Rust Furnace Guide: Smelting Ratios, Large vs Electric & Wood Math

Every ore in Rust smelts 1:1 — one metal ore becomes one metal fragment, one sulfur ore becomes one sulfur, one high quality metal ore becomes one HQM. The furnace never changes what you get. What it changes is how fast the ore cooks and how much wood you burn doing it, and the gap between tiers is enormous: a Large Furnace smelts 5x faster than a standard Furnace on a fifth of the wood. This guide covers all three furnaces, the exact per-ore numbers, and the wood math for a real farm haul.

If you'd rather punch your stack size into a tool and get the answer, the smelting calculator runs these same numbers for any amount and any furnace count.

The Three Furnaces Compared

The standard Furnace is a default blueprint with no workbench requirement — you can craft one naked on the beach the moment you've farmed 200 stones, 100 wood, and 50 low grade fuel. The other two are Workbench Level 2 unlocks. The Large Furnace costs 60 scrap to research directly; the Electric Furnace is only 30 scrap, and it also drops from military, elite, and locked crates, so you'll often loot one before you ever research it.

The Per-Ore Numbers

These are the exact smelting rates for a single ore in each furnace, straight from our data:

Two things jump out. Sulfur is the fastest, cheapest smelt — half the time and wood of metal ore. And HQM ore is the slowest cook in the game, twice as slow as metal, which is why the HQM guide tells you to batch it and walk away.

The Wood Math on a Real Haul

Per-ore numbers are abstract, so here's what a farm run actually costs. A decent mining session brings home about 1,000 metal ore, 1,000 sulfur ore, and a handful of HQM ore:

Read that middle column again. The Large Furnace turns a near-hour metal smelt into eleven minutes and cuts the wood bill from 1,670 to 330. Its 500-stone, 600-wood, 75-low-grade craft cost pays for itself on the first serious ore haul — the wood you save smelting 1,000 metal ore alone nearly covers what the furnace cost to build.

Times above are for one furnace. Running several in parallel divides the clock (three standard furnaces smelt 1,000 metal ore in about 18 minutes), which is why early-wipe bases line up a row of cheap furnaces instead of waiting on one.

Charcoal: The Byproduct That Matters

Wood burned in a furnace comes back out as charcoal — not quite log-for-log, since a share of each burn is lost, but the bulk of your fuel bill returns as crafting material — and charcoal is the bulk ingredient in gunpowder. That means smelting sulfur ore is secretly the first half of making boom: the same furnace session that cooks your sulfur also banks the charcoal you'll mix it with. Don't dump your charcoal to make inventory space — it's ammunition you haven't crafted yet. The gunpowder guide covers the recipe and the ratios from there.

One wrinkle: the Electric Furnace burns no wood, so it produces no charcoal. If you're smelting sulfur for a raid, that's a real cost — you'll have to burn wood somewhere else (campfires work) to cover the charcoal side of the gunpowder recipe.

The Electric Furnace: Worth It?

The Electric Furnace is, as the game puts it, "an electrical version of a furnace that uses electricity instead of a fuel source." It draws just 3 rW — one of the smallest loads in the game, barely more than a ceiling light — so even a modest solar-and-battery setup can run a couple around the clock. Our power usage page has the full draw table if you're budgeting a circuit.

The case for it: zero wood, ever. Once it's wired, ore goes in and product comes out with no fuel runs, no restocking, no babysitting. At roughly 1.7x the speed of a standard furnace it's also quicker than the thing it replaces.

The case against: it's still 3x slower than a Large Furnace, and the no-charcoal problem above. My verdict — the Electric Furnace is a convenience upgrade, not a throughput upgrade. It's superb as a set-and-forget metal smelter in a base that already has power, and it frees your wood income for building. But when a raid stack of sulfur needs cooking, the Large Furnace is still the tool.

Automating Your Smelting: The Industrial Setup

Once your base has power, furnaces stop needing you at all. Two cheap Workbench Level 1 components do the work: the Storage Adaptor (100 metal fragments) snaps onto a furnace or storage box to expose its inventory, and the Industrial Conveyor (75 metal fragments) moves items between adapted containers, with filters so you can tell it exactly what to carry.

The classic loop: a drop box of raw ore feeds through a conveyor into your furnaces, and a second conveyor pulls the finished fragments and sulfur out into sorted storage. Dump a full mining haul in one box, walk away, and come back to smelted product filed where it belongs. Pair it with an Electric Furnace and the whole chain — fuel included — runs on your power grid, or wire an igniter into a bank of wood furnaces instead. The Large Furnace is the throughput king here too, with room for multiple adaptors on one placement. Circuit basics are in the electricity guide, and the power usage table will tell you what the full setup draws.

Placement and Workflow Tips

• chevron_rightFurnace light is a beacon. A lit furnace glows, and at night that glow tells everyone on the horizon that your base is occupied and worth raiding. Smelt behind walls, and think twice before running furnaces overnight in a visible spot early wipe.
• chevron_rightGive the Large Furnace its own space. It's a big, tall placement that goes on open ground, not on foundations — plan a walled courtyard or a ground-floor opening for it inside your tool cupboard range rather than trying to squeeze it into an upstairs hallway. Bases that want one indoors get designed around it from the first foundation.
• chevron_rightDon't bother splitting stacks. Old Rust wisdom said to spread ore across every slot for parallel smelting. That's dead: a furnace now works through its queue at a fixed rate no matter how the ore is stacked. The speed lever that still works is running more furnaces side by side.
• chevron_rightWire an igniter. A 2 rW Igniter lets you light furnaces remotely on a switch or timer — pair it with an Electric Furnace setup and your whole smelting operation runs from one button. The electricity guide covers the circuit basics.
• chevron_rightMatch the furnace to the wipe stage. Day one: two or three standard furnaces, they're nearly free. The moment you hit Workbench Level 2 with 60 scrap spare, research the Large Furnace — it's one of the highest-value researches in the game. Add an Electric Furnace once your power grid is up, and keep the Large for bulk sulfur.

Plug your own numbers into the smelting calculator before your next farm run — knowing the wood bill in advance means you farm exactly enough and cook it all in one pass.