Fire on other side of a wall (Maximum burn chamber lenth?)

Hey Folks!

Last year I built a greenhouse dryer for my small seaweed enterprise here on the Gaspe in Quebec.

I built a rocket stove as back up heat when its cloudy and/or raining.
The fire is made in a small lean-to annexe on the other side of a wall
so I do not bring in wood where my seaweed is being process.
This was a demand by the food inspectors.
And this is quite pratical, with the fans dust from wood would fly up and
cling to wet seaweed.
I allso covered the mass with ceramic tile so its food inspector proof.


In able to make the fire on the other side,
I had to make a longer burn chamber,
say +- 2 feet.
When the mass was hot,
the fire was good.
However when cold, I had some trouble with backdraws.

I wanted to know if someone had encountered similar problems with a longer burn chamber
or has info on this.

I will be rebuilting the feed and burn chamber soon, making it 4 1/2'' closser to the barrel.
In order to do this, I will have to make the wall seperating the greenhouse and lean-to with
perlite rich cob as the fire will be close.

I will be changing a few things as well.

1-longer stove pipe existing vertically
2-dryer wood this year
3-considering a small air intake at bottom of feeding tube with a 1'' steel tube 1'
(will this considerbly cool the mass after fire is out?) I use it mostly in spring and summer)

Thank you!


P.S.: If your curious about my enterprise and the seaweed harvesting process you can visit my website www.varechphareest.com (It's in French, but theirs photos and a
video if you click on Reportage in the menu)

Forget the down low air intake, this has proved to give more trouble than what it's Worth.

May be a simple trick would be in order. Raise your chimney, and increase your heat riser height. Have you respected the 1/2/4 proportions? Feed tube should be 1 unit of lengh, burn tunnel twice this size, and the heat riser should be at least 4 times the feed tube size.

Hello Stephane,
Your arrangement sounds quite interesting. By chance do you have a picture of the setup? I think that it would be important for us to understand the modified burn chamber and the situation driving that. I'll second skipping the secondary air intake to the bottom of the feed tube. It will encourage the feed tube to act more like its own chimney at the beginning and the end of the burn, when the heat pumping action is the weakest. Thank you for sharing your work on RMH's!
AL

Hello Stephane,
I just remembered a discussion of a stove that may be useful for you. Please check the following link: http://donkey32.proboards.com/thread/1023/accidental-discovery The user has a portable "Walker" stove and their heat riser had tipped over after a move. Not surprisingly, they found that the angled riser directed the heat to the location it was pointed at. The surprise comes from the finding that the stove appeared to burn just as happily this way as with the riser straight vertical.

A few experiments based on that finding could help you shorten the burn chamber closer to more "normal" dimensions. Which should help counter the backdraft issue and still get the heat directed to the other side of the wall. Good luck!

AL

Here are some pictures of the stove

And the chimeny

Off hand, I'd say smaller opening to the feed tube and make it taller. Also finish the chimney (to two-feet above any part of the roof or structure, etc, within a ten foot radius). And if possible increase the fire riser height, as has already been suggested.

I see possible problems with dimensions aside from the burn tunnel length. If you built it like the mockup, you have a feed tube that is 6 1/2" wide x 9" long, a burn tunnel that is 6 1/2" wide x 4 1/2" high, and a riser that starts at 7 1/2" square.

It has been reported that if a burn tunnel is not square in section, it should be taller rather than wider; wide and low does not work as well. You would probably do better to make it 7" high with a course of full firebrick (2 1/2" thick).

As mentioned, having the feed tube so much bigger than the burn tunnel makes more risk of smokeback or fire creep-up, as there will not be as fast a draft pulling the air and heat down as is needed. Better to make the feed tube the same 6 1/2" x 7".

Making the riser taller in proportion to the other parts, and raising the chimney, will probably help as well.

Stephane,

Erik and Glen said it all.

Low and wide burn tunnel is known for not working well.

And you realy need to raise your chimney above roof peak. And exit straight up too, the elbow pointing down doesn't help!

Thank you for all your replies!


Just to clarify, the burn tunnel is 6' 3/4'' wide by 5 3/4'' high. An extra 1 1/4" high from a brick thickness and 1/4'' to 1/2''
width from placing the top bricks a little bit to the inside.
Still to low in propor to width?

Here is my course of action:
1-Raising the chimeny making it exit vertically 2' higher then the top part of the dryer (thats easy!)
2-Remaking and shorthening the feed tube to the same dimension of burn tunnel.
3-Shortening the lenth of the burn tunnel.
4- Rock it up and see how it burns
If there is a problem, then I'll highten the burn tunnel to 7''.

5- Once it's working, cobing the wall with perlite rich mix.

I'll post photos once it's up and running.

Took years to report back but all your sugestings made it work properly!
thank you!

Pete Thomas wrote:Took years to report back but all your sugestings made it work properly!
thank you!

 Thank you for finding the old post and verifying the advice given by the rocket stove all-stars in here helped get it going properly!