there is cast iron in there. It's just hollow. If you just glance at the heat riser you will see it isn't really a tight seal. My question is how did it run if the heat riser was stuck in the "heat" position? Did it run OK? I jammed mine in the "heat" position (although at the time I had no idea which position was heat or otherwise)I thought I was going to explode something, it popped and lurched horribly.
