Sealtight Chimney Damper Size:8 in. x 8 in. Once in place Once in place Even though Chimney Saver effectively stops water penetration The Sealtight Chimney Damper is also a great choice if you currently have a multi flue chimney cap or a stone slate chimney cap that does not extend very high above the top of the chimney Size Fits Flue Size 8" x 8" 6 3 4" to 9" Width x 6 3 4" to 9" Length 8" x 17" 6 1 4" to 8 3 4" Width x 14 1 2" to 16 3 4" Length 9" x 13" 6 1 2" to 10" Width x 9" to 12 3 4" Length 12" x 16" 9 1 4" to 11 3 4" Width x 13" to 15" Length 13" x 13" 10 1 8" to 12 3 4" Width x 10 1 8" to 12 3 4" Length 13" x 18" 9 5 8" to 12 3 4" Width x 15" to 17 1 2" Length 18" x 18" 15" to 17 3 4" Width x 15" to 17 3 4" Length