Furnace

Furnace is the block that turns one resource into another — ore into ingots, sand into glass, logs into charcoal, food into a meal — and the first one you place is usually still running late in a world. Everything it does costs fuel and time, worth knowing before you fill a furnace room.

Fuel is where the savings are. One piece of coal or charcoal smelts eight items, a block of coal smelts eighty, and a lava bucket runs for a hundred and hands the empty bucket back. Wood burns fast and poorly, which makes charcoal the honest answer to furnace fuel in survival: dedicate one Furnace to making charcoal and a tree farm feeds every other one forever. Dried kelp blocks do the same for kelp farmers.

Smelting also stores experience. A Furnace holds the levels earned by everything it has processed and hands them over the moment you take the output out by hand — one left running an hour is a small experience bank. A hopper pulling that output away takes the items but not the levels — those wait for the next hand that reaches in. So an automatic furnace costs nothing: a hopper on top for input, one into the side for fuel and one underneath for output makes it a machine you never touch.

Two specialized versions split the job. A blast furnace handles ores, raw metal and metal gear at double speed and a smoker does the same for food; both burn fuel twice as fast, so fuel per item is unchanged and time is all you buy. Neither touches anything outside its category, which is the blast furnace vs furnace answer: the plain Furnace smelts everything, and the specialists exist for the two things you do in bulk.