RMH dimensions

Hi guys

I'm making a RMH to burn some waste wood in the garden.

I don't understand where exactly to measure for the 1:2:4 ratio.
Can someone share a diagram that makes it clear for me please?

I've got some 9 inch diameter ceramic chimney stacks which i intend to use.
Does this impact the height/length of the feed/tunnel/riser?

Will standard garden soil be ok to seal any holes? I don't expect it to be perfect. just functional and not too smokey.

Will the Rocket heater accept painted wood?

Thanks

M

Hi M;
It sounds like you want a simple J-Tube design rocket stove.
Although they can be built with many materials, preferably, you want your core to be built with solid clay bricks.
As you are just building an outdoor trash wood burner and not a mass heater there is plenty of leeway in build parameters.
Dirt is suitable to use in place of clay to fill holes.

The basic dimensions have one requirement.  They must keep the same diameter from the feed tube all the way through and up the riser. (chimney)
A Standard  8" rocket stove core has an 8"x8" feed tube that is most commonly made 16" deep.
The horizontal "Burn tunnel" has a "roof length of 10" -12" and is the exact diameter of the feed tube  8x8.
Your riser is also the same diameter 8" and it should be apx 3-4' tall.
If you have 9" material to use then keep it all 9" and you will have no problem.
Cracking is the biggest issue as the rapid heat changes stress most materials.
Solid clay brick will last the longest if true firebrick is not available.

With an open burner like this most anything will burn.
Yes, it will burn painted wood... if you or the neighbors do not mind.
Be very aware that nothing flammable is above your riser(chimney)  once lit and gotten up to working temperature, you can have flames showing.  

thomas rubino wrote:Hi M;
It sounds like you want a simple J-Tube design rocket stove.
Although they can be built with many materials, preferably, you want your core to be built with solid clay bricks.
As you are just building an outdoor trash wood burner and not a mass heater there is plenty of leeway in build parameters.
Dirt is suitable to use in place of clay to fill holes.

The basic dimensions have one requirement.  They must keep the same diameter from the feed tube all the way through and up the riser. (chimney)
A Standard  8" rocket stove core has an 8"x8" feed tube that is most commonly made 16" deep.
The horizontal "Burn tunnel" has a "roof length of 10" -12" and is the exact diameter of the feed tube  8x8.
Your riser is also the same diameter 8" and it should be apx 3-4' tall.
If you have 9" material to use then keep it all 9" and you will have no problem.
Cracking is the biggest issue as the rapid heat changes stress most materials.
Solid clay brick will last the longest if true firebrick is not available.

With an open burner like this most anything will burn.
Yes, it will burn painted wood... if you or the neighbors do not mind.
Be very aware that nothing flammable is above your riser(chimney)  once lit and gotten up to working temperature, you can have flames showing.  

Thanks for the reply buddy.

The ceramic chimney stacks that I have are shaped, so the diameter might be 8 inch in some parts and 10 inches in other sections. however, the top and bottom are 9 inch.

With respect to the length of the feed/tunnel/riser... where exactly do I measure for the 1:2:4 ratio?
Is there a diagram I can refer to?

Thanks

M

M Ahmed wrote:With respect to the length of the feed/tunnel/riser... where exactly do I measure for the 1:2:4 ratio?
Is there a diagram I can refer to?

This 1:2:4 ratio was what I used while optimizing a small J-tube, as long ago as 2011.  The measurement is done in the heart of the tube, seen in stream direction. 1 is measured from the top of the feed tube to the middle of the tunnel, 2  from the middle of the feed tube to the middle of the riser, 4 from the middle of the tunnel to the top.

At the time, I tried to establish a simple formula which describes the proportions of the J-tube. The idea was to come up with an acceptable way for measuring the thing. In my humble opinion, the formula should also contain the diameter of the tube itself. Something like 1/2:1:2:4, or 1:2:4:8. In the latter row, 1 is the tube involved, 2 is the feed depth as described, 4 the tunnel length and 8 the riser height. As a side note: for larger systems the riser could be shorter than the 8 times system size. Let's say 7.5 for 6" systems and 7 for 8" systems. This is just a guess, I didn't build a larger one than 4" and no testing has been done on larger systems as a consequence.

Lots of people wanted the tunnel to be longer and the riser shorter or something else, too much opposition and a lot of noise, so the whole of the proposal was ditched. A year later I was very busy with developing the batch box rocket so the J-tube formula was banned to the back burner.
But to my surprise, just now and then it creaps up again.

I have used these measurements very successfully.

I have successfully used proportions of 1:1.5:3, measured along the outside edges of an 8" system. 16" feed tube depth to floor, 24" burn tunnel length from end to end of floor, 45" riser from floor. This was a slightly shorter riser than planned due to special conditions. When the fire is roaring, flames seldom reach the top of the riser inside my bell; in an outdoor location without a container, the flames would likely move faster and come out the top, so a bit more height would be wise.

You mention using ceramic tiles for your J-tube. Unless they are special thermal shock resistant material, they will probably crack very quickly. Surrounding them with cob or even wetted packed dirt will most likely keep the pieces in place and functional.