Condensing gas boiler technology for central heating

If you have a boiler in your home, you might be interested to learn that condensing boilers are slowly but surely replacing older designs in the powering of domestic central heating systems. This is happening especially in Europe but is filtering around North America and down to Oceania.

The switch to condensing boilers has been strongly advocated by pressure groups and government bodies who are concerned with reducing energy use. In comparison with conventional boilers, gas-fired condensing boilers do not only optimally utilise the supplied energy but, they also utilise the thermal energy contained in the flue gas, which is otherwise lost through the chimney.

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What makes a condensing boiler different to a non-condensing boiler? Both types of boilers heat water through the heat of combustion. With a non-condensing boiler, the resulting flue gases are normally passed into the chimney and, as a result, the energy contained in the flue gas is lost. However, condensing boiler technology exploits these gases, which consist to a large extent of hot water vapour and extracts the flue gas heat and then feeds the energy obtained into the heating circuit.

The water vapour must condense in order to gain energy. This is temperature specific and a condensing boiler works well at a temperature of below 56 °C. The condensing boiler cools the steam through a specially designed heat exchanger. The energy gained is then 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 waste water has very low amounts of acidity and requires no processing before it can be drained into a normal drainage system.

Condensing boilers achieve a much higher efficiency than non-condensing boilers and thereby reduce your heating costs and emissions. A basic rundown of benefits from a condensing boiler are:

  • Optimum energy efficiency of up to 98%
  • Significantly less soot and particulate matter during combustion via condensing technology
  • Consumption drops by up to 30% compared to an old heating installation
  • Low investment costs
  • Flexible expansion, e. g. with solar collectors, heat pumps, storage and controls

When talking about the high efficiency of 98 % of condensing boilers, the value refers to the “upper heating value”. Technicians in the boiler industry usually make their calculations using the “lower heating value”. 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 and does not give a full picture of the efficiency of a product.

The upper heating value will also include the amount of heat contained in the flue gas and water vapour which can be utilised by condensation. The efficiency of a boiler is also called standard efficiency, and this can reach a maximum of 100% in the ideal case, when calculated on the basis of the upper heating value.

If you install a condensing boiler there may be the need to supplement your existing chimney with a small plastic pipe. These can be easily fitted to existing chimneys as they have a very small diameter.

New technology always has its advantages over old technology and installing a condensing boiler in your home will see you benefit from:

  • Space savings: Condensing boilers don’t need a hot water tank and are available in a wide range of compact sizes, making them much sleeker and convenient to fit in a kitchen cupboard when compared to conventional models.
  • Supply reliability: New boilers are all fitted with a heat exchanger made from a non-ferrous metal, usually stainless steel, so that they don’t corrode over time. There is no need to wait for the hot water cylinder to refill, either, so hot water is available in unlimited supply.
  • Simple controls: Conventional boilers tend to operate fairly simply, with either a temperature on/off switch of a controller with a few standard heating options. However, condensing boilers don’t need a timer, as they automatically produce hot water whenever a tap is turned on.


Whether running in condensing mode or not, a condensing boiler will always be 15-30% more energy-efficient than its conventional counterpart, helping you to reduce your energy bills while limiting the impact of your domestic heating on the environment.


As long as your new condensing boiler is properly installed and maintained by a certified gasfitter, it will undoubtedly prove to be a reliable, cost-effective and energy-efficient investment for your home.