It can get very complicated. There are a few different reactions which occur in a Blast Furnace some are exothermic some are endothermic. BF is very simplistic

It can get very complicated. There are a few different reactions which occur in a Blast Furnace some are exothermic some are endothermic. BF is very simplistically a giant counter current reactor. Ore and Coke (the reactants) are added at the top at room temperature and hot gas (the "blast") is injected at the bottom and they flow past each other. CO is not the only reductant that plays a role Hydrogen primarily from the humidity contained within injected gas also plays a role in the heat balance of the furnace. Hydrogen is actually very efficient at reducing iron and avoids the CO2 byproduct. I know in the past some alternative ironmaking methods have looked into using things like hydrogen gas and natural gas (CH4) to directly reduce iron ore using a process abbreviated as DRI (Direct Reduced Iron) and for a while in the '90's this was marketed as a Blast Furnace alternative I haven't really kept up with technology. I started my career as a Metallurgist (Materials Engineer) working at a Blast Furnace they are hugely complicated beasts.