An automatic smelter is not a redstone build. It needs no redstone dust, no repeaters, no comparators, and no power source at all. It is three hoppers placed around a furnace, and the entire design skill involved is understanding how hoppers move items and how furnaces consume fuel, not wiring anything. That makes it the most useful early build most players never get around to making, because it looks like a redstone project and isn't one.
This guide targets Minecraft 26.2 Java Edition. It is a spoke of the farm guides hub. If your smelter needs to run 24/7 without you standing there feeding it fuel, pair it with the bamboo farm guide for a renewable fuel supply, and route sorted ore and fuel into it using the same principles as the item sorter guide.
The three-hopper layout
A working automatic smelter is exactly three hoppers around one furnace, each doing a different job:
- A hopper feeding into the furnace's top slot, supplying raw material (ore, food, sand, whatever you're smelting). Furnaces only accept smeltable input through the top slot, so this hopper has to be placed directly above the furnace, facing down into it.
- A hopper feeding into the furnace's side slot, supplying fuel (coal, charcoal, lava bucket, wood, bamboo). The fuel slot is only reachable from the side, so this hopper sits beside the furnace at the same height, facing into it horizontally.
- A hopper pulling from the furnace's bottom, output slot, moving finished smelted items into a chest below. This hopper sits underneath the furnace, facing down into a chest (or another hopper line), pulling completed items out as soon as they finish.
Each hopper only interacts with the one furnace slot its position corresponds to: top for input, side for fuel, bottom for output. Get a hopper's position wrong, say, a second hopper on the other side instead of underneath, and it either does nothing or feeds the wrong slot, since fuel items and smeltable items are not interchangeable and the furnace will reject a mismatched item type in the wrong slot.
You do not need a chest above the input hopper. Hoppers can be fed directly by another hopper line, a minecart with a hopper, or simply thrown items on top with a small opening. The chest-on-top look in most screenshots is a convenience for manual loading, not a requirement of the design.
This layout has no moving parts and no redstone. Everything runs because hoppers automatically try to push items into any valid container they face, and automatically try to pull items out of any valid container above them, every tick they are able to.
Hopper transfer rate: the number that sets your ceiling
A hopper does not move items instantly or continuously. After every successful push or pull, it enters an 8 game tick cooldown, which is 0.4 seconds. That works out to a maximum transfer rate of 2.5 items per second per hopper, and that ceiling applies to each of the three hoppers independently: the input hopper feeding ore in, the fuel hopper feeding fuel in, and the output hopper pulling smelted items out all cap at 2.5 items/sec on their own transfers.
In practice this ceiling almost never matters for a single furnace, because the furnace itself is far slower than any of the three hoppers feeding or draining it, covered next.
Smelting time: the actual bottleneck
A single furnace smelts one item every 200 game ticks, which is 10 seconds, or 6 items per minute. Compare that to the input hopper's capacity of 2.5 items per second (150 items per minute) and the mismatch is stark: a lone furnace can only ever consume a small fraction of what a single hopper could deliver. The furnace, not the hoppers, is the bottleneck in every single-furnace build.
Blast furnaces and smokers cut that time in half: both smelt at 100 game ticks, 5 seconds per item, exactly twice the speed of a regular furnace. The trade is narrower input acceptance:
| Block | Smelt time | Accepts |
|---|---|---|
| Furnace | 10 sec/item | Everything smeltable: ores, food, sand, and more |
| Blast furnace | 5 sec/item | Ores and raw metals only |
| Smoker | 5 sec/item | Food only |
If your smelter exists to process ore, a blast furnace is a strict upgrade over a regular furnace, same hopper layout, double the throughput. If it exists to cook food, a smoker does the same job. A regular furnace is the only one of the three that handles both, which is why it remains the default for a general-purpose build.
Fixing the bottleneck: a multi-furnace array
Since one furnace can't come close to using a hopper's full transfer rate, the fix is not faster hoppers, it's more furnaces. A row of furnaces fed by the same input and fuel hopper lines multiplies total throughput almost linearly: 5 furnaces smelting in parallel process roughly 5 times the items per minute of one, while each individual furnace still only manages 6 items per minute on its own. The hoppers barely notice the extra load, since 2.5 items/sec per hopper is still well above what even a handful of furnaces will demand of it.
This is the actual lesson of the hopper-versus-furnace numbers: don't try to speed up item movement, add smelting capacity instead. A wall of blast furnaces, each with its own three-hopper set (or a shared input/fuel line down the row with individual output pulls), is the standard way to convert a large ore haul quickly.
Fuel math: what decides if your smelter keeps up
Every fuel item burns for a fixed time and therefore smelts a fixed number of items, since each item takes exactly 10 seconds (or 5, in a blast furnace or smoker) to process regardless of what's burning.
| Fuel | Burn time | Items smelted (furnace) |
|---|---|---|
| Coal | 80 sec | 8 items |
| Block of coal | 800 sec | 80 items |
| Lava bucket | 1000 sec | 100 items (bucket is returned empty) |
| Blaze rod | 120 sec | 12 items |
| Dried kelp block | 200 sec | 20 items |
| Raw bamboo | ~1-2 sec | 0.25 items (4 bamboo = 1 smelt) |
Raw bamboo is a very weak fuel item on its own, 4 pieces to smelt just 1 item. Crafting 9 raw bamboo into a bamboo block first raises that to 1.5 items smelted per block, still well behind coal, but it is the renewable option: a farm produces it with zero mining and zero Nether trips. See the bamboo farm guide for the full growth and fuel breakdown, including why raw bamboo and block-form bamboo are not the same fuel math.
The fuel math decides whether your smelter actually keeps up with its ore input, not the hoppers. A stack of 64 coal smelts 512 items, which at one furnace's 10-second pace takes over an hour and a half to burn through; at a five-furnace array it burns in under 20 minutes. If your input hopper is fed faster than your fuel can keep pace, unsmelted ore piles up waiting in the furnace's input slot, one item at a time, while the furnace idles between fuel loads. A lava bucket (100 items) or a block of coal (80 items) both dramatically reduce how often you have to refill the fuel hopper compared to loose coal, at the cost of needing that item in bulk up front.
Furnace XP: what happens when you hoover the output chest
Smelting stores experience inside the furnace rather than granting it immediately per item. When a hopper pulls items out of the output slot, that XP is not lost, it accumulates inside the furnace and is released the next time a player manually takes an item out of it. Breaking the furnace also drops whatever XP has accumulated inside it.
This has a real, easy-to-miss consequence: if your automatic smelter's output hopper feeds straight into a sorting system or a storage chest and you never manually pull an item from the furnace itself, that XP just sits there, uncollected, item after item, run after run. The fix is simple: periodically take at least one item by hand directly from the furnace's output slot (not from the chest downstream) to cash in the accumulated XP, or route the output hopper line so you occasionally intercept it by hand rather than letting it run fully automatic and out of sight.
The furnace is not slow because something is wrong with it. It is slow because 10 seconds per item is what it does, and the entire array design exists to work around that one fixed number.
Pros
- No redstone required, purely hopper placement
- Fully automatic once loaded: no standing at a furnace clicking items across
- Scales linearly by adding furnaces, not by any redstone complexity
- Blast furnace and smoker variants double throughput for their respective categories at no extra hopper cost
Cons
- A single furnace is badly bottlenecked against hopper transfer speed; needs an array for real throughput
- Fuel has to be manually maintained unless paired with a renewable source like a bamboo farm
- XP silently accumulates and is easy to leave uncollected if the output feeds straight into automated storage
- Blast furnace and smoker each only accept one category of input, so a mixed-use base still needs a regular furnace somewhere
Frequently asked questions
How many hoppers does an automatic smelter need?
Three per furnace: one on top feeding raw material into the input slot, one on the side feeding fuel into the fuel slot, and one underneath pulling finished items out of the output slot into a chest.
Why is my automatic smelter slow even with hoppers?
Because the furnace, not the hoppers, is the bottleneck. A hopper can move up to 2.5 items per second; a single furnace only smelts 1 item per 10 seconds, 6 per minute. Add more furnaces in parallel rather than trying to speed up hopper delivery.
Should I use a blast furnace or a smoker instead of a regular furnace?
If you are only smelting ores, a blast furnace smelts at 5 seconds per item instead of 10, twice the speed, for no extra hopper work. A smoker does the same for food only. A regular furnace is the only one that accepts both, and is the right choice for a general-purpose or mixed-use smelter.
What fuel should I use in an automatic smelter?
Coal smelts 8 items per piece, a block of coal smelts 80, and a lava bucket smelts 100 (and returns the empty bucket). For a renewable, zero-maintenance option, raw bamboo is very weak per item (4 bamboo per smelt) but a bamboo farm supplies it continuously with no mining trips.
Does an automatic smelter lose XP?
The XP from smelting accumulates inside the furnace rather than disappearing when a hopper pulls the output. It is only released when a player manually takes an item out of the furnace by hand, so a fully automated line that never gets touched by hand leaves that XP sitting uncollected until you break the furnace or take an item out yourself.
Can one hopper feed multiple furnaces?
A single hopper only outputs into whatever container is directly in front of its facing, so it can feed only one furnace's slot at a time. A row of furnaces needs its own input and fuel hoppers per furnace, though you can chain hopper lines so each one skims off items as they pass down the row.
An automatic smelter earns the "most useful build most players skip" label because it is genuinely simple, three hoppers and an understanding of where the bottleneck actually sits. Scale it into an array once one furnace stops keeping up, and check the farm guides hub for what to build next.
