The Large Furnace, an outdoor player-deployable smelting tool in Rust, is the late-game version of the smaller furnace. It and the smaller version acts as one of the first item hurdles that players aim to overcome on wipe day due to their Low-Grade Fuel requirement.
The large furnace is used (along with Wood) in the smelting of High-Quality Metal Ore, Metal Ore, and Sulfur Ore to convert them to their refined forms. Players may deploy them on the ground on relatively flat surfaces, given they have proper Tool Cupboard authorization. Large furnaces cannot be placed underneath a standard roof/floor unless you build up roughly three stories high, making it quite tricky to wall them in.
There are methods using Floor and Triangular Floor Grills, which can be placed above large furnaces, but this comes at the cost of their blueprints and base defense. Aside from their smelting utility, they also have a general-purpose storage capacity of 18, sometimes playing the role of a box when nothing is ready to be cooked. Their chief utility remains using less wood per ore smelted.
Large furnaces do not give off heat or comfort, unlike their regular furnace counterparts. Large furnaces are obtained through drops in mid-to-high-tier crates, as well as from scientists. Players may also purchase them directly from Outpost for 350 Scrap or invest considerable scrap and learn them via the tier 2 workbench tech tree. You cannot cook food in them, no matter how many times I’ve tried.