Economisers are gas-to-water heat exchangers located within a purpose-built flue section. They are used to recover heat from flue gasses for shell and water-tube boilers.

The main use of economisers is to pre-heat boiler feed water. An economiser can potentially be retro-fitted to most steam and high-temperature hot-water boilers, and there are also opportunities to fit economisers to conventional, non-condensing heating boilers.

Economisers require careful financial and technical consideration, so as to acquire the correct sizing. They are best paired with gas-fired boiler plants. Consideration should also be given to the space taken by economisers within the boiler room. It is advisable to contact a specialist boiler contractor to assess the feasibility and needs of the installation.