I installed my wood stove 9 years ago with parts purchased from a local chimney sweep. Today I had them come to inspect it and he showed me damage inside of it from one or more chimney fires. So I'm going to have to replace it. I'm not sure what a good brand of triple wall pipe is and also, where the best place (online) would be to buy it to save money? I was hoping some here might have some idea. The chimney is 18' tall and 6" around. Thank you!