A furnace is a machine with two inputs and one output, and most players run it badly for years without noticing, because the cost is spread thin. Here is what fuel is actually worth, which furnace to use, and why coal is not the answer.
The three furnaces
Furnace. Smelts everything. Eight items per fuel unit at standard speed, which for coal means eight items per piece.
Blast furnace. Ores, metal tools and armour only. Twice the speed, half the items per fuel. Same total fuel cost per item, half the time.
Smoker. Food only. Same trade as the blast furnace – twice as fast, half the yield per fuel unit.
The trade is explicit and it is the first thing to understand: the specialised furnaces do not save fuel. They save time, and they cost the same fuel per item as a plain furnace. If fuel is scarce, the plain furnace is not worse. If time is scarce, it is.
The practical arrangement is a blast furnace for ore, a smoker for food, and a bank of plain furnaces for everything else – stone, sand, clay and the things neither specialist handles.
What fuel is actually worth
Fuel value is measured in items smelted, and the spread is wider than most people assume.
- Lava bucket – the highest value single item in the game by a wide margin. If you have an infinite lava source, fuel stops being a consideration entirely.
- Coal block – nine coal’s worth in one slot, which matters for hopper-fed setups where slot space is the constraint.
- Coal and charcoal – identical values. Charcoal is renewable and coal is not.
- Dried kelp block – slightly better than coal per item and fully renewable from a kelp farm.
- Planks, logs, sticks – low value each, but free in quantity. Sticks are the worst ratio in the game and the most common thing people burn.
The charcoal point is the one worth acting on. Charcoal is made by smelting logs, and a furnace running on charcoal to make more charcoal is a net gain – one batch produces far more fuel than it consumed. That closes the loop permanently and it costs a sapling.
Why coal is the wrong long-term answer
Coal is what you use for the first ten hours and what you should stop using after that.
It is finite, it competes with torches, and it requires mining trips. Charcoal from a tree farm and dried kelp from a kelp farm are both renewable, both automatable, and neither needs you to go anywhere.
The exception is the coal block, for bulk storage rather than for the fuel itself. Nine coal in one slot is the reason automated smelters are fed blocks rather than pieces – a hopper feeding single coal runs out of slot throughput long before it runs out of fuel.
Experience, which people forget to collect
A furnace stores experience for everything it smelts and releases it when the output is collected. That storage is unlimited in time and it caps per furnace.
Two consequences. Emptying a furnace by hand gives you the experience; a hopper pulling output into a chest gives you nothing. And a furnace left full for an hour is a battery you can cash in when you need levels.
Different items give different amounts. Ore smelting is worth the most, which is another argument for the blast furnace bank. The experience guide covers where that sits against other sources – the short version is that a smelting array is a better XP source than mining is.
What not to smelt
Iron, gold and copper ore should be smelted. Diamond, emerald, coal, lapis and redstone should not – they drop the item directly and smelting the raw block only applies where a raw form exists.
Smelting ore with Fortune is the mistake that costs the most. Fortune multiplies drops on ores that drop items directly, and does nothing for ores that drop a raw metal. Silk Touch plus smelting is not better than plain mining for iron and gold, and it is strictly worse for the ores where Fortune applies. The ore distribution guide covers which is which.
A working setup
- Tree farm feeding a furnace that makes charcoal. This is the fuel supply and it is the only one you need.
- Blast furnace bank for ore, hopper-fed from a chest, with output collected by hand when you want the experience.
- One smoker beside the kitchen. Food volumes are small enough that a bank is unnecessary.
- Four to six plain furnaces for stone, sand and glass, which is where building materials come from and where the volume actually is.
- Feed fuel as coal or charcoal blocks, not pieces.
Point five is the one that fixes an array that keeps stalling. A hopper moves one item at a time regardless of what that item is worth, so feeding blocks multiplies your throughput ninefold for free – the same throughput logic that governs any hopper-based system.
Images: Artifacts project gallery.