Minecraft wiki entry for Hopper, associated text: To make the smelting process more efficient, it is possible to use hoppers to ensure a furnace is never left empty. In the shown schematic, chest A is for items such as uncooked meat, chest B is for fuel such as coal, and chest C holds the output. Since furnaces can hold fuel without a chest, chest B and its hopper are unnecessary. This type of system also works with the smoker and blast furnace.