Help with Rocket Cob Oven Mod Design

Hi guys, newbie gathering materials for my first build.

Haven't got permission to do a thermal mass yet, so I'm heading down the rocket cob oven road, with a view to adding a thermal mass later.
Please have a look at the sketches and tell me what you think - still in R&D, no idea if it will work, need constructive criticism.
First Design is based entirely on Matt Walker's experimental oven, which seemed to work well. Since the fire goes right through the top of the barrel, there isn't as much an opportunity for re-burn as with a normal mass heater. He has an adjustable baffle which he can close off, redirecting exhaust through a bench.
I'm locating it partially undercover, and I want to minimise smoke as much as possible. Second design tries to make use of the barrel for re-burn, and sends exhaust down then back up into the back of the oven. The baffle is still there, but the idea is to start the burn as clean as possible, warming the oven as it goes, then open the barrel for serious pre-heating/cooking.

Tell me guys, will it start cleaner? Should I even bother with the mod? Does anyone know of a flue finishing under a pergola?

Shawn H. : Welcome To Permies.com and our sister site Richsoil.com, AND a Big Welcome to our Rocket; Wood Stoves; and Cob Forum Threads !

As long as you end up with a strong draft, you should have very close to zero smoke with all of these versions of a Rocket ! However exhausting
any where below the peak of your structure may cause you problems !

I am glad you found Matt Walkers designs, Yes you can certainly modify a barrel top to do exactly what're he did and it is one place to start From.

I am going to suggest starting just one step further back with your Rocket Core assembled and a Barrel over the top of the Heat Riser, pretty tame
and a common place to modify from !

-Am called away from computer will finish later ! Big AL

Shaun H. :So starting from the point where your core is complete, And you have placed your 55 gal drum over the top ( No Cutout in drum top ) -
The very next thing you must do is to instal a final vertical chimney ( When the Barrel goes on- the vertical chimney must go up )

The 1st thing that does is ensures you have enough draft, clean fire/ no burn back, and later when you are ready to experiment with your
horizontal run inside your thermal mass you already Know that the Rocket core is working and any problem you have is inside your thermal mass !

Many people ether use a pizza stone on the top of their barrel, or add 1.5 to 2 inches of dense Cob and then make an Aluminum foil tent from
several wide sheets of aluminum foil scrunched up and then shaped over a large bowl ( the bigger the better ) with the shinny side in !

The Aluminum foil can be reused again and again as your barrel top oven !

So - yes, you might try this before major modifications, but please do let us know how this works for you !

I am now going to look for a picture of a RMH brooder located under an open shed they successfully violated nearly every rule of final vertical chimney
installation and got away with it Your Milage May Vary Good luck Big AL !


Link below :

https://crosscutsandcastirons.wordpress.com/2015/06/10/mastodon-valley-farm-the-first-5-weeks/#more-963

You want the second picture labeled our shed and brooder, I am surprised that this '' Final vertical chimney '' worked for them !

On paper I can prove that you should always exit you chimney through the near center of the house, locating it about 3' - 5' above the peak of the roof
on the Lee or Downwind side of your structure ! Again Y.M.M.V. A. L.

Thanks Allen, you've been super helpful, and thank you for the warm welcome. I've decided to go with the tried and true design on the left, and save the RMH design for a separate system. It would have been nice to have it all-in-one, but that would place the oven and the exhaust right underneath the pergola, and as far as putting holes in the roof for a chimney, permission from my partner is the most expensive part of any of my projects, and that one just might cost me my balls. An oven next to the pergola has been granted, so me and my balls will work together on that!

BTW I also realised it was cavalier to post without reading the previous ones. I'm going through them now and learning a lot, including other rocket oven ideas.

Shaun H. : please note that I was trying to connect you with an earlier Tried and true version, one that predates Matt Walkers ! This was an attempt to give you
a common baseline, this model and the Matt Walker Variartion should perform well for you and give you bench mark to measure against ! Y.M.M.V.

When you make a NEW ? Original post or Forum Thread our computer scans for 'key words and phrases' and Posts a list of related or Similar threads at the
extreme bottom of this page/thread - Please remember to always give this area a check also ! Big AL