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Department for Business, Energy and Industrial Strategy

Boiler Controls and Recovery

Examples of typical cost and energy savings for each technology can be found in the technology information leaflet on this page.


The Energy Technology List (ETL) offers two different types of controls for boiler systems. These are aimed at ensuring boilers operate at their most efficient level, and produce heat only when and where it is needed.

1. Burners with Controls:

  • Products that are specifically designed to create and burn air and fuel mixtures in a safe, efficient and controlled manner, and to direct the heat released through combustion into a pressurised vessel (or other combustion chamber).

2. Retrofit Burner Control Systems:

  • Products that are specifically designed to automatically control, in an energy efficient manner, the operation of industrial and commercial burners, and the matching of burner heat production with heat demand.

Burners with Controls

Burners with controls are used to provide heat for hot water, steam and thermal oil boilers, heaters and processes. They are widely used in industry and commerce. Mounted on a furnace, a burner com­bines air, fuel and ignition energy in the right proportion and admits the fuel–air mixture into the furnace, where the combustion reaction takes place. A burner has three main functions:

  • Flame stability
  • Air-fuel mixing
  • Emission control

A selected range of burner systems designed to recover combustion exhaust gas heat are also available. The Energy Technology List aims to encourage the purchase of products that are able to accurately control combustion and maintain their efficiency over a specified operating range. Eight different categories of burners with controls are covered, and products that are designed to use liquid or gaseous biofuels are also covered by these categories.

The level of improvement that can be achieved by upgrading burners depends on the age and design of the boiler system. Fuel savings of 3%-5% may result from upgrading to burners whose heat output is modulated to ensure that it matches the heat demand.  The benefits are greatest in applications where the output needs to be frequently adjusted to meet variations in demand.

Retrofit Burner Control Systems

A range of retrofit burner control systems are available, and these offer different levels of precision and repeatability of control.

Heat Recovery for Boiler Systems

The ETL offers three different types of heat recovery for boiler systems.

1. Condensing Economisers:

  • Are products specifically designed to improve boiler net thermal efficiency by recovering both sensible and latent heat from boiler flue gases.​​​​​​

2. Non-condensing Economisers:

  • Are products that are specifically designed to improve boiler net thermal efficiency by recovering sensible heat from boiler flue gases.

3, Heat Recovery from Flash Steam and Boiler Blowdown Condensate:

Covers products that are specifically designed to recover heat from steam condensate and / or water from boiler blowdown, by means of heat exchangers and/or flash steam recovery vessels.

Condensing Economisers

Economiser plant is used in a wide range of industrial and commercial applications, and are used in applications where lower grade heat is required or with hot water boilers with low return temperatures (<60oC). Fitting an economiser to a boiler can increase the net efficiency by 9% across different boiler output ratings. Condensing economisers are able to recover more heat by recovering both sensible heat and latent heat of evaporation, cooling flue gases below the dew point. This heat is normally used to preheat the boiler’s feed water and to supply low grade heating requirements.

Non-condensing Economisers

Non-condensing economisers recover heat from the boiler flue gases before they are released to the atmosphere. This allows the heat to be recycled, and raises boiler system efficiency. Installing a specified energy saving ETL flue gas economiser can provide fuel savings of more than 3%.

Non-condensing economisers are more likely to be deployed where higher temperature heat recovery is required such as steam boilers (and pre-heat of condensate return), in applications: food manufacturing, chemical industries, oil refineries, paper industry, laundries, hospitals and prisons.

Non-condensing economisers are a type of heat exchanger that enables some of the sensible heat in boiler flue gases to be recovered. This heat is normally used to preheat the boiler’s feed water.

Heat Recovery from Flash Steam and Boiler Blowdown Condensate

The ETL encourages the purchase of heat recovery equipment that is specifically designed to recover heat from steam condensate and/or water from boiler blowdown.