basis of the upper heating value.