How do I turn on Fast Smelt in my world?
Fast Smelt is a data pack, so it goes in the datapacks folder of the world you want to use it in. Load the world, or run /reload if it is already open. After that, every furnace, blast furnace, smoker and campfire in that world cooks at the new speed.
Minecraft says the data pack is incompatible, is it broken?
No. The game may show an incompatible warning when you load the pack, but it still works fine. Confirm the warning and continue into the world, then test it by smelting something.
How fast does Fast Smelt actually cook things?
Every smeltable item finishes in one game tick, so items come out of the output slot almost as soon as they go in.
Does it work on smokers, blast furnaces and campfires or just the normal furnace?
It works on all four: regular furnaces, blast furnaces, smokers and campfires. All of them use the same one-tick cook time.
Is there any point using a blast furnace or smoker anymore?
Not for speed. The pack makes the regular furnace exactly as fast as the blast furnace and smoker, so one furnace can handle both ores and food. The pack only changes cooking speed, so blast furnaces and smokers still accept only the items they normally accept.
Do some items still take longer to smelt than others?
No. Every smeltable item in the game cooks at exactly the same speed, whether it is ore, raw meat, sand or anything else that can be smelted.
Do I still need fuel in my furnaces?
Yes. Furnaces still need fuel to run, because the pack only describes changing how long items take to cook. Keep fuel stocked in the fuel slot as normal.
My hopper smelter isn't keeping up with the furnace, why?
The furnace now cooks faster than hoppers can move items, so the hoppers become the bottleneck. To clear a big haul faster, insert stacks into the furnace by hand. You can also split the load across several furnaces, each with its own hopper line.
Does everyone on my server need to install it?
Data packs run on the world or server side, so you only need to install it in the server's world. Players joining don't need their own copy.
What happens if I remove the data pack later?
Furnaces, blast furnaces, smokers and campfires go back to their normal cook times after you remove the pack and reload the world. Your blocks and items are not affected.