cleaned out the chimney to the fireview.....it did not need it,but since i was up there..i sent the brush down..about a quarter cup of white powder came out...not even a spec of black soot..well may be a spec..but that was it...the chimney is brick, its external with an insulated liner..the hampton is used less and had about a coffee can and a half of black soot..and the chimney is a better set up...i do close the air all the way down,if i didn't that stove would use up all of my wood....there is a big difference in wood usage between the cat and the non cat..but the non cat can crank up the heat,when you need it,but at a cost.