well, since my chimney/2nd floor fire last year i've been revamping my wood boiler program---with a lot of help from the forum. weve been burning since just before thanksgiving. mostly at night (from 3p to midnight) and in the mornings, 5a until 10a. usually burn a heaped wheelbarrow (about 30 splits) from 4p until 930 the next morning----not bad i think to heat approx. 3200 sq. ft. with domestic hot water for family of 5. had a chimney sweep here on friday just to be cautious and check out mid-season conditions. he made two passes with the brush. 30 ft. of all fuel and the smoke pipe on the back of the boiler yielded about a coffee can of ultra fine very dark gray/black soot. no flakes, nothing shiny, no chunks. the soot was so fine it was like talc powder. some white/light gray ash was mixed in as well. around 1/8" of fine gray ashy buildup in the appliance and the topper was nice and clear, but black from soot. he came off the ladder and said keep up the good work.