Just my two cents....When I was running my 2550, my glass was never clean. It always had a dark coating on it, presumably creosote. But in all fairness, I burned the stove really low at 250 consistently. I didn't see flames unless it was to get the CAT up to temp. In fact, I didn't even know that these encores were capable of running with clean glass. The same goes for my Defiant 1945, except I run it at around 350 unless it's really cold then I crank it to 550. By the way, I have gotten incredible burn times from both of my VC's. The Defiant's stack is marginal but it must be ideal since it just went 16 hrs with plenty of coals left over to ignite rather large splits. The encore regularly got 10 hrs running at 200-250. Also, in my experience, these stoves aren't nearly as finicky as my new Oslo when it comes to wood moisture content. I can easily load 20%-25% splits without blinking into the VC's. However, the Oslo really wants 10%-15% or even lower to operate efficiently. Despite the VC reputation on these forums, that am sure isn't without merit, I feel these are great Cat stoves. The 1945 is completely controllable and the 2550 was after I tweaked the primary air intake by surrounding it with tin foil and magnets, essentially making the opening smaller. After I did that the stove was amazing. (I left the EPA holes open on both stoves).