Rocket Stoves

thomas rubino wrote:Very Cool Peter!
Besides being functional it is a work of art!  

Congrats on version #5!
Is there a version #6 floating about your head?

Hello Thomas and fellow Permies enthusiasts!  

Greetings from the Canadian PNW. We are currently enduring a 10 day run of cold liquid sunshine that has us trying to avoid early sunsets and soggy outerwear during our winter solstice!  

Yes and Thank you! Yes! There will be a Frankenstove Mark 6!!! Soon to be built and this time it will be documented online in a step by step series from the “ground up” so to speak…… it will take every thing I have learned from the “Frankenstove Franchise featuring what I have done wrong on previous builds and how they got resolved in “Frankenstove Mark 6”
However, Frankenstove 6 will be a unique build for a 8’ x 12’ greenhouse over an aquaponic fish pond for growing lettuce and other greens year around!!! Yes! Another ambitious project that I wish to share!
This will include a sizable increase of thermal mass to help regulate the temperature during late fall to early spring. It will be wood pellet fueled as all other Frankenstoves and be of a 3-4 inch ceramic tube riser. You will have to follow along for other modifications that may be interesting for those that may wish to build their own. I hope to keep tooling down to a drill, a grinder and a flux core welder to keep the build feasible with respect to fabrication cost. I also promise to pull out one of my older builds to “recycle and reincarnate them” keeping the spirit of continuous improvement with Frankenstove modifications like its iconic movie namesake!  
It’s good to be back on forum! Stay tuned!

Hello Peter,
I'm writing for just one reason: I want a small rmh for a small space - about 300 square feet. Whenever I look at rmh designs, they are gigantic. Yours is small. Maybe you or someone here can advise me: can I build a small rmh? Do you know? (I'd rather not be as high-tech as your designs, if possible.)

Shodo,

In theory you could build 100mm/4" BBR system. The ISA for such a heater would be around 2.4 m2, so the heater could be 30x30x55". However the small systems, with riser diameter less than 5" may not always work as desired. They are more demanding in workmanship and material selection.

Thankss, Cristobal. It's  a start. I probably shouldn't do the "more demanding" version, but 30" is very small so I can go a little bigger.  

Cristobal Cristo wrote:Shodo,

In theory you could build 100mm/4" BBR system. The ISA for such a heater would be around 2.4 m2, so the heater could be 30x30x55". However the small systems, with riser diameter less than 5" may not always work as desired. They are more demanding in workmanship and material selection.

Hello Fellow Permies!

A long time ago in the Frankenstove Vertical RMH franchise, I promised the forum that I would perform an "Autopsy of the Frankenstove 2" In true Canadian fashion, I apologize for the extreme wait. With Frankenstove 6 on the drawing board to heat an aquaponics greenhouse, I feel that it is important to visit the "teardown - destructive " take apart of Frankenstove to make F6 (Frankenstove 6)  benchmark build so many of you interested in building your own have some guidance of building my version of these amazing stoves.
I am trying to attach photos so you can see how the intense heat affected "F2" but it seems my tech savvy is not letting that happen. So, I will explain in text.
Here is what I noticed in the teardown,
1) The refractory material recipe worked perfectly and held up to the heat without issue.  It cured to a solid, difficult to dig out of the metal housing. This is encouraging as there is the possibility to make a solid core riser without having to use the factory made ceramic tubes if you choose.  I have some spare 4" diameter ceramic cores so F6 will utilize them in the new build
2) The metal internals were severely damaged due to extreme heat stress and thermal cycling basically destroyed the metal riser causing a crack where the weld was on the pipe. F6 will redesign the horizontal burn tube to host a 4" ceramic tube and avoid as much metal in the burn zone as possible. This will include the redesign of the Wood Pellet Feed System and corresponding pellet ash retrieval system.
3) The bell  was relatively clean and very little fly ash was in it after years of use. F6 will be designed where the bell housing will be removeable for inspection.
4) The cast iron pan used as a deflection wall to direct the flames up the riser had a 3"hole where the combustion flame met it and fortunately the refractory held up with little to no damage. Obviously, once again the thought of using any type of metal in the riser / combustion area is not a great idea and will, in time will fail and need reworking.

Again, my apologies for not being able to post any pics

Thanks!

Hello Fellow Permies!  
Here are the photos of the Frankenstove Mark 2 Autopsy I recently performed as promised... Finally figured out the picture attachment issue!  Yay!

The first photo shows the retired Frankenstove Mark 2. I did some work on the pellet feed and it proved I needed a larger opening for higher output temperatures.
Photo 2 shows all the parts that were in the refractory matrix
Photo 3 shows the split of the Vertical RMH where the horizontal burn chamber meets the vertical metal riser insulated with refractory.
Photo 4 shows an attempt to dig thru the refractory material which had the consistency of concrete!
Photo 5 shows the blast damage from the horizontal flame meets the 90* transition to the vertical riser! The intense heat burned a hole right thru the cast iron pan! Fortunately the refractory poured behind the pan and maintained the integrity of the heat shield to divert the flame vertically!
Now that you can see what I am talking about, you can see that metal has no place in the vertical riser in the world of RMHs! The extremely high temperatures cause severe spalling of the metal to failure and causing a major inconvenience to replace the "innards" of your stove.
I really hope that any newbie comes across this thread will research better riser materials in their build seeing proof that metal risers are a bad idea.
The Frankenstove Mark 2 lasted a few years heating a 2000 square foot home using wood pellets without issues; other than burning out pellet baskets. So, I still struggling to build the ultimate pellet basket that works without burning itself up.  The Frankenstove Mark 5 has improved on this issue and the lessons learned will be relayed to the development of the Frankenstove 6, which will be built to heat an aquaponic greenhouse.
Stay tuned as Frankenstove 6 is under design build and I am optimistic to share the build with all y'all.
peace health and happiness!
Peter Chauffeur

Yes some good informative photos that might well help future builders.

Hello Fellow Permies!  Great News up here in the Canadian PNW!  

“Frankenstove 6” has begun fabrication. I have been given the Grace of my Wonderful Wife Patti to shift some of the items on the Home Job List and I will be posting the progress of the build as I go!  I will try to keep the construction simple by using basic tools such as a drill, grinder, welder and hand tools. This project will use extensive welding to create a Vertical Thermal Mass Rocket Stove that will be used in an 8’x12’ greenhouse that is built over a 8’ diameter aquaponic pond to grow food like lettuce kale and arugula.
The main materials will be one 100 lb propane cylinder, one 30 pound cylinder, some square tubing, ceramic tubing and refractory cement and an aluminum toolbox! Yes! This will have the general look of the F5, but much more compact to fit in the greenhouse. Of course, it will be wood pellet fed and of course, not require any electricity to operate. I know my design strays wildly from the grassroots style of rocket mass heaters on this sight but it’s design may inspire others to push the envelope when the decide to build ther own!  I should also like to continue with the 4” diameter riser that has operated in Frankenstove Models 3, 4, and our current operational Frankenstove 5. So without further ado, here are some pictures of the start of the build. Stay tuned, be safe, be warm, be Kind!

Hello Fellow Permies from the Canadian Pacific North West!

GREAT NEWS! Frankenstove Mark VI development reached another fabrication step and I would like to share it with you!  The main body has taken shape as I have massed the materials necessary to safely build on a shoestring budget but continue to use the best materials necessary.  Once again the riser is made up of 4" ceramic tubes and encased in a refractory mix that will act as my vertical thermal mass. This time it will be housed inside an aluminum truck box  and used inside an aquaponic greenhouse previously mentioned.  As pictures are worth the proverbial thousand words, feast your eyes on the build so far!
As you can see in the attached photo the 4" ID ceramic core rises 40" above the 3.25" x 3.25" ID thick walled firebox.  You will also notice two angled secondary air inlets that intersect the riser and horizontal firebox along with the 3/4" FIP at the bottom of the modified 30 pound inverted propane tank ( the bottom secondary air intake also acts as a fly ash extractor which keeps the 100 pounder repurposed propane tank bell clear of ash) This has proven successful in the Frankenstove Mark 5 and has been made more compact as previous experience in ash collection is very small compared to expectations.  Also it was made smaller to fit inside the available aluminum box.
The refractory is a blend of perlite, fireclay, silica sand, portland cement (and finely granulated refractory that was used to build Frankenstove Mark 2( recycled proven material to keep production costs down).

I know what you are thinking... why the second angled secondary air inlet? I thought you would never ask.  If you've been following this thread from the beginning, I was experimenting with atmospheric steam to reduce NOx and improve moisture in the burn tunnel.  Well I thought I would give that another try once I get this build dialed in. If I don't need it a simple cap will seal its fate.

So, this refractory core will take a while to cure as I do not wish to make the same mistake I did with my original Frankenstove Mark 1 causing the refractory to crack due to heat stress.  I am also working on building a better wood pellet basket and an improved secondary ember burning containment/ primary ash catcher!

I know this build is beyond the skill set of a lot of  the basic designs of rmh builds and many on this site say that a 4" riser system cannot function like larger diameter riser designs but this thread is testament to relentless trial, error and "what - if " thought experiments. This build can be done with a grinder, drill and a basic knowledge of welding along with basic hand tools and I encourage anyone who is handy to give this design a go with safety as the prime directive.

Stay tuned and thank you for 6,000+ views on this thread!

Well Fellow Permies, The refractory cement mixture has been given 24 hours to set and it is time to SLOWLY cure it by introducing a slight warming of the casting. To do this, I found one of my smallest propane torches and set it up to send heat down the centre of the square burn tunnel and then flow up the riser by convection where a slight restriction at the top would keep the riser temperature warm enough to speed up the drying but less than 100*c (UNDER BOILING POINT OF WATER ( 212*F) so it doesn't cause the casting to crack during the curing process.  Although the temp spiked at 160*F in the riser, I managed to get the riser temp to regulate around 130*F  by moving the lit torch back towards the mouth opening of the burn tunnel.(See Photos). I have left the 10" cardboard post setting tube forms in place to insulate the cast while it slowly cures. I also strengthend the vertical riser with reinforced with rebar and wire screening 1/4" (hardware cloth) during the pour  to keep chunks from falling off in the future. I will remove the form later once I can be certain everything is well cured.  I once worked for a chemical company that had to spray a refractory mix on the walls of a large thermal oxidizer and curing the refractory meant slowly adding heat to cure the mix once application was complete. This was called building a heat profile. Although I lack the engineering background, the process was to keep the internal temperature below the boiling point of water for 24 hours.  So, my rather small "thermal oxidizer" aka riser tube will also be kept below said temp until I can feel heat permeating the outside of the form  I will also drill a  borehole in the centre of the outer ring of the refractory mix to confirm that the heat is migrating in a radial direction. currently this temperature is around 101*F so I know it is working. you can also notice the colour of the cast refractory is also lightening up which suggests that there is less water in the mix.  i know that it is very important to do this process and not to rush it, as I experienced a crack in my original Frankenstove creation as I failed to dedicate due time for the mix to cure and no regard to building the heat profile to drive out excess water.  Steam is a powerful destroyer due to extreme expansion.
I will probably go through  6 bottles of propane to achieve this heat profile to be sucessful... that will give me time to fabricate the 100 lb bell from a repurposed propane tank in the next few days.
slowly but surely  Frankenstove 6 will come to life. stay tuned for more developments as the build continues

Very interesting build, did I miss read the bit about using re bar in the riser?

On your last build, have I missed what your actual layout is? or build steps?  It just appears to be there,  as well as a proposed Bell? ( heat extraction chamber ) or is this your tool box, down the road.

You also mention this list,  "The main materials will be one 100 lb propane cylinder, one 30 pound cylinder, some square tubing, ceramic tubing and refractory cement and an aluminum toolbox!"   But it would appear that you have used an sannen tube fairly extensively? Or maybe I am missing something,   And lastly, do you expect the steel tube ( where your torch is shown ) to last for the life of the stove? Just curious?  Maybe this area of metal comes out during your build.  If this metal is allowed to spall out of the system, does that change your dynamics of heat production with this unit?

Sorry for all the questions, about your interesting design.  Lastly do you intend to regulate the temp or amount of wood pellets burning, by adjusting the air inlet? with More Air equaling more pellet burning. Or is this one basic level of pellet burn?   Am curious.

hello Mr. Weinberg,

Thank you for your barrage of questions regarding my "Frankenstove Mark 6 vertical thermal rmh" It is a pleasure to discuss my design and I look forward to you sharing your ideas about my build with me in "Moosages"  rather than involving the general population on permies.

I am using this thread as a "soft Launch" of my "Frankenstove Franchise" of Vertical thermal rmh prior to a series of " from the Ground Up manufacture on a youtube site and monitize my efforts on the plans.  This is not your typical build of the "mud and straw builds" that are ubiquitous on permies and I have a profound dislike of using thin gauge oil barrels as bells for the builds I see on this site.

1. my layout is similar to the F5 build earlier up the thread. my steps will be divulged in a future video series. Everything in the build sequence has been photographed and will be released, rest assured.
2. the bell will be the venerable thick gauge 100 lb. propane cylinder that will be welded to the section of the 30 lb. base.
3. the 4" heavy wall burn tube remains.  previous use of this material has survived relentless use in the F5 for years up to temps of 960*F and temp cycling to room temp daily. I have experienced some spalling on my smaller square tube burn chambers of previous builds of smaller dimensions.
4. there is some temperature adjustment via a proprietary sliding pellet basket; which has taxed my creativity to the limit that I will get into the video.
Thank you for your engagement in my design
Peter Chauffeur

Fox James wrote:Very interesting build, did I miss read the bit about using re bar in the riser?

Hi James, Short answer, yes, three 1/2" spaced at 120* apart to take the stresses of off vertical rotation to move it like an acetylene cylinder 50 metres  from the Frankenstove Laboratory / Manufactorium " to greenhouse.
these rods are located at the extreme outside of the 10" sonotube and are fastened to 1/4 inch hardware (wire) cloth. which will prevent parts of the refractory from falling off due to continous thermal cycling daily. (preventative measures ) You will have to wait to see how the resultant casting of my refractory turns out when I remove the sonotube form. Expansion / contraction should not cause a problem due to its maximum distance from the ceramic core.

More progress in the Frankenstove Mark 6 today!  The long awaited BELL was cut to fit over the riser and rough spots ground down ( the welds that held the base and valve protector ( which was repurposed to be the base of the 30 pounder)) I am also working on a manual winching system that will lift the bell above the riser and then lower it into position for welding to the base of the RMH. Here are some pictures of today’s progress

Hello Fellow Permies,

Today, progress was made by securing a method to set the bulky (and heavy) Bell over the riser using an old crank winch from a boat trailer and the trusses of my Manufactory (tool shed). This allows for a safe and secure lift so one person can do the job alone.
Using a plumb line, the burner / riser assembly was centered and the bell was raised using a Tee fitting on the top of the bell. See the pics below as pictures are better illustrations than words. This method of placing the bell has been used in the Frankenstove Mark 5 build and there is a slight swing of the bell as the riser assembly IS directly under plumb line. The bell will be lifted off as this was done to insure the whole RMH would fit inside the aluminum box.
Measure Twice, fit, Remeasure again and celebrate the process before the welding begins!

Hello Fellow Permies and “Frankenstove vertical RMH” enthusiasts!!!

Today was an absolutely exceptional day as I literally rolled “Frankenstove Mark 6” out of the Manufactorium and did an initial burn /test fire using hardwood pellets.  Using the wood pellets as the fuel source to continue the curing process will give me an idea as to how fast temperatures increase instead of propane which would mean using a “Tiger Torch” and may add way too many BTUs to of  refractory core too fast and do damage which is what I’m trying to avoid. Experiencing the increasing volume of the “roar” of this progressive and latest design was so rewarding and I cannot do it justice with words! A new design of a more robust pellet basket / carburetor has developed a consistent pulsating and reverberating echo that could be heard from a distance of 15 feet!, has made me feel that a giant leap for a rocket stove with a 4” ceramic riser a reality and welcome advance in the Frankenstove Family of low footprint vertical thermal rocket mass heaters!  
For those who haven’t been following this post from the beginning, it is important to “cure” the poured material by slowly cooking it with slow increments of heat and increasing time durations with cooling times between the cycles.
I am trying to avoid a “catastrophic failure event “ which occurred during my first “Frankenstove “ Mark 1 where a full blown fracture caused by uneven heat expansion.  This event caused a major crack in the refractory which I had to seal with high heat silicone which made me appreciate the “slow and steady” approach when dealing with proper building techniques and respect for research with respect to safely with refractory break-ins…. Without catastrophic breakages!!! Pun intended.
Also a new approach and design for a pellet basket / “carburetor “ has been designed to get around the “burnouts” I have experienced in my many previous basket designs and is interchangeable with the Frankenstove Mark 5 design. I took the interchangeable approach so I could evaluate its improvement even before the test firing of the Mark 6.
Upon rollout from the Manufactorium,  a propane torch preheated the combustion chamber and wood pellets were added down the feed tube and heated into nicely glowing bright orange embers with the classic horizontal flame accelerating progressively to the 90* where it hit the firebrick and proceeded up the ceramic riser. A short burst of smoke and then nothing but turbulent flames started up the riser. A short feed tube was filled with pellets and the roaring rocket sound amplified!  It was ant this moment I felt the elation,   And success that years of design through trial, error, thought experiments had cemented  my joy that this design has already exceeded my expectations!!!
So, please celebrate with me and view the photos below. The runtime of the first burn was jet to less than an hour with external burn tube reaching 700*F+ and top internal ceramic riser temp reaching 350*F.
An expected very small amount of steam was exiting the thin piece of sonotube ring at the base of the riser.

Hello Fellow Frankenstove Enthusiasts!

Epic Day here at the Frankenstove Manufactorium!!!

Today the bell was finally lifted above the riser and lowered into position over the riser, centered and welded together. To make a sealed unit. Yay!  

Then the unit was rolled into the aluminum housing to confirm fit and to determine where the 4” exhaust pipe was going to be located.

It was determined that the exhaust pipe will be located just to the left of the feed hopper which will keep it away from the double skinned polycarbonate of the greenhouse walls. Stainless steel flex pipe will then run the exhaust straight up and do a 90* bend and run out the gable end of the greenhouse using a B-vent.
Unfortunately, I have to go do a work contract and will be back in a month to finish up the build so please be patient and stay tuned!

Well done, looking forward to the first ignition…..

Peter Chauffeur wrote:This is not your typical build of the "mud and straw builds" that are ubiquitous on permies and I have a profound dislike of using thin gauge oil barrels as bells for the builds I see on this site.

I'm a big fan of horses for courses...deploying technology that is appropriate to the situation. In my case, I have a glasshouse I need to heat over the winter, but not every night. We only have freezing overnight temps about 20-25 times on average. So I built a 4" J-tube, "by the book" with cast burn tunnel, fireclay+perlite riser, a 30-gallon drum as the radiator (NOT a bell because there is no mass), and a cob bench with the flue piped through it. Materials costs were about $100 for castable refractory mix, fireclay and perlite. The drum was free from the local scrap metal dealer. The cob was free for the digging. I spent about a week or two building it, total labour around 12 hours.

It's been in service for 8 years now and I cut out the warped thin steel from the top of the drum and replaced it with a round piece of 5mm plate. Best griddle ever. I've rebuilt the burn tunnel with firebrick (the cast one disintegrated after three years) and replaced the heavy clay riser with a 5-minute one. So there was an additional material cost, maybe another hundred bucks, and about 3-4 hours to dismantle and rebuild the core. The drum is fine and gets a coating of linseed oil at the end of each season. It does exactly what it needs to do, which is to shed some of the extreme heat after the exhaust leaves the combustion zone, and enhance the system draft via the densification of the cooling and sinking gases. Temps on the cooking surface (did I mention what an awesome griddle this is?) approach 300 C. Readings on the side of the drum usually go from 180 down to 120 from top to bottom. This is not a bell. The thin metal is performing a function quite different from a mass of stone or brick.

The heat storage happens in the cob bench, which warms up to around 35-40 C during a burn and is a really nice place to sit on a cold, rainy night. Someday I might tear it down and replace it with a stratification chamber using barrels cut in half lengthwise, because cleaning out the pipe is not fun and there is a bit of ash in there that is hard to reach from the cleanout ports. But the basic design is performing brilliantly, and the humble RMH should give many more years of service with minor maintenance.

Hello Permies!  

Frankenstove 6 is ALIVE!!!  But with a new name. May I have the honour of introducing The ALOHA RMH.

It is with extreme gratitude and excitement that I wish to announce the successful launch and operation of the much awaited Frankenstove 6  (ALOHA RMH) to make the journey from the “Manufactorium” to the aquaponic greenhouse!

I now have the opportunity to grow food year round due to this RMH novel design.

Thanks for all your encouragement and the 6800 views on all my previous builds from the original F1 through to the F5.

For those of you wondering why the name change is because I wanted the name to reflect the warmth given off by this design.

ALOHA RMH has taken all the lessons learned from every single one of the Frankenstove series and refined them to make this new brand possible and I owe a special thanks to Permies for giving me the opportunity to pursue this experimental build to fruition!  

I plan to do a build video on ALOHA to explain how you can build one completely from repurposed materials ( except for the ceramic riser)

Be warm, Be safe, be kind…

That is a bit of a tease Pete, we need more pictures or even better, a video?

Patience Permies;  all will be revealed.

The ALOHA RMH was specifically built for my greenhouse/ aquaponic garden. The design compact, low footprint and totally manufactured from repurposed, easy to find materials that anyone can get in their hands on. The exception to this statement is the ceramic 4” ID refractory tubes.

Anyone who can operate a drill, grinder and basic welding skills can build this!
Stay tuned patrons of Permies!
Stay safe, be warm, be kind

Phil Stevens wrote:

Peter Chauffeur wrote:This is not your typical build of the "mud and straw builds" that are ubiquitous on permies and I have a profound dislike of using thin gauge oil barrels as bells for the builds I see on this site.

I'm a big fan of horses for courses...deploying technology that is appropriate to the situation. In my case, I have a glasshouse I need to heat over the winter, but not every night. We only have freezing overnight temps about 20-25 times on average. So I built a 4" J-tube, "by the book" with cast burn tunnel, fireclay+perlite riser, a 30-gallon drum as the radiator (NOT a bell because there is no mass), and a cob bench with the flue piped through it. Materials costs were about $100 for castable refractory mix, fireclay and perlite. The drum was free from the local scrap metal dealer. The cob was free for the digging. I spent about a week or two building it, total labour around 12 hours.

It's been in service for 8 years now and I cut out the warped thin steel from the top of the drum and replaced it with a round piece of 5mm plate. Best griddle ever. I've rebuilt the burn tunnel with firebrick (the cast one disintegrated after three years) and replaced the heavy clay riser with a 5-minute one. So there was an additional material cost, maybe another hundred bucks, and about 3-4 hours to dismantle and rebuild the core. The drum is fine and gets a coating of linseed oil at the end of each season. It does exactly what it needs to do, which is to shed some of the extreme heat after the exhaust leaves the combustion zone, and enhance the system draft via the densification of the cooling and sinking gases. Temps on the cooking surface (did I mention what an awesome griddle this is?) approach 300 C. Readings on the side of the drum usually go from 180 down to 120 from top to bottom. This is not a bell. The thin metal is performing a function quite different from a mass of stone or brick.

The heat storage happens in the cob bench, which warms up to around 35-40 C during a burn and is a really nice place to sit on a cold, rainy night. Someday I might tear it down and replace it with a stratification chamber using barrels cut in half lengthwise, because cleaning out the pipe is not fun and there is a bit of ash in there that is hard to reach from the cleanout ports. But the basic design is performing brilliantly, and the humble RMH should give many more years of service with minor maintenance.

Hi Phil, I have to admit I enjoyed your posts but I have no idea what your reference to horses have to do with rocket mass heaters. As for “building it by the book” I would appreciate you provide information where it suggests a metal riser and the heat specification for your oil drum and where it says to cut off the top and adding 5mm plate. I’m certain that the seam of your oil can will be the next thing to heat fail due to thermal cycling. I think your book needs a re- edit!
I do agree with you that the thickness of oil drum barrels are way too thin to take the massive amounts of heat exiting the riser and there is a need to add a thicker flat plate of steel to prevent your ceiling or home burning down due to a melt thru during operation.
I also agree that a metal riser is a poor decision to use which is why I chose to dole out $100 for the proper ceramic 4” I.D.  Tubes to withstand the heat.
Choosing a 100 lb. Propane cylinder for the bell was the engineering product of choice as their thickness and quality of metal are designed to take massive amounts of heat while containing propane and preventing a rupture leading to a BLEVE (if the pressure valve fails)
I will include a picture of the inside of my ceramic riser shortly after shutdown looking down the 3/4” threaded “scully fitting” that used to hold the brass valve. The glowing red area is where the horizontal burn tunnel hits the vertical ceramic riser.
My design is solid, takes a bit of craftsmanship and safety engineering so I can leave it to heat my home and hot tub while I’m out enjoying riding my horse in the Great Canadian pacific northwest!
Build it right the first time. I strongly suggest you get an empty , devolved 100 lb propane cylinder for and replace you re-engineered oil can for safety’s sake.
Be safe and be warm.

"horses for courses...deploying technology that is appropriate to the situation."

You would not use a thoroughbred to pull a plow, or a Percheron to win a race.

Peter Chauffeur wrote:
Hi Phil, I have to admit I enjoyed your posts but I have no idea what your reference to horses have to do with rocket mass heaters. As for “building it by the book” I would appreciate you provide information where it suggests a metal riser and the heat specification for your oil drum and where it says to cut off the top and adding 5mm plate. I’m certain that the seam of your oil can will be the next thing to heat fail due to thermal cycling. I think your book needs a re- edit!

OK, first of all:  I never said anything about a metal riser.

"Horses for courses" is a common saying about matching one's needs with the resources available. When I needed occasional heat in a glasshouse and had access to most of the materials for free, there was (and still is) very little motivation for me to radically overbuild the thing. I accepted the 100 L oil drum as a consumable and at the rate of material depreciation I'm observing I should get at least another ten years out of it, and I fully expect it to fail from rust, not thermal cycling. If I'm wrong, I will let you know.

The "book" is the product of many years' worth of community knowledge, most of it gained via this forum but also the publications by Evans, Jackson, Wisner, etc. When I describe my build as following that template, it means that I used the tested and proven ratios for the J-tube dimensions, as well as for the mass bench. This "book" is always evolving, but I don't think there's any reason to claim that replacing the warped and rusting surface of the drum amounts to a deviation from the spec. It's maintenance plus upgrade, in my view, sort of like putting a better tyre on your bike when the old one wears out does not mean you suddenly no longer have a bike.

Peter Chauffeur wrote:I do agree with you that the thickness of oil drum barrels are way too thin to take the massive amounts of heat exiting the riser and there is a need to add a thicker flat plate of steel to prevent your ceiling or home burning down due to a melt thru during operation.

I would say that the thin top surface was a liability for my application. It was not flat to begin with, and was extra hot in the middle, which made it suboptimal for cooking. I got it to glow dull red once or twice with a crazy hot fire, so it might have approached 600 degrees, but in ordinary operation 300 is the max. Mild steel melts at 1200. It also spalled somewhat during use and rusted in the off season. An indoor installation probably would not have seen much of this. Anyway, 5 mm plate has fixed those problems. It still spalls and rusts a bit, but there's probably 25 years or more of useful life in that plate. Melting is almost out of the question, since the 4" burn tunnel simply does not develop that kind of thermal output *and* because steel radiates the heat away quickly. But remember that this radiation is a design feature of the simple J-tube RMH.

Peter Chauffeur wrote:I also agree that a metal riser is a poor decision to use which is why I chose to dole out $100 for the proper ceramic 4” I.D.  Tubes to withstand the heat.

I would never use metal for a riser. I started with perlite and fireclay, then upgraded to a 5-minute riser. I think the insulative performance of my riser is good enough for the application. Again, if and when it bites the dust, I can carefully consign it to its next life entombed in a brick and replace it...dozens of times for the cost of insulative ceramic tube that I would need to ship internationally if I decided to use it.

Peter Chauffeur wrote:Choosing a 100 lb. Propane cylinder for the bell was the engineering product of choice as their thickness and quality of metal are designed to take massive amounts of heat while containing propane and preventing a rupture leading to a BLEVE (if the pressure valve fails)

The time and expense of procuring one of these, plus how much harder they are to cut to size, means that this was never a candidate for my application.

Peter Chauffeur wrote:I will include a picture of the inside of my ceramic riser shortly after shutdown looking down the 3/4” threaded “scully fitting” that used to hold the brass valve. The glowing red area is where the horizontal burn tunnel hits the vertical ceramic riser.
My design is solid, takes a bit of craftsmanship and safety engineering so I can leave it to heat my home and hot tub while I’m out enjoying riding my horse in the Great Canadian pacific northwest!
Build it right the first time. I strongly suggest you get an empty , devolved 100 lb propane cylinder for and replace you re-engineered oil can for safety’s sake.
Be safe and be warm.

Thanks for your concern, but I have made an independent evaluation based on eight years of performance about how fit for purpose my RMH is and don't intend to do anything major design-wise. Like I said earlier, the bench might get an upgrade to a stratification box next time I have to clean the ash out of the pipe.

Before you dismiss the oil drum radiator design out of hand, consider how many of them are out there in the real world, quietly just doing what they need to do. They didn't cost much to obtain, they were easy to modify, and there won't be a lot of drama when they need to be replaced as part of ordinary maintenance. If they were really as dangerous as you suggest, we would be hearing the tales of woe by now, and the reputable designers and builders like the Wisners, Uncle Mud, and others, would be advising against them. For example, this one seems to be working stunningly:

Hello Phil,

First, thank you for your poignant definition of “horses for courses”, I now have a new phrase I can use when it comes to a basic design using the bare minimum of materials. The problem with your saying horses for courses” is that horses don’t play with fire!

Second, I misread your “cast riser” as cast iron!  Oops. My first two stoves had metal riser ( high temp 3” muffler pipe) that had a surrounding poured refractory casting surrounding it. The metal pipe suffered thermal destruction and I documented that several times on this thread.

Third, we can agree that an oil drums are the bare minimum for enduring the heat blast exiting the riser and concentrating a lot of heat which caused further distortion and stress on the thin gauge bell that are ubiquitous in conventional rocket mass heaters. These are copies in “by the book” the builders you have suggested and it does have an overlooked safety issue.  As you have described from your experience, the oil can you used needed to be replaced with a 5mm flat steel plate.
Oil drums were made and designed to transport oils and other liquid ingredients at normal earthly temperatures using the oil drums as a “one-off” means of getting to the customers locality in a relatively safe manner. Oil drums were not designed to take heat stress cycling and combustion gasses. So, from a design perspective they are actually a poor choice for Rocket Mass Heaters heat output is far beyond what the oil drums were designed for.
Yes, oil drums work and sometimes right at the envelop of thermal failure like your stove did where you needed 5mm of flat plate steel to modify your “eight year build”.  Just because “ by the book “ builds or “that’s what the authorities did! “ on the subject are using, doesn’t mean there are better alternatives. That is what I’ve done in developing 6 different rmh’s over my years looking at the deficiencies in the designs of others. Every design isn’t perfect but if you don’t look at the designs of others and ask yourself, “ What can I do differently to build mine better?”, then you are not taking the dialogue of building a better more useful RMH for others to ponder on their development for better builds of their own.

Fourth, I understand that rebuilding/ modifying a RMH can be a huge undertaking and usually involves an on-site rebuild /repair and the cost to do it may be prohibiting to the builder that used the cheapest available, but let me ask you to consider this question. If I was given the knowledge that “burn - thru” of oil drums are a possibility and some other builder said, “ Hey! All you amazing people building these rmh’s that you can replace sketchy oil drums with a safer bell made from a 100 lb propane tank that you can get from a junk yard for $20?”  Would you not consider a safer alternative?  I would.

Fifth, I know that my builds aren’t something you build on a weekend with some good old boys and a case of beer!  It took time. It took problem solving. It took documentation to put it on this site so other, open minded researchers and enthusiasts could see that there are other designs out there that have different attributes that may be out there and the road of development is documented along the way! This thread is the culmination of many years of building and operation of my adventures of designing and building gravity wood pellet feed, space conscious, Rocket Mass Heaters that, can be used in house and one to heat an aquaponic greenhouse. I have taken this build thru 6 evolutionary builds; on one single thread so there is continuity that others can see. I refuse to sit on my laurels and admit what I’m doing is, good enough!”  Of course not! RMHs make sense for relatively cheap environmentally sustainable heat for anyone willing to consider them.  However, if you look to push the “mud and straw builds and consider more “appropriate technology” which by my definition means using the best available materials “ you will come to the conclusion that RMHs have to develop from what is to what is MORE possible.

Finally, your design works for you! You do you. I am proud of all my designs; for all that went well. and more importantly for all that didn’t go well.  What I’ve learned and painstakingly tried to guide others in the possibility of their being to undertake a build on my design. My innovative spirit and tenacity to keep building and posting on this thread that has been viewed over 7,000 times is testament that other Permies see the need for innovation on the basic designs on this site. Is my quest for a better RMH over? No. There are many avenues that my designs you have seen on this thread and some I have  kept back pending further review and development. It is because I have built a RMH that can push past the status quo challenging what a person can build with ingenuity and basic tools (drill, grinder,welder( time and patience!))
Stay tuned, I’m still pushing the envelope on what my RMHs can achieve. Enjoy where you are in this journey, my designs have places to go! And I’m certain that there are those that are interested in following!
Thank you for your interest.

Be Safe, Be warm

Hello Permies!

Warm wishes for a new year for those currently using rocket mass heaters and those interested in building one of their own for sustainability and economy!  

I now have 3 operating units of my own design that currently heat my shed, my house ( and hot tub) and finally my greenhouse.  All of these designs have been massaged thru my experience, trial and error, safety considerations and the occasional “ah—ha! Moments”

Even though there are those on this thread consider these designs to be “ too advanced” and revolutionary from the “by the book mantra” due to straying from the status quo of what a Rocket Mass Heater should look like or be like, I will continue with my stand that there are many people on this site that need to know that rmh’s do not need to be massive constructions and square footage space eaters.

There is no question that these designs challenge the “ mud and straw conventional approach”. This  build also requires the ability to use a welder and some hand tools. I have documented a from the ground-up build on this page so others can follow the process.