Some what of a newbie we bought our house a little over 2 years ago. We definitely wanted a fireplace or wood stove and this one was here. I’ve been winging it learning through trial and error didn’t realize these things need a bit of understanding to operate it properly . It had no firebricks on the bottom once we replaced them last season it burned much better and much hotter. I didn’t know much about Cat until recently my husband took it out and cleaned it probably needs a replacement it’s an old stove. Made in the 80s so my search for a manual has not been successful. this knob closes a plate inside the fireplace I always a assumed that was to put the fire out but since reading the forums here I now realize this might be a bypass and should be closed all the way to push the smoke through the cat then out of the chimney?? Is this right ? I get nervous about shutting it all the way while the fire is going. the cat is behind this L shaped plate on the top close to holes on the door, which I also assume is the air coming from the air controls on the front of the door. Any help is appreciated!