What’s the best way to close off an unused flue in a brick chimney?  A few things I’ve read suggest that capping it off can trap moisture and cause problems.  We are still using one of the flues for the woodstove, or I’d probably dismantle the whole thing.  We are re-doing our basement and I don’t want any issues with water leaking from the old clean out door.  It appears this has happened in the past, likely due to rain being blown past the current chimney cap.

One thought I had was to drop a length of rebar down the flue and fill it with concrete . . .