Dataman,Good Stove Then. Good Air Supply is key I found out. In with the good air, out with the bad. Only time mine burned dirty (black) was when chimmney was blocked. I keep metal fabic in chimney part going thru wall to stop birds. Left it in. Worked until it got clogged. Removed that and I was golden. Also holding open OAK flapper worked too (magnet). But real problem was stove could not breath. Been good stove. On 3rd Season. Pellets delivery other day. Test burn last week was flawless.