The batch is introduced at the front end of the furnace. At each side, up to 23 burner lances inject natural gas. The flames spread horizontally across the batch and cause it to melt at a temperature of 1550 ˚C. Powerful regenerators are found at each side of the furnace through which the hot combustion gases are channelled to the chimney. Every 20 minutes, the firing changes from one side to the other. The cold combustion air is directed through the currently hot regenerator, warming it up and thus winning back approximately 30 % of the energy.