Smelting and spoilage (furnaces, food, fuel)

Heat is the heart of Rust's mid-game economy. Every metal fragment, every sulfur grain, every cooked steak passes through a fire. This guide locks down the math: what burns, what cooks, how fast, and how long the result keeps before it kills you.

1. Furnace tiers

Rust offers five heat sources for smelting and cooking, each tuned for a different stage of the wipe.

The standard Furnace smelts all loaded slots simultaneously, so stacking three full slots of metal ore is 3x more wood-efficient than running one. The Large Furnace widens that gap further: ~40% wood per metal frag, ~80% for sulfur, ~33% for HQM compared to a standard furnace.[^rl-furnace][^rl-large] The Electric Furnace consumes 5 rW continuously while on, has only a single combined input/output slot, but never needs wood, making it the centerpiece of any industrial-crafter base.[^rl-elec][^ch-elec]

1a. Heat-source deep dive — start to finish

Picking the wrong furnace early-wipe quietly bleeds wood and time. Walk the ladder in order: the Campfire is your day-one heat source — 5 wood to deploy, learned by default, no workbench required. It carries a single ore slot plus a fuel slot, so it is only ever a stopgap for the first 10 metal ore and a few steaks. The Refining Small Furnace is a deliberate trap for new players: despite the name it cannot smelt ore at all — it exists purely to convert crude oil into Low Grade Fuel. Researching it costs ~200 wood (research-table cost), and it has no place in your smelting pipeline.

The standard Furnace is the genuine workhorse. At 50 stone and 25 LGF it is cheap enough to deploy two or three side by side, and its three ore slots smelt fully in parallel — there is no penalty for filling all three, only a 3x throughput gain on identical wood-per-minute. The Large Furnace is the bulk-economy unlock: 600 stone, 100 wood and 4 LGF buys you 18 ore slots and a dramatically better fuel ratio. The Electric Furnace is the end-game piece — it trades wood for a continuous ~3-5 rW electrical draw and a single combined slot, but it smelts roughly 40% faster than a wood furnace, never produces charcoal, and can be wired into a fully automated loop.

One subtle point that costs new players charcoal: the Electric Furnace produces zero charcoal. If gunpowder is your priority, keep at least one wood furnace running even after you electrify — the charcoal byproduct of a normal smelt run is effectively free fuel for explosives. Conversely, if you have ample charcoal banked, the electric furnace's wood-free operation is pure profit.

2. Smelt rates per ore

Rust's smelting ratios are all 1:1 by stack count — the difference is time per unit and charcoal yield.

Practical benchmark: a standard furnace burns through 1000 wood + 600 metal ore → 600 metal fragments + ~750 charcoal, taking roughly 33 minutes of fuel.[^rl-furnace][^rusttips] Large furnaces hit the same 600 frags on ~400 wood. HQM is the bottleneck — it smelts at one third the speed of metal ore, which is why HQM-heavy clans run banks of electric furnaces instead.

2a. Why HQM is the throughput bottleneck

The 1:1 stack ratio hides the real cost: time. A metal or sulfur ore clears in roughly 5 seconds, but an HQM ore takes around 15 seconds — three times longer for the same single slot. A standard furnace with all three slots packed with HQM ore therefore outputs HQM at one third the rate it would output metal fragments. This is the single biggest reason serious bases run dedicated banks of furnaces split by ore type rather than mixed loads.

• Never mix ore types in one furnace if you can avoid it — the slowest ore (HQM) does not slow the others, but tracking mixed output is error-prone and you will pull half-smelted stacks.
• Dedicate a furnace per resource: one for metal, one for sulfur, one for HQM. This makes output boxes predictable for industrial conveyors.
• HQM belongs in electric furnaces. The ~40% speed boost matters most where smelt time is longest — a bank of three electric furnaces churning HQM around the clock at zero wood cost is the standard clan setup.
• Sulfur belongs in large furnaces. The large furnace burns roughly 80% of a standard furnace's wood per sulfur unit — modest, but on 10,000+ sulfur ore for a raid that is thousands of saved wood.

Quick reference for full-furnace batches (all slots loaded, standard furnace): 3 metal ore finish a cycle in ~5 s; 3 sulfur ore in ~5 s; 3 HQM ore in ~15 s. The large furnace runs the same per-unit times but with 18 parallel slots, so a single load can smelt 18 HQM ore in one ~15-second tick — the parallelism, not raw speed, is what makes it scale.

3. Fuel economy

Wood is the universal fuel for stone-and-mortar furnaces; Low Grade Fuel (LGF) powers tool cupboards' modded cousins and weapons, not furnaces. The relevant numbers:

• 1 wood = 2 seconds of burn in any wood-fed furnace (30 wood/min in a standard furnace).[^rl-furnace]
• 2 wood per 30-second smelt tick — so a single metal ore (5 sec) consumes ~0.17 wood; a sulfur ore is identical; an HQM ore (15 sec) costs ~0.5 wood.
• Sulfur math: 2.5 wood per sulfur ore in a standard furnace; 1000 sulfur ore needs ~2500 wood and ~28 minutes.[^hp-stack]
• LGF in refineries: the Small Oil Refinery converts 1 crude oil → 3 LGF, burning ~1 wood per LGF produced; budget 1000 wood for 344 crude.[^ch-cook]

Charcoal is essentially free — every furnace run produces ~0.75 charcoal per wood burned, which feeds gunpowder.

3a. Charcoal economy and the wood double-dip

Charcoal is the most under-appreciated byproduct in Rust. Every wood burned in a furnace or campfire has roughly a 75% chance to yield 1 charcoal, so a smelt run that consumes 1000 wood quietly hands you around 750 charcoal — enough for a substantial gunpowder stockpile, since gunpowder is crafted from charcoal and sulfur. The practical lesson: do not farm wood twice. Players who smelt metal and then go chop a separate wood pile for charcoal are doing double the work. Bank the charcoal that your metal smelt already produced.

• 1 wood = 2 seconds of burn in any wood-fed furnace, a flat constant across campfire, standard and large furnaces.
• Charcoal yield is per wood burned, not per ore smelted — long HQM runs that burn more wood also bank proportionally more charcoal.
• LGF is not furnace fuel. It technically combusts but the conversion is wildly inefficient; reserve LGF for chainsaws, jackhammers, flame weapons and the Refining Small Furnace's input chain.
• Refinery math: the Small Oil Refinery converts 1 crude oil into 3 LGF, burning roughly 1 wood per LGF produced — budget about 1000 wood to refine ~344 crude into ~1000 LGF.

A common mistake is leaving a furnace over-fuelled. Wood keeps burning even after all ore is smelted, so topping a furnace with 500 wood for a 100-ore job simply wastes ~400 wood as pure heat. Fuel to the job: roughly 2 wood per 30-second tick, scaled to your ore count.

4. Cooking meats and calories

All raw meats cook on a campfire or any furnace at 30 seconds per piece; leaving them past ~60 seconds produces Burnt Meat (low calorie, no penalty but wasteful).

Bear is king for calories per slot; fish is king for hydration; chicken is king for accessibility.[^ch-cookbear][^thegamer]

4a. Where to cook — campfire vs BBQ vs Cooking Workbench

Cooking has its own tier ladder, separate from smelting. The Campfire cooks up to 4 pieces of food at once at ~30 seconds each. The Barbeque (BBQ) is the dedicated cooking upgrade — it offers far more slots (around 12 total), still cooks meat at ~30 seconds and fish faster at ~20 seconds, and burns wood efficiently at roughly 1 wood per 10 seconds. For feeding a group or stockpiling cooked meat before a raid, the BBQ is the correct tool; a furnace technically cooks food too but ties up valuable ore slots.

Post-Cooking 2.0, the Cooking Workbench consolidates the old Mixing Table and BBQ into one advanced station. It handles standard meat cooking plus advanced recipes — teas, temperature teas (hot tea to cool down, cold tea to warm up), and multi-ingredient dishes that combine the new farmed crops, eggs and honey. New direct-consumption foods carry meaningful stats: wheat gives roughly +75 calories and +6 healing, eggs around +40 calories and +15 hydration, and jars of honey about +50 calories with a small radiation reduction.

4b. Burnt food and the over-cook penalty

Leaving meat on heat past its cook window does not destroy it — it produces Burnt Meat (or Burnt Chicken/Fish). Burnt food is edible and carries no poison debuff, but it delivers far fewer calories than a properly cooked piece, so it is pure waste. With a campfire or BBQ this is easy to avoid: pull food at the ~30-second mark, or simply load only as much as you can monitor. Cooked meat is always strictly better than raw — about triple the spoilage life and a small health tick on consumption — so the rule is cook everything you are not eating in the next minute, but don't walk away and let it char.

5. Spoilage timers

Every meat enters its spoilage timer the instant it lands in a container or inventory — corpses on the ground don't tick. Timers do NOT reset on transfer.[^ch-spoiled]

Spoiled meat is not deletable loot — it still carries ~30% calories but adds a poisoning debuff that drains health. Players cannot reverse spoilage.

5a. How the spoilage clock actually works

Spoilage is a per-item timer, and understanding its exact rules prevents most food losses. The clock starts the moment food enters any lootable container — your inventory, a box, a furnace, a corpse. Food sitting in a freshly-killed animal carcass on the ground does not tick, which is why you should butcher only when you are ready to process. Critically, the timer does not reset on transfer: moving meat from your inventory into a box, or out of a box into a fridge, carries the elapsed time with it. A piece that has been raw for 15 minutes goes into the fridge with 15 minutes already spent.

• Cooking pauses and extends, it does not reset. Cooked meat gets a fresh, longer timer (~60 min vs ~20 min raw), so cooking is the cheapest preservation action available.
• A powered fridge freezes the timer outright — items inside never tick down. But because timers do not reset, an item already half-spoiled when it goes in will be half-spoiled when it comes out.
• Spoiled food is not deleted. It becomes Spoiled Meat/Fish — still worth a fraction of its original calories, but it applies a poisoning debuff that drains health. Spoilage cannot be reversed.
• Items now display a visible spoil timer in their tooltip, so you can triage a box of meat at a glance and eat the oldest first.

Note on numbers: spoilage timings have shifted across wipes. Older guides cite multi-hour raw-meat life; current builds run far shorter raw timers (on the order of ~20 minutes in inventory) with cooked meat lasting roughly an hour. Treat all timer values as approximate and confirm against the live build, because Facepunch tunes these regularly.

6. Preservation strategies

• Cook everything immediately. Cooked meat lasts ~3x longer than raw and weighs the same.
• The Fridge is the only true preservation tool. A powered fridge (≥5 rW) freezes the spoilage timer entirely — items inside never tick down, but the timer does not reset when removed.[^ch-fridge]
• Cold biomes do NOT slow spoilage in 2026 — snow zones only affect player temperature and hypothermia, not food chemistry. (Common myth.)
• Animal Fat and Plant Fiber items ignore spoilage entirely; hoard fat between wipes.
• Canned food purchased from vending machines or scavenged from food crates never spoils — keep a stash for raid nights.

6a. Building the electric-furnace automation loop

The fully hands-free smelting loop is the payoff for unlocking the power grid. The chain is: a storage box of raw ore feeds an Industrial Conveyor, which pipes ore into one or more Electric Furnaces; a second conveyor pulls the smelted output (fragments, sulfur, HQM) into an output box or directly into an Industrial Crafter for auto-crafted ammo and components. Because the electric furnace needs no wood, this loop runs continuously — including while you are offline — as long as the power holds.

• Power budget: each electric furnace draws on the order of 3-5 rW while active. Three furnaces plus conveyors comfortably fit on a modest solar-and-battery array; add a generator or large battery bank for night-time and offline coverage.
• Gate power with a memory cell: wire the furnace so it is powered only when ore is present, switching off when the input box runs dry. This avoids burning power on an empty furnace.
• Filter conveyors by item: set the conveyor to move only ore in, and only the smelted product out, so metal, sulfur and HQM lines stay cleanly separated.
• Split by ore type: dedicate furnace lines per resource just as with wood furnaces — it keeps output boxes predictable and lets the slow HQM line run without throttling metal.

The trade-off to accept: this loop produces no charcoal at all. Keep one wood furnace in rotation for gunpowder supply, or bank charcoal heavily before going fully electric.

7. Animal fat economy

Animal fat is Rust's bottleneck medical resource. The full chain:

• Medical Syringe: 20 metal frags + 20 animal fat + 30 cloth → 1 syringe (20 sec craft).[^rl-syringe]
• Large Medkit: ~52 animal fat + 20 metal frags + 18 cloth + 2 syringes → 1 medkit (30 sec craft).[^rl-medkit]
• Bandage / Anti-Radiation Pills: cloth-only, no fat.

Net: one bear (~20 fat) = ~1 syringe + change. One large medkit eats ~92 fat (52 direct + 40 from two syringes). A 10-hour raid run requires 5+ medkits = ~500 fat = ~25 bear kills or ~100 wolves. This is why long-game clans cook bear fat in industrial loops.

7a. Fat sourcing and the animal kill ladder

Animal fat never spoils, which makes it the one food-chain resource you can safely hoard across an entire wipe. The catch is yield: fat per kill scales hard with animal size. A bear drops the most (roughly 5-20 fat), a boar or wolf a handful (~2-5), a deer similar, and chickens almost nothing. With each Medical Syringe costing ~20 fat and each Large Medkit eating ~92 fat all-in, a raid-night medical loadout of five medkits demands roughly 500 fat — about 25 bear kills, or four-to-five times that many wolves.

• Hunt bears first for fat efficiency — one bear can be worth twenty chickens of fat.
• Process kills with a Bone Knife or better; higher-tier tools pull more resources per carcass.
• Bank fat in any box — no fridge needed, it never ticks down.
• Cook bear meat in industrial loops so the fat accrues passively while you do other things.

7b. The ten most common smelting and food mistakes

Avoiding these saves more resources than any optimization:

• Trying to smelt ore in the Refining Small Furnace — it physically cannot; it only makes LGF.
• Running a single ore slot in a 3-slot furnace, wasting two thirds of your wood-per-minute.
• Over-fuelling a furnace so wood keeps burning after the ore is done.
• Smelting bulk sulfur in standard furnaces instead of large furnaces (~80% the wood cost).
• Smelting HQM in wood furnaces when electric furnaces would be ~40% faster.
• Farming wood a second time for charcoal that the metal smelt already produced.
• Storing raw meat overnight — cook before logging off, every time.
• Letting meat char into low-calorie Burnt Meat by walking away from the campfire.
• Assuming cold/snow biomes slow spoilage — they do not; only a powered fridge does.
• Forgetting that spoilage timers do not reset on transfer or when leaving a fridge.

8. Pro tips

1. Electric Furnace + Industrial Conveyor + Industrial Crafter is the end-game smelt loop. Pipe metal ore from a storage box into an electric furnace, pipe output into the crafter, and walk away with auto-crafted ammo and components.
2. Never store raw meat overnight. Cook first, then fridge. Even one offline hour can spoil unguarded raw stacks.
3. Sulfur in Large Furnaces only. Standard furnaces cost ~80% more wood per sulfur unit.
4. HQM in Electric Furnaces only if you have steady solar/generator power. Three electric furnaces produce HQM continuously at zero wood cost.
5. Charcoal stacks of 1000+ are easy to accumulate while smelting metal — save the wood-burning byproduct for gunpowder runs instead of farming wood twice.
6. Buy canned food at outposts for travel kits — no spoilage, no fridge required, and bandit/outpost vendors restock predictably.
7. Stack three slots of ore in a standard furnace before lighting it; you'll smelt 3x the volume on the same wood per minute.
8. Don't burn LGF in a furnace. It works but is wildly inefficient — save LGF for jackhammers, chainsaws, and weapons.

9. Sources

[^rl-furnace]: Furnace — Rust Wiki (Fandom) [^rl-large]: Large Furnace — Rust Wiki (Fandom) [^rl-elec]: Electric Furnace — Rust Wiki (Fandom) [^ch-elec]: Electric Furnace — Corrosion Hour [^rusttips]: Rust Furnace Calculator — Rusttips [^hp-stack]: Furnace and Refinery Stack Efficiency Guide — HubPages [^ch-cook]: RUST Cooking, Smelting & Refining Guide — Corrosion Hour [^ch-cookbear]: Cooked Bear Meat — Corrosion Hour [^thegamer]: Rust: 10 Best Food Items — TheGamer [^ch-spoiled]: Spoiled Fish Meat — Corrosion Hour [^ch-fridge]: RUST Fridge — Corrosion Hour [^rl-syringe]: Medical Syringe — Rust Wiki (Fandom) [^rl-medkit]: Large Medkit — Rust Wiki (Fandom)

Want more? Industrial Crafters · Food, Water & Healing