I have a odd tile liner in my heatform masonry chimney. The id of the tiles are 6" x 15". I am trying to install a vistaflame 1700 insert. My chimney is 12ft from the top of where the stove connection will be. I have decided to go with the oval duravent system. The problem is that the chimney doesn't come straight up. The first 3ft from the top is vertical and then it angles and offsets about 6" down to the smoke shelf. Because of this I can't use the ridged pipe all the way down to the flex that goes through the damper. I will have to run 5ft flex from the insert up to a short length of insulated ridged. From the short insulated ridged will be a 3ft flex that runs up to the final 4ft ridged pipe. My question is i don't imagine i could insulate the flex in the middle and get it down the chimney, so if my chimney tiles are in good shape, am I creating any problems?