Please consider making structures that take fuel, such as smelter, stack furnace, kilns, ovens, etc. to rather (or also) have an accessible fuel inventory window where fuel can be manipulated, at least until lit or while not burning. This, so that you are not locked in with whatever fuel, for quality, quantity or whatever other reason you have added, such as wanting to remove a shitty piece of coal, etc.
(Sure you can argue skill issue, but don't, this is clearly an objectively superior system)