More Furnaces Special Furnace Mechanics

Two furnaces behave differently from the others:

• Netherrack Furnace - does not use any fuel at all. Instead it must be activated by placing fire on top of it, after which it smelts very slowly (1800 ticks per item, about 0.11x vanilla speed). Because it relies on fire placement rather than fuel input, it cannot be supplied fuel by ordinary automated methods. It is useful as a free, hands-off smelter when speed is not a concern.

• Obsidian Furnace - can smelt two items at once while using the same amount of fuel as smelting a single item. This effectively doubles its throughput, giving it an effective speed of about 2.66x (roughly 75 ticks per item) even though its base smelting rate matches the Copper and Iron furnaces.

The higher-tier furnaces (Silver, Gold, Diamond) gain their advantage from large numbers of input and output slots combined with high speed, letting them work through big stacks of ore quickly when supplied with enough fuel.