Sandustry Heat and the Thermal Buffer

Fire in this game has several sources — the Flamethrower and Lava are the two you meet first, and the section on charging below has the rest. The Thermal Buffer does not make heat — its description says it stores and distributes it — but it is the shared hub three machines point at when they describe their own fuel, so that is where this page starts.

The Thermal Buffer is the hub

The Thermal Buffer “stores and distributes heat for nearby machines”. That is the game’s own description, and it is what gives this system a shape: three other buildings describe their own fuel by pointing at it.

Three of them name it explicitly:

• The Burner Belt ignites flammable materials Officialwhen fuelled by heat through a Thermal Buffer
• The Pyro Dispenser fires a flame burst every 3 seconds Officialwhen fuelled by an adjacent Thermal Buffer — adjacent is the tightest placement word the research tree uses here; the Buffer itself only says “nearby”
• The Smelter smelts what is placed on top of it, Officialfuelled by heat from a Thermal Buffer or Lava

The Burner Belt and the Pyro Dispenser are described with the Buffer as their fuel and no other source named, so build it first. The Smelter is the one given a documented alternative — Lava — and the research tree gives it no prerequisites at all.

Each of the three got its own wiki page on 3 September 2026, and those pages settle what “nearby” means in practice: touching.

• Smelter: metal or ore touching its top, and at the same time a hot Thermal Buffer touching any other side, or Lava directly below it.
• Burner Belt: a flammable pixel touching its top, and a heated Buffer touching any other side. Without heat it is an ordinary belt.
• Pyro Dispenser: without heat from a Buffer it switches off and stops firing.

The Smelter page also makes the case for the Buffer over the Lava option: feeding a Smelter straight from Lava uses, on average, 2.5 times as much Lava as putting that Lava into a Buffer first. A Buffer can also sit wherever you like, while the Lava has to be directly underneath.

What each piece costs

The Buffer and the Burner Belt together are 1,500 Gold, both in tier 2 — automated ignition lands early and cheap next to tier 5’s Energy unlocks, which take 11,500 Gold to unlock as a set. The Pyro Dispenser is a tier-3, 2,000 Gold alternative that fires on a timer rather than igniting on contact.

Heat without the Buffer: trapped Lava

There is a heat source that needs no Thermal Buffer, and for burning Residue it is the one worth building first. It costs the Filter (250 Gold) and the Flamethrower (400 Gold) — the Flamethrower because only its direct flame melts Cinder back into Lava.

Put a solid Block directly under a Filter and anything that enters has no way out. Set the Filter to allow Cinder only, fill it, and ignite: the Cinders melt back into Lava and the Lava stays where you put it. Run Residue along the belt above and it ignites on contact.

Lava is also one of the two fuels the Smelter accepts.

Getting Cinders is a round trip through the cold side of this page: freeze Lava with Snow to make Scoria, break the Scoria with any weapon to get Cinders, carry them wherever you want. Cinder needs the Flamethrower’s direct flame to melt back — passive heat will not do it.

The slag processing page has the full auto-burner build.

The cold side, and why it is the same system

Every one of these is a documented conversion, and together they close a loop:

Start with	Apply	You get
Water	Fire	Steam, which rises and becomes rain
Ice	Fire	Water
Water	Snow	Ice
Lava	Snow	Scoria
Steam	Cold, via the Condenser	Water
Lava	A cold Thermal Buffer	Cinder
Water	Snowmaker, using Energy	Snow

Two tools drive most of it. The Flamethrower (tier 2, 400 Gold) burns residue, melts ice, and vaporises Water into Steam. The Cryoblaster (tier 2, 1,000 Gold) produces infinite Snow, which freezes water, solidifies Lava, or can be steamed into rain.

“Infinite” is the game’s own word for the Cryoblaster’s output, and it is the important one: your snow supply is not a resource you have to mine.

Drying & Condensing (tier 4, 2,500 Gold) unlocks two buildings at once. The Steam Dryer dries Amethelis and nothing else: Amethelis touching its top, Steam touching its bottom. The Condenser turns Steam into Water and Florin into Florinol, and it works the other way up: cold on top, from Snow or a cold Thermal Buffer, and the gas on the bottom. Running it off a Buffer costs 2 cold per conversion. Steam already returns on its own, since the game says it rises and becomes rain; the Condenser is what lets you decide where that happens instead of waiting for weather.

Charging the Buffer: two ways, and they are not equivalent

The Buffer absorbs heat from Fire and from Lava, and the difference between them is the decision this page exists to help you make.

Direct contact with Lava transfers a large amount of heat at once — and consumes the Lava. It is the fast way to fill a Buffer and it spends the resource doing it.

Fire transfers significantly less heat, and does not consume its source. Slower, but it runs indefinitely.

The wiki now puts numbers on both. Lava in direct contact gives the Buffer 250 units. Fire has a 40% chance of adding 1. That gap is the whole argument below. The cold side works the same way: Snow touching the Buffer takes it down by 20 units and uses up a large amount of Snow.

A cold Buffer treats Lava differently. Since v0.5.6, when the Buffer’s temperature is below zero, Lava touching it adds less heat and turns back into Cinder instead of being used up. The same patch stopped Buffers eating Lava inside artifact rooms, which had been soft-locking puzzles; an affected save repairs itself when it loads.

So the two are burst against sustain. A Buffer packed against a lava cell charges quickly and eats the cell; a Buffer sitting in fire charges slowly and keeps charging. Which you want depends on whether the machines downstream draw in bursts or continuously.

Fire is easier to come by than it looks. It comes from the Flamethrower and the Pyro Dispenser, it rises as occasional sparks off pools of Lava, and it is given off whenever anything burnable burns — Residue and Vines both count. A line that already burns Residue is already producing the heat source, which is worth knowing before you spend Lava on it.

Note that the Pyro Dispenser sits on both sides of this: it draws heat from the Buffer, and the fire it makes is itself a heat source. Nothing official describes the balance between those two, so treat it as a fact about the pieces rather than a design you can rely on.

What this page does not tell you

Earlier versions of this page said the Smelter, the Burner Belt and the Pyro Dispenser had no wiki pages and that the Buffer’s geometry was undocumented. Both are out of date: the pages exist, and the answer to geometry is contact.

What is still missing is capacity and draw: how much heat a Buffer can hold, and how much the Smelter, the Burner Belt or the Pyro Dispenser uses per operation. The only consumer with a published cost is the Condenser, at 2 cold per conversion. So 250 units tells you what a pixel of Lava puts in, but not yet how long that keeps a Smelter running.

Related

• Sandustry Slag and Residue Processing — the auto-burner in full
• Sandustry Energy Unlocks — the other supply system, and what runs on it
• Sandustry Research Planner — costing tier 2 against everything else
• How to Move Lava in Sandustry — a lava cell with water dripping on it is a Steam source that never runs down