perhaps it would be better/easier to just get a burnable amount like the vanilla furnace does?

This issue was just to save the request from the forum. How we solve this is our thing.

fair enough, but it's still a question what would be preferable, vanilla furnace option is easier and gives user a lot more ability but is there something about the furnace (lore wise for lack of a better term) that merits it should be coals only?

well the zeppelins are coal only atm. some user requested wood too. But I think it would be better just to use coal

well stealing vanilla furnace code is just doing TileEntityFurnace.getItemBurnTime(cart.getStackInSlot(SLOT)
which returns an int value.
thats why i ask, should we use vanilla or is there a lore-esk reason to use just coal.