text: The first successful economizer design was used to increase the steam-raising efficiency of the boilers of stationary steam engines.  It was patented by Edward Green in 1845, and since then has been known as Greens economiser.  It consisted of an array of vertical cast iron tubes connected to a tank of water above and below, between which the boilers exhaust gases passed.  This is the reverse arrangement to that usually but not always seen in the fire tubes of a boiler; there the hot gases usually pass through tubes immersed in water, whereas in an economizer the water passes through tubes surrounded by hot gases. While both are heat exchange devices, in a boiler the burning gases heat the water to produce steam to drive an engine, whether piston or turbine, whereas in an economizer, some of the heat energy that would otherwise all be lost to the atmosphere is instead used to heat the water and/or air that will go into the boiler, thus saving fuel. The most successful feature of Green's design of economizer was its mechanical scraping apparatus, which was needed to keep the tubes free of deposits of soot.
  Economizers were eventually fitted to virtually all stationary steam engines in the decades following Greens invention.  Some preserved stationary steam engine sites still have their Greens economisers although usually they are not used.  One such preserved site is the Claymills Pumping Engines Trust in Staffordshire, England, which is in the process of restoring one set of economisers and the associated steam engine which drove them. Another such example is the British Engineerium in Brighton & Hove, where the economiser associated with the boilers for Number 2 Engine is in use, complete with its associated small stationary engine. A third site is Coldharbour Mill Working Wool Museum, where the Green's economiser is in working order, complete with the drive shafts from the Pollit and Wigzell steam engine.