Furnaces

Furnaces process raw ores into usable metal plates and other refined materials. You place an ore and a fuel into a furnace and it produces plates after a few seconds. This is one of the first production steps you set up, and it stays central to your factory throughout the game.

Furnaces are square buildings that have no rotations. Items can be added or removed manually or using inserters. Additionally, mining drills can directly drop their outputs into adjacent furnaces.

Furnaces as burner machines

The stone and steel furnaces are burner machines, meaning they run on solid fuel types. The group of burner machines also includes boilers, burner inserters, cars, and locomotives.

All burner machines share the same fuel rules:

They accept wood, coal, and various processed fuels such as solid fuel, with higher-quality fuels lasting proportionally longer.
A burner machine pauses burning when it has nothing to do, so fuel is never wasted while it sits idle.
Half burned fuels are lost if you pick up the machine.

Stone furnace

The stone furnace is the first furnace you have access to. It is a 2 by 2 building that takes a fuel item and a smeltable ore and outputs a plate. It holds up to one stack of each. You can use inserters to feed in fuel and ore automatically, and a separate inserter to pull out the finished plates. Inserters cannot remove fuel or unprocessed ore from a furnace.

Stone furnaces also appear as an ingredient in several early crafting recipes, so it is worth keeping a supply of them handy.

Steel furnace

The steel furnace is the same size and works the same way as the stone furnace, but it runs at twice the speed. If you are fuel-feeding a smelting line anyway, swapping stone furnaces for steel furnaces is a straightforward upgrade that doubles throughput without changing the layout.

Electric furnace

The electric furnace runs on electricity rather than solid fuel, which means no fuel inserter and no fuel belt needed. This simplifies your smelting layout considerably. It is a 3 by 3 building and also runs at twice the speed of a stone furnace.

Its more significant advantage is compatibility with modules and beacons, which become available with advanced research. These allow you to push furnace speed and efficiency well beyond what burner furnaces can achieve. For large-scale late-game smelting, the electric furnace is the standard choice.

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