I believe this is a cat at the back of the fireplace insert. I also have a couple of cast iron plates that overhang this, but they were not on there when I bought the house, and I have never used them. What am I supposed to do with this? Do I shut off the top damper once its hot and all the smoke will go through the cat? Do I need the extra plates? Also, anyone know what make this is? I heard its a heat-o-later or something. Thanks for any help, DeanB.