The forum has been very informative and I have been promoting it to others. This site will save peoples lives My situation: I have an 1800 sq. ft split level house. I removed my old EBI insert from Cambridge, Ontario ( no fan/heatilator ) 7" flue No direct connection from the flue to the chimney, creasote on the sides & top of the fireplace & smoke chamber to the chimney, missing sealant/rope on the windows producing gaps Wishing to upgrade: Current FP size is 36"w x 24"h x 22" deep with the rear FP wall at 25 " wide The FP floor is 1" lower than the brick lintal ( is that the right word to describe brick lip that sticks out of the front of the FP about 1 ft off the floor ?) Can I retrofit by cutting out the 7" flue & retrofitting with a 6" flue The chimney is lined with clay that is 6" x 10" on the inside My concern is that a 6" SS flex liner may fit into the 6" x 10" space with some "force" that could damage the liner by seperating the spirals creating cracks that could cause problems with leakage in the future. Or I could retrofit with 5" flue...this could be unwise because the volume of the hearth/combustion chamber would be choked causing smoke & insufficient venting? Do I REPLACE WIT A NEW INSERT ..if so ...can I REDUCE the 6" flue to a 5" SS flex liner if a 6" liner is too tight to fit into the 6" x 10" space. Thanks for your help.