Energy recovery for thermal technology

Energy recovery is indispensable in any steam, thermal oil, central heating and air technology system and comes in a myriad of forms. We create the right combination, tailored to your application, to usefully repurpose as much energy as possible and keep your energy consumption under control.

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Energy recovery boosts your heating system’s efficiency

Our energy recovery technologies will maximise your heating system’s efficiency. Some, such as economisers and condensers, are integrated into virtually all our designs because of their broad applicability and rapid efficiency gains.

Others, such as air preheaters and intercoolers, will only generate added value if specific preconditions are met. Our engineers will be happy to perform the calculations for you!

Another example? The automatic flue-gas pipe cleaners by our sister company Optimum by Callens are true technological feats that maximise efficiency and ensure that your boiler will always operate at peak capacity.


Analyse your options with the Energy Ladder

Energy recovery is the sum total of your personal context. To present you with the best energy recovery methods, we use the Energy Ladder.

  • What temperature do you require?
  • Can we recover heat from your production process?
  • Is there any biogas we can make use of?
  • Might an electric boiler prove worthwhile?
  • Is hydrogen an option as a fuel?

Go through the options with us and discover what minor adjustments can already lead to greater efficiency.

Pose your energy-recovery question

stoomketel met geintegreerde economiser

Project in the spotlight

To allow us to tick off the ‘optimised efficiency’ box, we fitted this new main steam boiler with an economiser, oxygen regulator and air preheater (APH). It keeps the production of chemical base components for its medicines safe and energy-efficient. 

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Callens energierecuperatie farma economiser luchtvoorverwarmer zuurstofregelaar

How energy recovery can reduce your energy bill

An economiser or flue-gas condenser allows us to recover heat from the flue gasses and reintegrate that heat into the thermal process. This technique alone can save you 5 to 10 % on energy and reduce your CO2 emissions.

Callens economiser


  • Ideal for steam
  • Thermal oil and central heating: possible
  • Saving ± 5 %
Callens condensor


  • Ideal for steam
  • Thermal oil and central heating: possible
  • Saving ± 7 %
Callens luchtvoorverwarmer

Air preheater

  • For every application, if appropriate
  • Saving ± 1 %
Callens frequentieregeling

Frequency regulation

  • Burner fan
  • Circulation or feed pumps
  • 30 to 40 % of the electric power
Callens zuurstofregeling

Oxygen regulation

  • For every application, if appropriate
  • Saving of 1 to 2 %
Callens HRSG

HRSG (= Heat Recovery Steam Generator)

  • For steam
  • Bonus: output and application dependent

Valorising revaporation steam

  • For steam
  • Bonus: output and application dependent

Water treatment

  • RO system
  • Thermal degassing
  • Recovery via the blowdown valve


  • For steam, central heating
  • Bonus: output and application dependent

An energy recovery system that takes account of your expectations

Every energy recovery system has its own selection criteria. Depending on your energy expectations, our design engineers choose one or a combination of the possible techniques. Perhaps an electric, hybrid or hydrogen boiler might even be of benefit to you?

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hybride stoomketel


To give you an idea of our expertise in energy recovery systems, here are some of our finest projects.