Did my first chimney sweep today since we've had the Progress Hybrid. It is a 6" flex liner, 32', insulated. The previous non-EPA stove got me in the habit of cleaning the liner the first weekend of each month, and I'd get 3-4 cups worth of black, coarse creasote, with most of it coming from the top 2 feet. Today's cleaning yielded about a 1/4 cup of finer black powder. I bet if I had run the brush up and down again right after the last cleaning I would have collected almost the same amount. This is after feeding about 1.8 cords through the PH (full cords). Needless to say, I'm rather pleased, and if this becomes a trend I'll be stretching the time out between cleanings.