I have a Hearthstone Heritage but I think this question would apply to any cat stove. I was told by the installer that the glue in cardboard might clog my catalytic combustor, so I should not burn cardboard. I have a new cardboard shredder, and I find that it is terrific for starting new fires. Am I damaging my cat? I use about a half to one cup. I use only cardboard with no ink or black ink.