Steel furnace
Overview
The steel furnace is an early game smelting building that upgrades the stone furnace. It can be placed directly over an existing stone furnace by clicking the stone furnace with a steel furnace in hand, which replaces the old furnace and transfers all items inside it. Like all burner devices, it cannot be placed in space.
Compared with a stone furnace, the steel furnace keeps the same coal consumption rate but smelts twice as fast. This makes it a simple and immediate throughput upgrade for any smelting line that still uses burner furnaces. Its faster output is especially useful when a factory is limited by furnace count rather than fuel availability.
At normal operation, a steel furnace produces:
For comparison, a stone furnace produces each of the first three at 0.3125/sec and steel plate at 0.0625/sec, while coal consumption remains 0.0225/sec for both. This means the steel furnace doubles smelting speed without increasing fuel use per furnace, though the higher output also means ore lines and inserters must keep up with the increased demand.
Because it is still a burner furnace, the steel furnace remains part of the fuel-burning infrastructure and does not benefit from electric power. It is therefore most useful before a full switch to electric furnaces, or in situations where a simple furnace upgrade is preferable to redesigning the smelting setup.