Condensing boilers

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Condensing boilers are highly efficient technologies, capable of providing heat to buildings as well as domestic hot water. They are called ‘condensing’ because they  ‘condense’  the  water  vapour  produced  in  the  combustion  process  into liquid form. The heat of the water vapour is reused to warm up the cold water entering the boiler. This process ensures that most of the energy produced during combustion is recovered to heat the building. 

The most common condensing boilers operate with gas, while condensing boilers running on other fuels are especially suited for off-grid buildings. Condensing boilers can easily be teamed with a solar thermal system to reduce fuel consumption by 10-20%. The use of condensing boilers with green gases (such as biomethane, hydrogen and bio-LPG) and fuels would enable further COemissions reductions,  moving  us  closer  to  our  EU-wide  goal  to decarbonise the building sector by 2050.

Our market data shows that condensing boilers running on gas remain the first choice in efficient heating technology in Europe. They are particularly suitable for the modernisation of existing appliances as  they can rely on an existing, and extensive, gas network. More than 4 million of them were sold in 2018, bringing substantial energy efficiency gains compared to the old and inefficient systems they replace. The highest energy efficiency gains are obtained by installing a condensing boiler and adjusting the system where needed thanks to hydronic balancing and the possible addition of heat emitters.


  • Ready for green gases.
  • Up to 35% CO2 emissions reductions when replacing non- condensing technology.
  • Around 20% energy efficiency gains by modernising the heating system.
  • 3 Easy combination with renewable heating and solar thermal.
  • Gas condensing boilers rely on existing gas network.
  • Potential to further reduce greenhouse gas emissions with green gases, like biomethane and hydrogen.