Can the secondary burn tubes in most stoves be removed without excessive violence to the stove? I wanted to remove mine so I could clean the chimney from the bottom, but it seems that they are held in by shallow metal boxes on both sides of the outside of the firebox, and those metal boxes are riveted to the firebox. I can't see any way to get them out short of drilling out the rivets, which I have no intention of doing. I guess I thought they were replaceable parts.