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Any flaws in my Rocket Stove design?  RSS feed

 
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Ok so I have some 8'inch diameter pipe I am going to cut in half at a angle so I can simply put the two pieces together and then weld her shut resulting in a 90 degree angle as depicted

here with a lil' bit of a gap to get the point across..

I imagine this will be just as efficient if not more so than a 90 degree curve like this


I am going to make the gap where the heat rises out of the Jtube to the top of the barrel 3 inches for plenty of air flow the rest of the system will consist of used stovepipe no less than 8'in in diameter to keep the air flow going.

Since my 8 inch pipe is 1/4 thick I am not going to use firebrick I think that should prove to be plenty of insulation and will save $2.49 a brick for about 75$ worth in savings cheapest I could find around here few stores near me stock any, I am still going to use a much cheaper brick maybe broke up cinder blocks which I have a few of and some mason's sand and some clay.

my barrel length is 36 1/2 inches and my pipe is 8 inches at the bottom and you get 8+36 1/2= 44 1/2 for the length of the pipe going up into the barrel I have read that my ground pipe should be half the size of that so 22 1/4 can I make this 11 inches without any negative impact on heat/draw?

The barrel will have a detachable lid for easier cleaning I am also going to try and make little metal cleaning doors with hinges and a anchor for the door to stay put in the clay probably too much work but it'd be nice come cleaning time instead of taking a hammer to my clay to get access to it.



This drawing would be for the hot air leaving the barrel and heating the stove-pipes which I would then build a couch over.

I am thinking about for my feed area instead of just making it brick making it out of metal and have a metal drawer with a insulated knob that would slide out and sever as my ash catcher and I would like to have this 2 inches below my 8inch diameter start of the jtube. Also up near the top have a metal damper to open and close to allow for extra air in case my log is plugging the entrance or I feel the stove just isn't getting the right amount of air. Would this metal section get really hot or would the air cool it down enough where it wouldn't? Also it doesn't matter how deep I make my ash tray does it?

Also I'm thinking about extending the height of the vertical feed tube and putting a hinged door up top that I can close cutting off air from that area but keeping a well placed mid section damper near where the fire would be going to keep the fire going but eliminate any threat of a fire crawling out the top maybe put a few good drill holes in it to keep a little bit of draft going through to get rid of any nasty smoke buildup.
Ok I think that covers it wew I think i'll do a nice video of how I made mine just for good internet karma.











 
pollinator
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Jack have you been to rocketstoves.com to download a copy of the brand new edition of Rocket Mass Heaters? With this book in hand you will
know that you can come back here and share your plans using the same words to describe the shape size location and orientation of ALL OF your parts and
clearly understand the answers you are getting Big AL !
 
gardener
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The first flaw in your rocket stove design is using steel pipes for the burn tunnel (horizontal) and heat riser (vertical). These are the hottest parts of the system, and in a properly functioning rocket stove will reach temperatures near 2000 degrees F. in places. This heat combined with any free oxygen will quickly burn out or corrode even a 1/4" steel pipe. (People have reported failure in one or two heating seasons.) If you leave the pipe uninsulated, it will last much longer, at the cost of losing so much heat that it never reaches complete combustion temperatures and smokes and is inefficient.

The book, especially the latest edition, will give you a good understanding of the principles involved and why you need to follow the basic layout and construction methods.
 
allen lumley
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Jake : I tried to catch you while you were still online ! I have a horrible feeling that you have spent a little time over in U-tube LA_LA land !
Over there are hundreds of flaming units of death that people are posting videos of and 90% of them have one or more fatal flaws! These are
not true Rocket Mass Heaters !

In the olden days of nascar it was 'run what you brung', we all want to use the expertise that we already have and thats good and normal.
As a welder using metal for the Heat Riser seems like a no-brainer, however please take a moment and look up ''High Temperature Hydrogen-
-Attack ", simply stated steel even stainless steel will fail in the 2000+dF Working Temperatures of the Heat Riser !

Also the Heat Riser has to be insulated, after the rising hot exhaust gases hit the underside of the top of the barrel, they radiate off their heat
energy and cool, falling vertically down to the bottom of the barrel ! It is the difference in Temperatures between the hot rising exhaust gases
and the rapidly cooling and now denser exhaust gases that create the 'work energy' to push the exhaust gases 50' horizontally through the
Thermal Mass ! Without this temperature difference the gas flow will stall and your Rocket will start smoking !

Do you remember the movie 'Backdraft' a few years ago? Attempting to have a lid that closes tight over the top of the feed tube, will smother
a fire that has its combustion area glowing cherry red, any wood trapped within that space will continue to outgas its highly flammable wood
gases only needing the introduction of outside air to flash to flame, Two or three hours later your insulated combustion chamber is still above
the ignition temperatures of the combined fuel load ! Any one opening a lid over the feed tube to look in will be lucky to only lose ALL their hair,
including eyebrows!

By now you have a clearer understanding that a Rocket Mass Heater is not like a wood stove! Another difference is when the combustion chamber
cools the ''J- Bend' of your RMH'' acts just like the '' p-trap'' under your sink blocking any further air flow until you build your next fire ! Because of
this and the fact that the rocket mass heater needs to run wide open to burn at the extreme temperatures that give it its clean and highly efficient
Burn requires for safe operation NO Damper be used on a rocket mass heater RMH!

Paradoxically it is with a properly made insulated final vertical chimney that we guarantee that there is no fire creeping back up the feed tube, this
is one of the areas where it is similar to the wood stove, thought the exhaust gas temperatures inside the final vertical chimney are much lower
around 150dF

I want to strongly restate my wish that you buy and carefully read "The Book'' Rocket Mass Heaters, every thing you need to know to safely
build your own RMH is found in its pages, and if you have any problems you can come here and easily communicate your thoughts and questions
to myself or scores of other Fellow members 24 / 7 ! For the Good of the Craft !

Think like Fire, flow like Gas, don't be the marshmallow! As always, your comments and questions are solicited and welcome ! Big AL
 
Jack Pent
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hmm, ok i think I'll do without a lid for my feeder tube and I'll have to think over buying that book.. this ones just going to be a prototype to decide if i actually want to take out my wood stove in place for this.. not sure i am going to get used to havin to use smaller logs and feeding it a lot more.. if not it goes out to the shop!

..i'd still like to avoid using firebrick since i already have the pipe, could I use some 85% perlite 15% clay mixture to slather the inside of my pipe with about another quarterinch in thickness.. I'd like to try and keep it round since thats more efficient than square so ive read.. I'd also keep it smooth too if possible and thanks so much! sorry if its difficult to understand me...

 
allen lumley
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Jack Pent : While your sketch was a little hard to follow, most of us are used to answering these questions, and if we don't Think we understand -we will ask!

Even if this is Rocket Science -All the Science/Math you learned by the 4th grade. Mostly its the vocabulary that Ianto Evans who is a man of Welsh
Extraction, created to give us a common framework -within which to work. ( some times I think I can hear him Laughing !)

Good news on the 'Fire' Bricks, there have been literally 10s of thousands of early Rocket Mass Heaters made from old dead-soft housing bricks commonly
used in housing construction 100 years ago and easy to find for less than $1 apiece or free on Craigs list! Many of these Rockets were made 20 years ago
and still have their original bricks and Barrel !

I can recommend a second site that mostly deals with kilns for Pottery / Ceramics and so called earth /clay ovens like you get the best pizzas cooked in!

O. K. , please Goto : " www.traditionaloven.com ''

You are looking for the previous articles section where you will find articles on what is 'fire clay' and articles on fire bricks and Alternatives to fire bricks

As the article explains -there are two types of 'Fire brick' 1) soft and light 2) Hard and dense And each has a separate purpose- I am telling you now
that we generally prefer the dense fire buck weighing 8 lbs +- !

The old, dead-soft, red, clay bricks (you can use them like sidewalk chalk and they leave a well defined mark behind themselves ) fall nicely between the
two extremes in 'fire brick'

Unfortunately the ratio you chose will not make a good 'snow ball' it will just not hold together in your hand. By time time you have used enough Clay to
Perlight to end up with a rigid enough structure that can last even one heating season, we lose some of the insulate qualities of the perlite and need between
2'' and 3'' thickness

Have you seen the large diameter tubes of heavy cardboard usually called Sonotubes that are used as forms to make in-ground supporting piers for
general construction ? you can easily use a 8'' Sonotube as the inside form of your Heat Riser, and regular stovepipe for the outside wall of your Heat Riser,
The Sonotube will burn up burn out during the 1st few initial firing of your future rocket mass heater RMH!

One more thing, We try hard to listen to every single new idea -as that is the only way we will ever grow and improve ! In spite of that we can fall into the
habit of ''this is the way we have always done it''! If you do not like or understand an answer you get here always feel free to ask for a second opinion !
For the Good of the Craft!

Think like Fire! Flow like a Gas! don't be the Marshmallow! As always, your comments and questions are solicited and Welcome Big AL
 
Jack Pent
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Quote: ''we lose some of the insulate qualities of the perlite and need between
2'' and 3'' thickness''

I'm not looking to insulate the pipe but keep oxygen out away from the steel so it can't rust and just let the pipe itself be the insulation

Nice sonotube idea
 
Glenn Herbert
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Steel pipe has no practical insulating quality for the purposes of the RMH - it is quite a good conductor and will pull heat away from the interior. A quarter inch of refractory material is nowhere near enough to hold together either. You need at least an inch, and two or three inches is the recommended thickness for durability. Spending the modest amount on the book will save the cost of a batch of brick or other material for a first wild experiment, not to mention the wasted time. It is often repeated here, do a setup by the book first, then you can experiment on your own and see whether your trials make for improvement.
 
allen lumley
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Jack P. : A quick look at '' The Engineers Toolbox.com '' for the specific heat of selected materials and the ability of a material to transfer heat (though itself)
will quickly show you that if Air has a heat transfer value of 1 all of the insulating materials are clustered at one end of the scale, and Metals and
most rocks are clustered at the other end. Steel can not be considered insulating just by being thick ! Big AL
 
Jack Pent
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https://www.youtube.com/watch?v=YxFHBxHGPkg

Here's my near completed functioning rocket stove
 
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allen lumley
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Jack Pent : Great welding skills ! It is now obvious why you have chosen the route you have taken! In Nascar circles they used to say ''Run what you Brung! ''

There is lots of room for you to show off your skills here at Permies.com.

It is a Truism that we all learn more from the negative experiences in our lives than we do when everything goes perfectly to plan! As it stands now we have
failed you. I hope that we will be able to use this event as a good way to actually talk with our newest members, instead of talking at them, We want you to be
part of the team that greets new members to these forums and says yes you can! There is still much much more we All can learn from your build !

''Max'', Has shown you the path Rob T. has taken to highlight what he learned from the early failure of the Heat Riser part of his Build. I hope that you too can
follow His lead as another valued Fellow Member and share with us your ongoing experiences with Your Rocket Build, It can have a marked positive effect where
we have Failed to be convincing with our rather long winded and overly Technical Thread Extensions.

For the Good of the craft ! Big Al !
 
Jack Pent
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Thanks a lot allen and nice video Satamax once my steel pipe gets eaten up I think i'll try and copy your idea that was nice work with the firebrick and the steel frame.. I think I got quite a few years to go though and yeah.. I just wanted to show people how I did it and what I did I know its not the best video and that my words are a little loopy but I imagine some folks might benefit from it the only real issue has been that I spaced the grate too far apart at a 1/2 inch and it allows the coals to fall through so if the ashbox is empty its difficult to get a fire going so I am going to weld some more rebar on that bad boy to make it a quarter inch gap, and my clean out door has a gap that I had put BBQ gasket around but it still melted.. so that works against my suction down the feed tube a little bit but other than that when the smoke turns to steam boy howdy I am a warm puppy.
 
Glenn Herbert
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Your stove as you show it would probably last for several years, because it will never get hot enough to burn properly and be efficient. As long as you are using the heavy steel for the whole combustion zone, it will conduct heat away from the fire. At least an inch, preferable 2 inches, of perlite/clay around the whole feed tube, burn tunnel and heat riser should let it get to proper temperatures. Keep an eye on it after that, especially the area where the burn tunnel and heat riser meet, as that seems to be the first failure area for these metal J-tubes. It will probably fail during a really cold spell when you are pushing it hard; hopefully it will not fail catastrophically but just lose effectiveness gradually. Satamax posted about a heavy steel pipe core that failed within fourteen burns.
 
Jack Pent
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The stove does get hot enough to burn properly meaning ~no smoke and from my pictures attached you can see that the steel I've used has held up nicely so far and it's been in nightly use as its been below 32 degrees nightly during this winter we've been getting here in Arkansas I like it especially because it's easy to control if I want it to be a 'rocket stove' (3x the heat) level where its glowing a dull red ( I don't like it to be a bright orange but have gotten it that high!!) I just fill her up until the coals are nice and hot and fill it up horizontally and vertically with wood and it'll switch to the rocket stove mode if I want to be at normal stove heat I just throw in a few sticks horizontally. Generally I get it up to rocket stove heat an hour or two before I go off to bed and the heat from the heatmass really coasts well until around 4am I go to sleep at around 10.

Here's the pictures to prove it first one's the horizontal glowing a dull red second one's the inside of the horizontal and I must say I love my ashbox and cleanout door- no way would I have been happy with vacuuming the ash





One thing I'd like to change would be a slight angle to help the smoke go the right way, and have a 45 welded onto the 90 at the feed bin to allow logs to slide in horizontally much easier but besides the smoky start-ups the stove has been much superior to our old Blaze King.. might as well use that thing as a refrigerator now..
 
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