EDIT: Probably wrong, probably intended game mechanic, but I didn't see the Cooling button.
BUG?
I have 1 worker in the Mine (ok)
I have 1 worker in the Smelting (not ok), it complains about "1 worker idle - buy more furnace" (I have 1 furnace, the starting one),
BUG: When I try to Smelt an iron ingot, I use the bellows to get it up to temperature, but even after stopping, the temperature raises & I have no way of cooling it down (WRONG, I found the "cool" button), not even when the coal ran out the temperature still was climbing.