Following the sucessful introduction of the Bessemer process for producing steel, the Siemens process was devised. It can be regarded as an updated and enlarged version of the puddling process but producing steel rather than wrought Iron. Gas or heavy oil were used as fuel and these and the combustion air were preheated using the exhaust flue gases. The flame is directly above the hearth and is fired from alternative directions in order to make best use of the preheaters. A Siemens furnace can be charged with molten pig iron, solid pigs or scrap steel. Alloying and refining can take place before the Steel is teemed and cast.

The majority of the structure of a Siemens open hearth furnace is fire brick. This required total replacement on a regular basis. Although long since replace in the U.K. by BOS and electric arc furnaces, other countries, such as the USA seem to have perpetuated their use.