How do I make a hopper output to two different hoppers?

I’m trying to get a two furnace auto-smelter in operation, but I can’t figure out how to do it using only one fuel chest and one chest for the smeltables. How can I make a hopper output to two directions at once?

A simple item filter should work. There are plenty of tutorials, this is the most popular –

A hopper cannot output to more than one direction. However, two hoppers can pull from the same double chest. So if your use a double-chest as each input, the hoppers should pull equally from that chest into each furnace.