This smelter is not like those 50 block monsters-pardon my exaggeration. All this needs is a bunch of iron and chests to get it going

Step 1: Getting Started

THIS STEP IS MANDATORY!!! DO NOT SKIP!!! You need to get 6 hoppers, 6 chests, and 2 furnaces.

Step 2: Setting Up

Place 2 furnaces with a two block gap in between, both at the same height.

Put 2 hoppers, facing each furnace in the 2 block gap(shift click on each)

Put 2 more hoppers on top of each furnace(once again shift clicking)

Put one double chest on top of the lower 2 hoppers, and single chests on top of the topmost hoppers

The topmost chests are for input and the double chest is for fuel input.

You are technically done, but if you continue, it makes things a little easier

Dig 3 blocks toward the furnace, digging the second block down one and the third down two.

Do the same on the other side.

Place a chest on the bottom-most block under the furnace, once again on both sides.

Place a hopper facing into the top of the chest by shift clicking on both sides.

Now... You are truly done!

To test, put something in for fuel and for smelting.

If you put ores/food in the fuel input, you will have to move it to the right chest-IT WILL GET STUCK IN THE HOPPER

This is the most basic form of this design. Feel free to modify it if you so wish.