This is my second season burning, and last year I only ran the insert on the weekends. It's a late 80's Woodchief insert with a straight one story clay lined chimney(yes, I know I should S.S. line it. $$$) I was up on the roof to check the flue today and it was IMO pretty clean. The clay had a thin black film on it that rubbed off to clean tile if I rubbed it w/ a wet finger. So would brushing it do any good, or should I just check it monthly as i plan on burning more this season. I searched through 3 pages of chimney cleaning posts, and just figured I'd ask. I will probably pick up the necessary tools to sweep with next month. Thanks.