I saw a few recommendations on this forum for the XR90. I had already been interested in it, so that was one of the things that encouraged me to buy it. I was hoping that some of the members on here could help out. Maybe hausdok can chime in, as he seems knowledgeable about this this model, and in general. First off, I understand the importance of proper venting. Which is why I'm asking the question upfront. In reviewing the instructions it specifies b-vent. Is this necessary or will a single wall 3 inch liner work? I ask because I already have a 3" liner in my "non-external" wall chimney. My chimney is capped at the top and the bottom and has a 3 inch (I assume single walled) liner. Will this setup work, or is it recommended that I replace the liner with a 3 inch b-vent? The rise is nearly straight up, will be approx. 20ft length. What I'm getting at is whether documentation just states b-vent, because in modern construction it is most common, but is it synonymous with a equivalent sized lined chimney? Your help is much appreciated, Mike