Just installed the nc 30 englander with double walled supervent chimney pipe. Large amount of black tar build up inside stove and in chimney and on glass within hours. Burning dry western cedar which Is at least 5 yrs old and probably 20 yrs old stored in wooden shed. Chimney is straight and outside temp is below freezing. Had the stove so hot that paint on exterior was smoking.The connection between stove and double walled pipe is not tight. There might be air leakage there though no smoke escapes. I guess the old cedar wood is too dry? I did have it outside in the summer and washed it and allowed it to soak in rain and then returned it to shed for several months to dry again. Darn squirrels pooped all over wood. I have a bunch of birch that was stored outside under a breathable tarp. Not sure if that will be better wood.