Each item takes one game tick to smelt, so a full stack of raw ore is done almost as soon as you load it in.
Unloading your trip
1. Come back to base with your raw ores, sand, cobblestone and any other items you want to smelt.
2. Open any furnace. A regular furnace works just as well as a blast furnace here, because the pack gives every cooking block the same speed.
3. Put fuel in the bottom slot and a full stack in the top slot.
4. Take the output out of the result slot right away. The stack finishes so quickly that you can move on to the next material almost at once.
Tips for big batches
- Keep the output slot clear. A furnace stops when its result slot is full, so take the results out often if you are pushing through several stacks.
- Mix your jobs freely. Every smeltable item cooks at the same speed, so it no longer matters whether you smelt ore, glass or stone first. Do them in whatever order suits you.
- One furnace is usually enough. You do not need a long row of furnaces to finish quickly. One furnace with fuel can handle a full inventory in a few moments.
- Watch your fuel. The furnace still needs fuel to run. Keep the fuel slot topped up so a big batch does not stall partway through.