Schematic drawing of a waste heat boiler economiser installed by ThermTech

Waste heat boilers are often used to raise steam or hot water by utilising the heat from hot gases exhausted by high energy equipment such as gas engines, turbines, incinerators and regenerating furnaces.

A waste heat boiler economiser can be retrofitted onto the exhaust ductwork of the boiler to further cool down exhaust gases and so preheat the boiler feed water. The uplift in boiler efficiency can be significant, resulting in a higher steam generation output. (Up to 20%)

Unlike natural gas fired steam boilers, the exhaust gases from the waste heat boiler can potentially reach much higher temperatures of 300 °C + and unlike a normal gas fired boiler, the flue gas flow does not modulate in proportion to the boiler feed water flowrate.

It is therefore necessary to introduce an automated exhaust gas bypass mechanism on the economiser. The bypass dampers are controlled by a thermostat located on the boiler economiser water outlet. This control loop helps prevent undesirable boiling from occurring inside the economiser tubes.


  • Bespoke design to suit the individual boiler system
  • Design conforms to BS EN 12952, the Pressure Equipment Directive (PED) and CE marked accordingly
  • Manufactured entirely from carbon steel as the most economical design
  • Highly durable extended surface fins spirally TIG welded around the outside of each boiler economiser tube. In applications where gases can potentially foul the economiser tubes with soot deposits, designs with wide spaced solid finned tubes, soot blower systems and cleaning access doors can be chosen
  • Single tube design ensuring a uniform boiler feed water flow through the entire tube element even on a high boiler turn down, avoiding undesirable local hot spots, scaling and sludge build up inside the boiler economiser tubes
  • Designed to minimise additional back pressure on the burner fan such that normal boiler operation is not affected.

ThermTech offer an initial on-site survey of your waste heat boiler system and can design a bespoke economiser system to suit.  See more about hot water boiler economisers ThermTech have supplied to our customers in our Case Study.

For waste heat boiler economiser enquiries, fill in the form and email it to or contact us.