Air preheater

The air preheater uses the hot feed water to preheat the combustion air and obtain a cool water flow in the return. This cold flow can now be used in an additional economiser bundle to further reduce the flue gas temperature. This increases efficiency by 2% points, or flue gas temperatures that are roughly 40K lower.

As the air preheating utilises the combustion air as internal heat sink, the increased efficiency is fully reflected in the reduction in annual fuel costs.

Info on Air preheater


The Bosch air preheating system consists of:

  • A second economiser bundle which is delivered mounted on the boiler or supplied loose with the boiler depending on the transport dimensions
  • A heat exchanger for air preheating
  • The necessary valves and sensors for shutting off and controlling the system
Bosch air preheating system

Bosch air preheating system

Steam boiler


Flue gas heat exchanger stage 1



Heat exchanger, combustion air


Flue gas heat exchanger stage 2


Temperature controller



3-way valve


Combustion air


Feed water