Hi Dick,
I built a 40"Pompeii and used 3 sections of 8" flue. See:
http://www.fornobravo.com/forum/21/n...-a-2119-2.html (Neill's Pompeii #10)
I get absolutely no smoke out the front of the oven face as the vent and chimney draws exceptionally well.
I have just pushed them together and not even rivetted nor screwed them together and have had no problems what so ever.
I agree with RT and there is a science in setting a fire that produces the least amount of smoke. All dry wood, plenty of kindling to get that initial heat and no smoke. I made 2 stands that hold one end of the wood higher and allows the air to get in aqnd under the flames and works a trteat. Much quicker and hotter fires. I also found that you need to almost constantly tend the fire until you load the dry split logs or hard wood which wil take time to burn down to the coals which I then spread around the hearth. When almost ready to cook pizzas, I push the coals to the back and put 2 or 3 fresh aplit hardwood logs on which catch almost instantly, sweep the hearth and cook away.
Neill