The Stone Furnace is what turns raw ore into metal in Permafrost. Without it, the copper and iron you mine just sit in your backpack doing nothing, and the whole path toward Wire, a working radio, and better tools stays locked. It smelts ores into ingots and also lets you cook Coal out of Wood, so it is the piece you want up early at your base.
Quick answer: Raise your Building skill to level 3, press U, open the Building tree, and hold the left mouse button on the Stone Furnace to spend 2 blueprint points. Gather 40 Stone, then place it from the Utilities tab of the build menu.
What you need before you start
The blueprint tree keeps the furnace locked until Building reaches level 3. Placing structures raises that skill, so there is no need to grind for it. On Story difficulty, placing a foundation, bed, workbench, wall, and roof was sufficient to take Building from its starting level to level 3.
- Building skill level 3, reached by placing a handful of wooden pieces
- 2 blueprint points free to spend
- 40 Stone carried in your inventory
- The Building Tool (the hammer) equipped
Unlock the Stone Furnace blueprint
Where to get the 40 Stone
With a Flint Pickaxe, Rock Boulders gave 6 or 7 Stone each on Story difficulty, so six or seven boulders cover the cost. Loose Rock Shards also count, and it takes forty of them to reach 40.
Build the furnace
The Stone Furnace needs no foundation and no roof. The preview turns green on bare snow, and it works fine out in the open air.
If the preview hangs off the ground you will see “CAN’T BUILD IN AIR.” Tilt the camera down until the outline drops onto the snow. If you are a Stone short, the preview reads “MISSING RESOURCES” instead.
Open it and smelt copper, iron, and coal
Walk up to the built furnace and the prompt reads “Stone Furnace, Press F Open.” Pressing F opens its panel, and that panel confirms the whole thing worked. Three recipes are listed inside. The costs below were read on Story difficulty; another world’s panel showed 5 Wood for Coal (x2) and 3 Iron for an Iron Ingot, so read the numbers on your own panel.
| Recipe | Ingredients |
|---|---|
 Coal (x2) | 3 Wood |
 Copper Ingot | 3 Copper, 5 Coal |
 Iron Ingot | 2 Iron, 3 Coal |
Coal does double duty here. You can mine it from Coal Boulders with a Flint Pickaxe, where one boulder gave 7 Coal, or cook it at the furnace itself, where 3 Wood yields 2 Coal. If you came home with plenty of ore but no fuel, burning Wood into Coal saves a second trip.
The ingredient tooltips give you a sense of what is worth smelting. Copper is valued at 15 and Iron at 20, Coal sits at 16, Wood at 5, and both the Copper Ingot and Iron Ingot come out at 40 each.
Where Copper comes from and what the first ingot is for
You can mine Copper Boulders with a Flint Pickaxe; one sits deep in the first cave, off the main trail. After smelting your first Copper Ingot, craft Wire at the Workbench for 1 Copper Ingot. The Radio Station Bench calls for 3 Wire and 10 Wood, so that first ingot goes toward getting the radio running.
