Fuel

Fuel

Used by: Melter, Smeltery

Hephaestus Forge does not have a separate fuel recipe type. Fuel is declared inside hephaestus:melting recipes any fluid used as the fuel field of any melting recipe is automatically recognized as a valid fuel, and its temperature is derived from the highest temperature value found across all recipes that use it.

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How It Works

When a fuel fluid is placed in the fuel tank (below the Melter, or inside the Smeltery), the machine searches all loaded melting recipes for any recipe that declares that fluid as its fuel. The highest temperature found among those recipes becomes the fuel's effective heat output.

Fuel temperature = max(temperature) across all MeltingRecipes where fuel.id == this fluid

This means:

• A fluid used in a recipe with temperature: 800 provides 800° of heat.
• If the same fluid also appears in another recipe with temperature: 1400, it provides 1400° instead.
• The temperature is not hardcoded it is always the maximum across all recipes that reference that fluid as fuel.

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Vanilla Fuels

These fuels are registered by default via the built-in melting recipes:

Fluid	Temperature	Notes
minecraft:lava	800	Base fuel for most recipes
hephaestus:molten_blaze	1000	Higher tier fuel

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Registering a Custom Fuel

To register a new fuel, simply create a melting recipe that uses it in the fuel field. The recipe itself defines both the fuel fluid and the temperature it provides.

Via JSON (datapack)

{
  "type": "hephaestus:melting",
  "ingredient": {
    "item": "minecraft:netherite_ingot"
  },
  "result": {
    "id": "hephaestus:molten_netherite",
    "amount": 90
  },
  "fuel": {
    "id": "alltheores:soul_lava",
    "amount": 10
  },
  "temperature": 2000,
  "time": 200
}

This registers alltheores:soul_lava as a fuel with 2000° of heat, and also defines a melting recipe that uses it.

Via KubeJS

ServerEvents.recipes(event => {
  event.custom({
    type: "hephaestus:melting",
    ingredient: { item: "minecraft:netherite_ingot" },
    result: { id: "hephaestus:molten_netherite", amount: 90 },
    fuel: { id: "alltheores:soul_lava", amount: 10 },
    temperature: 2000,
    time: 200
  })
})

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High-Temperature Fuels

There is no hardcoded upper limit on temperature. You can register a fuel at any temperature value including extreme values like 20000.

{
  "type": "hephaestus:melting",
  "ingredient": { "item": "minecraft:ancient_debris" },
  "result": { "id": "hephaestus:molten_ancient_debris", "amount": 810 },
  "fuel": { "id": "alltheores:soul_lava", "amount": 10 },
  "temperature": 20000,
  "time": 400
}

Warning: A fuel registered at a very high temperature will be able to process all melting recipes with a lower temperature requirement. There is no way to restrict a fuel to specific recipes only if a recipe's temperature is less than or equal to the fuel's heat output, it will be processed.

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JEI Integration

Fuels appear automatically in the Melting and Smeltery JEI categories. No additional registration is needed any fluid that appears as fuel in at least one loaded melting recipe will be shown in JEI as a valid fuel, alongside its effective temperature.

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Notes

• fuel.amount is consumed once when the recipe completes, not per tick.
• If multiple fluids are available in the fuel tank, the machine selects the one with the highest temperature that still satisfies the current recipe's requirement.
• To add a modded fluid as fuel without making it melt a specific item, create a melting recipe for a cheap or common item (e.g. minecraft:cobblestone) and use it as an anchor.

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