I visited a friend today with a Buck 91 insert. I actually figured the stove hadn't been used since last spring when I showed them some basics (I'd previously never messed with a cat). Well, they've burned about a cord of very dry oak, hickory and ash left a couple years ago by the previous home owner. Problem is, the bypass around the cat was never closed and I'm told the cat gauge never exceeded 350 degrees! The glass was heavily creosoted up even though cleaned often. Today I did a proper light up (per manual) demonstration, closed the bypass and she went right up to over 1,000 degrees easily, so I assume the cat is happy. Question: With a cord of dry wood burned so far, beginner stove skills smoldering things and our current shoulder season, would you recommend another chimney sweeping? It was just done at the end of last spring's season. FYI, it wasn't that long ago I was on the steep part of my learning curve too.