How to Build an Auto-Smelter
A hopper-fed furnace bank that smelts a full chest of ore while you do something else — plus how much fuel you actually need.
Smelting a double chest of iron one furnace at a time is the kind of chore that makes people quit a world. An auto-smelter fixes it: dump raw ore in the top, fuel in the side, and come back to a chest of ingots.
How a furnace talks to hoppers
This is the whole trick, and it is worth understanding rather than copying:
- A hopper feeding into the top of a furnace fills the smelting slot.
- A hopper feeding into the side of a furnace fills the fuel slot.
- A hopper underneath a furnace pulls the finished item out.
Three hoppers, three jobs, decided entirely by which face they touch. Nothing else about the furnace needs configuring.
The single-furnace version
Start here even if you plan to build a bank of eight, because the wiring is identical.
- 1.Place your furnace.
- 2.Put a hopper on top of it, feeding down into the furnace. Put a chest on top of that hopper — this is your ore input.
- 3.Put a hopper against the side of the furnace, feeding in. Put a chest on top of that hopper — this is your fuel input.
- 4.Put a hopper underneath the furnace, feeding into a chest — this is your output.
Sneak while placing hoppers so you attach them to the block instead of opening it. Point a hopper by sneak-clicking the block you want it to feed into.
That is a complete working auto-smelter. Everything past this point is just scale.
Scaling to a bank
For serious volume, run a line of furnaces with a hopper chain above them and another below.
- The top hopper line runs horizontally, each hopper feeding into the next, with each furnace hanging below one hopper. Items travel along and drop into furnaces as they pass.
- The bottom hopper line collects from all the furnaces and runs into one output chest.
- Fuel gets its own hopper line along the side, or you feed each furnace by hand if you are using a slow fuel.
Eight furnaces is the usual sweet spot: fast enough to clear a mining trip, small enough to fuel without a dedicated farm.
Fuel, and how much you need
Every ordinary smelt takes 10 seconds. What differs is how many smelts each fuel gives you:
- Coal or charcoal — 8 items each.
- A block of coal — 80 items, and the most compact fuel to store.
- Dried kelp block — 20 items, and fully renewable from a kelp farm.
- Lava bucket — 100 items, the best per-slot fuel, but you get the empty bucket back in the fuel slot and it clogs the chain.
- Blaze rod — 12 items.
- Wood, planks, saplings — 1 to 2 items each. Bad fuel individually, but effectively free from a tree farm.
Charcoal is the practical answer for most players: smelt logs into charcoal, use the charcoal to smelt everything else, and the loop sustains itself from a tree farm forever.
Useful additions
A full-chest cutoff. Put a comparator on the output chest and use it to stop the input hopper when the chest fills. Saves you finding items scattered on the floor.
Smelt-only-what-needs-it. Feeding a whole mining haul in means cobblestone gets smelted into stone alongside your ore, burning fuel you wanted for iron. Sort the input first, or just be disciplined about what you throw in.
XP collection. Furnaces store experience and release it when you take items out by hand. If you let hoppers empty every furnace, you lose all of it. If XP matters to you, pull a few stacks manually — or get it from a spawner farm instead, which is far more efficient.
Blast furnace and smoker
Both smelt in 5 seconds instead of 10, at the cost of half the XP:
- Blast furnace — ores and metal only.
- Smoker — food only.
They accept hoppers exactly the same way, so build the same layout with blast furnaces if you are mostly smelting ore hauls, and a smoker bank next to your food supply.