[Cob] Rocket Stove

[Bernhard Masterson]

Hi Chris,

One of the misconceptions of rocket stoves is that they do not need conventional chimneys.  I have built quite a few very successful rocket stoves and have tried several alternatives to a conventional chimney.  Some work okay but none seem to work as well as stoves with vertical terminations, especially stoves in windy locations.  By conventional chimney I mean a vertical stack at the end of the ducting run that terminates 2 ft. above the highest roof point with in 12 ft.  This is to allow the exit gasses to vent into a neutral pressure area when winds blow and it does indeed provide a little additional draw and improve the burn and stops back drafting.  Please see the section I wrote in the back of the rocket stove book for more information on this to help your situation.  Even though the final flue temps are often between 100 deg.and 200 deg. there is still enough stack effect to create additional draw and make the effort of a vertical stack worthwhile. IMO.  Best senario is to have the vertical stack in the conditioned space.  If it is exterior then insulating the stack is necessary. 

- Bernhard 



Get under a sustainable lifestyle umbrella, the carbon is going to hit the fan.

____________________________________http://bernhardmasterson.com

Natural building instruction and consultation

From: Christopher Reinhart <sandymud at gmail.com>
Cc: coblist at deatech.com
Subject: Re: [Cob] Rocket Stove
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from Phil:
 
...we had a lot of problems getting its drafting the right
> direction.
>
> Do you have a primer hole near the base of the vertical exit flue? When
the entire system is cold, placing a burning piece of newspaper into this
hole has always helped me get things moving in the right direction. This is
described well in Ianto and Leslie's book.
 
A rocket stove should not need a "upward" stack at the end to draw like a
> standard wood stove.
>
 
Correct. Adding more height to the exit pipe will not increase draw. Adding
more height to the chimney contained inside the barrel will.
 
 
> My question. Now that its fired up to keep the greenhouse above 40 degrees
> are there any issues with adding new cob to the old dried cob?
>
> There may be some cracking, but if you outer layer of the old cob several
times and allow this to penetrate, it may not be as bad. Depending on how
you plan to finish the cob, the cracks won't be a big deal. When I have
gotten cracks, I just wait until everything is completely dry, mix up some
very smooth cob, and run it into all the cracks like caulk.
 
 
> If I add a permanent "stack" to the exit of the rocket stove outside the
> greenhouse that is 4 ft high and capped should there be any issues?
>
 
There is a limit to how long the exit run can be on a rocket. I've never
built one longer than about 25', but the literature and various posts here
have talked of longer runs. What type of issues are you worried about?
 
 
> The exit end of the rocket stove where it leaves the greenhouse is about 14
> inches above ground (solid clay) but is susceptible to damp from
> condensation on walls and rain seepage. any thoughts on keeping it totally
> dry?
>
 
A link to a photograph or a sketch of your situation would help answer this
question. Off hand, though, I think that "keeping it totally dry" might not
be essential for your greenhouse application.
 
Hope this helps.
-Chris Reinhart