What does the group think on the topic of a minimum chimney height? I have been using twelve foot of prefab chimney for years and it works OK. I do sometimes wonder if a few more feet of chimney would increase the draft a bit. I don't get a lot of back puffing but it can be a little bit of a bother on a cold start. I see that some newer EPA stoves call for a minimum of 15 ft. of chimney - do I need to go higher?