New guy needing Rocket stove advise

My ultimate goal is to build a rocket mass heater. I have purchased and read the Book "Rocket Mass Heaters" by Ianto and Leslie

I decided to build a rocket stove first (which i Have ) to verify it works before I build the Mass heater

The rocket stove works but not as good as I thought it would. I built a J Tube out of 6 inch square tubing 3/8 inch wall

Feed tube is 13 Inches deep total
Burn chamber is also 13 inches long total and is raised 2 inches up from the bottom of the feed tube to keep hot coals at the bottom of the feed tube.
Riser is 34 inches tall.

5.25 opening all the way start to finish

Not much of a rocket sound. it draws but fire trys to climb up the wood in feed tube.

I would appreciate any help from you guys that already made this work.

First off, steel is not the best material for a rocket. It will conduct heat away from the burn zone, cooling it and weakening the effect. Do you have any insulation around the steel? I think even fiberglass wrapped around it would help for a short-term demo model.

Kim Woodson : Welcome to Permies.com, our sister site , and A Big Welcome to the Rocket and Wood Stoves
Forum/threads.

There are historical reasons why the Rocket Stove gets short shift from Evans' and Jackson and the core of his followers,
that being said It is understandable that you have called your creation a Rocket stove, it is not. More accurately it should
be called a Mass-less Rocket Heater! The Conventional Rocket Stove combines the A horizontal Feed Tube and Burn
Tunnel.

There is an old saying that fits your situation perfectly, " To a man with a Hammer all problems are nails!'' As you had
the skill set and the equipment and supplies to attempt to build Your unit out of steel it must have been a natural idea to
proceed to create a unit that way! With a little sleuthing I believe we can help your grasp the basics of RMH Plumbing,
and find a better build !

Unfortunately, I have to tell you that At the high working temperatures of a properly made RMH all iron and steel will
fail do to High Temperature Hydrogen Attack , also called hydrogen embrittlement or steam embrittlement !

I have no problems visualizing how you made up the ends of your two pipes where you butted the end of the Heat Riser
to the end of the Burn Tunnel where you made a so-called 45 degree cut and 'but welded' the two ends into one unit.

With an inside Cross-Sectional Area of 5.25'' Xs 5.25'', or 27.56 sq. in. we should closely examine how the other 90
degree was shaped and the orientation of the Feed Tube and Burn Tunnel.

To find the correct ratios of Depth of Feed Tube, to Length of Burn Tunnel, to Height of the Heat Riser we generally say
1 : 2 : 4, with very specific measuring points. Starting off with the depth of the Feed Tube we subtract the depth of the
ash/embers pit from the Feed tube 13''-2''=11'', then we find 1/2 of the height of the Burn tunnel 5.25''/2=2.6'' and are
down to 8.4'' . then if we take 1/2 the height of the Burn Tunnel from the height of the Heat Riser,34''-2.6''=31.4''.
using these measurements the Heat Riser should be 4 Xs 8.4'', or 33.6'', so you were very close, in this case the Height
given for the Heat riser is a minimum height !

The 13'' for the length of the Burn Tunnel gets trimmed by the 5.25'' = 7.75'' this is short for the burn tunnel but here
the correct length of 8.4''+8.4''= 16.8'' is a maximum length ! something in the 14''-16.5'' is acceptable !

I would like to see a picture or a sketch of the Area where the Feed Tube and the Burn Tunnel but against each other !

In part your problem with smoke back gets worse after the combustion system gets hot, at that point the Hot metal
helps to turn the Feed Tube into a second chimney, as the effect of the Heat Riser is not strong enough !

You can cut the Present Feed Tube off of your unit and create a true Rocket Stove, and insulate around the horizontal
feed tube and riser and it will function as a pretty efficient out door cook stove for a long time before it fails !

At the bottom of this page find where it says permies >> forums >> Energy >> rocket stoves click on Forums

On the Forum page scroll down to Permies. com, , then down to tinkering with this site click on Tinkering

Then find and click on How permies.com Works - links to useful threads ! From their you are on your own, but try
to send a sketch or a photo of the Feed tube, Burn tunnel ! For the Good of the Craft ! Big AL

Thanks guys for the reply. I understand that Mild steel is not going to work. I was just interested in getting my lengths right before
i went to the trouble of building the RMH to find that my burn tube is to long/short or what ever. Today I built my first fire in it and at the top of the riser temp only got to 340 deg F. i
then took 1.5 inches Mineral Wool and wrapped the riser only and it brought it up to 550 deg. I still consider that a failure. I guess I bought the wrong book. i see lots of designs on here but I did not see dimensions.

So is 1 foot feed tube, 2 foot burn chamber, and 4 foot riser what I should work towards?

Thanks,
Kim

Big Al,

for some reason Only half your post displayed on my computer. I am reading your reply now. Thank you so much for the dimensions.


Kim

Kim Woodson : yes i know! sending a p.m.

UPDATE:

I cut off the feed chamber and added 2 more inches to the burn chamber making it 15 inches now it draws much better. I guess I proved to myself that this will work so on to the RMH.

My question is now when I build the RMH I will have to have the Feed chamber so what measurements do I use for the Real RMH? I have a Larger underground concrete garage so space is not a problem with an existing 12 inch hole thro the roof 12 ft from the floor.

You say "underground garage". Is the garage what you want to heat? Will you be spending a lot of time in it? A J-tube RMH requires regular attention while it is burning, and if you will not be in the garage the whole time of the burn, it will become a chore to keep up with it. If you want or need to have the RMH remote from your normal daily location, you would be better off with a batch box RMH instead of the J-tube style. Peter Berg has developed the batch box to high efficiency with minimal attention - look for his threads on the subject.

https://permies.com/t/40007/rocket-stoves/Results-batch-box-thingy-Innovators

Kim Woodson : We have not talked about your location, climate, the fact that the RMH is a space heater that you want to retro-fit into an
existing site, or the use you have for the site or its size ! Of more than a little importance is the layout of the rest of the structure and
number of floors ! Please try to send pictures or more than one sketch, close to scale is preferred.

The only reason I can think of for a 1 foot hole in the roof is the presence of an insulated stove pipe passing through that spot. if so what
is its inside diameter too?

For the Good of the Craft! Big AL