Hello. Do you know of a brand of class A that uses a clamp/screw on ring to support the first piece of chimney in the ceiling box? I'm not sure if that is clear, but I thought I saw a ceiling box where the class A chimney could be extended below the ceiling box by the placement of a ring clamped and/or screwed to the first piece of chimney pipe. We are thinking that set-up might work in our situation but I can't find the site I had seen it on.