Auto Fuel is a mod for Valheim that makes fireplaces and smelters suck up fuel and ore from the ground and nearby containers.

If you want to make sure that your game is generating the resources you need, this is the best way to do it. With this mod, you can either

a) put coal, wood, or ore in a nearby container and the furnace and kiln should suck it up, or

b) drop coal, wood, or ore on the ground near kilns or smelters.

There are three configurable ranges:

The default range for each type of fueling is 5 meters.

You can adjust the config values by opening the in-game console (F5) and typing autofuel reset and pressing Enter.