The shaft furnace technology has been the outcome of the efforts to overcome the shortfalls of the bucket preheating techniques.  It uses the energy obtained by the post-combustion to heat the scrap.  This technology has evolved in stages.  With a single shaft furnace at least 50% of the scrap can be preheated whereas a finger shaft furnace (involving a shaft with a scrap retaining system) allows preheating of the total scrap amount. A further modification is the double shaft furnace which consists of two identical shaft furnaces positioned next to one another and which are serviced by a single set of electrode arms (Worrell et al., 2010. p. 94).

The exact energy savings depend on the scrap used, and the degree of post-combustion (oxygen levels). For the finger shaft furnace tap-to-tap times of about 35 minutes are achieved, which is about 10-15 minutes less compared to EAF without efficient scrap preheating. The process may reduce electrode consumption, improve yield by 0.25 to 2 percent, increase productivity by 20 percent, and decrease flue gas dust emissions by 25 percent. (US EPA, 2010. p.36)

These technologies require close control of carbon monoxide and oxygen concentrations in order to reduce the risk of explosions.