Thanks for the replies. Here is a little background on our stove. I wanted a large unit as we have a very old story and a half house. The spot we chose for the stove, only
allowed for a 6' bench. I decided on an 8" unit. We put 3/4" ply on the floor and covered with tin foil, then a layer of common brick. Then a leveling layer of cob, followed by
a layer of fire brick in the stove area. We have a J tube design, all out of fire brick. I rolled some 10 ga. steel for our heat riser exterior and used perlite between the brick
heat riser and the steel. (18" dia.)and capped it with some perlite cob. I then rolled some 10 ga. for the outer barrel (I didn't want to use a gas barrel) it is 24" diameter.
I built the manifold out of brick and used 8" diameter ducting, down and back in the bench and put in a water trap as the ducting goes vertical. Our bench is not finished yet
but the ducting will be totally encased in cob.
We have so much fall work to do that we won't get to finishing the stove until later but it works so well that I had to write in. I'm not sure how accurate my cheap electronic temp gauge is but it is showing about 600 degrees F on top the stove, about 400F at the bottom of the outer barrel and 200 F on the ducting as it goes vertical. I wish I had more room for more bench length as it appears to me, I am wasting some heat.
I've attached a few pictures.