Factorio Forums

TL;DR - the order that furnace ingredient/fuel slot gets filled depends on what side fuel is on that belt relative to the furnace and when on "wrong" side, will first put an entire stack of that ingredient to fuel slot before starting to add them to ingredient slots. When the furnace is on the other side, it works as one would expect it to work.


I did a very basic test case with angel's petrochem/refining and creative mode and did this setup:
There I've opened the furnace to the right showing that it works as intended- add a bit of fuel to fuel slot and then to ingredient

A furnace on the other side of the belt looks like this: It keeps adding crushed coal, the ingredient of the recipe, to the fuel slot instead of recipe one.


I consider this to be a bug.
At the minimum, furnaces should have their slots filled in same order no matter how they're placed relative to the belts.
Second, if the ingredient is also a fuel source, inserters shouldn't end up adding an entire stack of it to the fuel slot.

Attached are is the game showing the problem and here is the mods folder (and save game, just because): https://drive.google.com/open?id=1PEm5h ... WtoIedzjQV

Thanks for the report however furnaces where never intended to work with items that are fuel.

You should be using an assembling machine if you want to process items with a fuel value into other items. Furnaces will always try to put anything with a fuel value into the fuel slot first.

Rseding91 wrote:Furnaces will always try to put anything with a fuel value into the fuel slot first.

Sure but the issue is that on one side of the belt, the fuel slot gets filled with a whole stack of fuel before anything is added to the ingredient slot while on the other side, only as much is added as in any normal furnace recipe.

hoho wrote:

Rseding91 wrote:Furnaces will always try to put anything with a fuel value into the fuel slot first.

Sure but the issue is that on one side of the belt, the fuel slot gets filled with a whole stack of fuel before anything is added to the ingredient slot while on the other side, only as much is added as in any normal furnace recipe.

Yes, because furnaces where never intended to smelt something with a fuel value: they *always* put fuel items into the fuel slot first. Because your fuel item also has a recipe the inserter grabs it thinking the furnace wants to smelt it but then the furnace puts the fuel into the fuel slot because that's where fuel goes.

I'd almost go as far as saying there should never be a furnace recipe that takes fuel items because it's unspecified if the item should go in the fuel slot(s) or the input slot(s).

Rseding91 wrote:I'd almost go as far as saying there should never be a furnace recipe that takes fuel items because it's unspecified if the item should go in the fuel slot(s) or the input slot(s).

How hard would it be to make it so that ingredient slots are always filled first instead of fuel ones? That would be a (seemingly) trivial change that'd make the whole thing consistent.

Of course, by "fill" I mean that only enough stuff would be added to the ingredient slot to craft a couple of recipes, not a whole stack. When that's satisfied, the items would start filling up fuel slot up to the limit that it usually takes.

hoho wrote:How hard would it be to make it so that ingredient slots are always filled first instead of fuel ones? That would be a (seemingly) trivial change that'd make the whole thing consistent.

But then what happens when you're trying to smelt iron? If it put the fuel in the ingredient slot first, then everything would get messed up.

You must use electric furnace in this case.

Or (if it works) burner with special fuel category, with burnt result output. viewtopic.php?f=47&t=55738

ManaUser wrote:

hoho wrote:How hard would it be to make it so that ingredient slots are always filled first instead of fuel ones? That would be a (seemingly) trivial change that'd make the whole thing consistent.

But then what happens when you're trying to smelt iron? If it put the fuel in the ingredient slot first, then everything would get messed up.

oh, right. I somehow managed to forget that furnaces auto-pick their recipe.

Oh, well. Guess this will stay as-is :\

The issue is with omnimatter mods. It replaces all ore with just omnite and that omnite gets turned to every other ore through various processes. As it also replaces coal, omnite also has burn value. The modder wants to add a new early(ish)-game recipe that'd use that omnite as an ingredient in a furnace but if that means that the fuel slot would end up with a whole stack of the ore before anything gets done, it'll not be exactly a good thing at the point in game where you don't really have ore to spare. I guess I'll suggest him the workarounds. What Darkfrei posted seems interesting