the second flue, thus making the existing problem more noticeable. B. TO TEST Cover unused flue at the top with a piece of cardboard and a weight. Start up a fairly hot fire... Sealing Chimney Dampers Click a picture for sizing options and prices Chimalator Damper / Cap Chimalator w/ Flue Extension Powder Coated Chimalators Round Chimalators 17+ Sizes to fit... almost any type flue opening... Plus Customs! The all stainless steel CHIM-A-LATOR easily mounts on top of a masonry fireplace flue and is operated by a convenient, adjustable...