rocket stove mass heater using cob as pipe

hello and please forgive if this has been asked before, I didnt find it in my searches and browsing..
I have a few questions as I begin building my cob house and rocket stove,
First can I just have the exhaust from the rocket stove go into hollows molded into the cob couch or does there need to be actual pipe in the cob?
-I just read a reply to about the same question which states one reason to use pipe would be incase of  failure of the cob.
Second: I'm using a 55 gallon drum as the heater and I have 6 inch pipe for the burn tube, will this work ok or for a 55gal drum do I need to use 8 inch burn tube?
Third: I have been considering wrapping tin around the burn tube in a diameter that would leave about a 1" gap between it and the 55gal drum, capping the ends with cob and using fiberglass insulation as the insulation to keep the burn tube hot, will this work or melt down, or not be good for some other reason?
I live in a remote part of northern AZ with very good clay nearby, and I can find sandy soil but no real clean sand like you would get in the desert or buy, Im hoping that soil with the sand and straw will make good cob. So far Ive built a clay rocket stove using clay and sawdust and a cob wood fired oven using clay, sawdust and purchased sand. I love the feel of this stuff
Any advice would be appreciated,
Thanks

CriticalFactor wrote:
I have a few questions as I begin building my cob house and rocket stove,
First can I just have the exhaust from the rocket stove go into hollows molded into the cob couch or does there need to be actual pipe in the cob?

I have seen two things that may help.... First, when asked about the pipe rusting out or otherwise degrading, the answer was that the pipe served as a form to pack the cob around and once it was dry the pipe wasn't needed any more.... but it couldn't be removed without wrecking the cob either. Second, I have seen rocket stoves (not heaters) built out of cob parts with no pipe. Third... clay flue is clay with sand like cob and yet can handle chimney fires.

Second: I'm using a 55 gallon drum as the heater and I have 6 inch pipe for the burn tube, will this work ok or for a 55gal drum do I need to use 8 inch burn tube?

sounds ok.... rule one for anything you are not sure about.... try it in your back yard first.

Third: I have been considering wrapping tin around the burn tube in a diameter that would leave about a 1" gap between it and the 55gal drum, capping the ends with cob and using fiberglass insulation as the insulation to keep the burn tube hot, will this work or melt down, or not be good for some other reason?

Use rock wool (Roxul ?) as it handles the heat better. The gap is dependant on the CSA first. I think the barrel is 24in dia? the csa of the 6in riser is about 28 sqin. so that should be enough for that... however, the top part of the barrel is supposed to be hot, at least the top third. Having only an inch gap may cool that part of the barrel too fast. Also, the reason 6in riser is minimum is that smaller has too much surface friction, so even with a good CSA the small gap may give a similar problem. 2inches of insulation seems to be enough anyway (at least one person has used 1inch of Roxul and been ok)..... see rule one above.

Critical Factor : Did you get your questions answered? I have a few for you, with your experience, why have we not already heard from you !
The jobs that you have tackled will have prepared you to take in the additional information you will need to go ahead and create beautiful
houses for you and yours ! Have you been to cobcottage.com and rocketstoves.com, these are of course two sister sites where you can get
lots more information on building with Cob and information on Rocket Stoves.

I am still looking at a borrowed copy of 'the hand sculpted house'! Without hand on experience in anything else but building Rocket Stoves
(All three Types !) I would not consider building any thing else but maybe a Cob oven, West of the Mississippi Cob experience is unheard of and
talking about Adobe gets you tuned out !

Please Remember that every single person here puts their pants on one leg at a time. The experience you already have means you can ask
someone for clarification if you are hearing something that doesn't jib with your experience, The rest of us just have to follow along behind
because we haven't the experience to form an opinion !

For the Good of the Craft! Be safe, keep warm! PYRO Logical Big AL - As always,your questions/comments are encouraged and are Welcome!