Big Al.
Thanks for the post. I appreciate it. I am excited to begin my journal with the rocket mass heater - I just want to do the best possible. I am going to look into getting Ianto Evans' great book 'Rocket Mass Heaters' ($15.oo U.S.) - thanks for the advice. I am also thinking about using insulated triple wall pipe for the heat riser, and maybe adding extra insulation around that to get the necessary diameter I'm looking for. Whatever I do, I will make sure to post it - along with the results, so others may benefit from my experiments!!
Thanks again Big Al - I truly appreciate it!!!
Tom K.