Building code compliant prefabricated rocket stove, safety tested

Hello everyone!

Without coming across as too blatantly self-promotional here, I just want to drop some information here on Permies about a company and product my father and I have fully dedicated ourselves to - the Rocket Heater.



In a nutshell, it’s a pre-fabricated, shippable, ready to use rocket stove, designed to be used with both pellets and wood, thanks to our pellet hopper attachment.

Rather than just create a rocket stove you can buy online, my father and I wanted to create a rocket stove that was building code approved - something that was not only sustainable and energy efficient, but that gave people needing to meet certain safety standards an option for heating and cooking with a rocket stove in their homes.

The Rocket Heater is a Nationally Recognized Testing Laboratory (NRTL, a division of OSHA) listed and UL-1482 compliant rocket stove that you can purchase online from our store, and have shipped to your door within 30 days.



Why a Rocket Heater? Getting Around Red Tape and Building Codes

For most Permies, the rocket stove is a tried and true concept. With very little fuel input, the rocket stove burns highly efficiently, utilizing the exhaust pipe to get the most heat output for the least amount of wood input - less splitting wood, more heat, and a fuel efficient burn that won’t keep you hunched over a maul all season long.



Then of course, you can incorporate the concept of the thermal mass into the rocket stove, so that all of that heat is gradually dispersed into your living quarters, either via a big cob bench, a wall, or a heated floor even.

The only real problem that people can run into sometimes with rocket mass heaters and rocket stoves is that the designs are not always building code friendly. I'm throwing this out here because one of the hardest things people are having trouble with is the safety testing, building codes, and insurance.

When my father and I started our company, (RocketHeater.com), we did so with the objective to bring innovation and certified professionalism to Rocket Heater technology. We’re using the most advanced scientific methods to take the Rocket Heater to its next logical conclusion in the evolution of the technology.
Don’t get me wrong, I love it when people are able to DIY a rocket heater, but for many folks who live under the thumb of pencil-pushing code enforcers or who need insurance compliance, building one themselves just may not be feasible. Furthermore, I personally think having a company with professionals and staff that are certified and trained and make and develop rocket heaters for a living really adds a lot of credibility to the technology.

What we want to do is to give those folks that have to comply with building codes and insurance safety standards a chance to have a rocket stove in their homes too, with all of the tested and proven science of our design, and best of all - all of the fabrication and shipping - done by us.

Products

Liberator Rocket Heater
NRTL Listed to UL-1482 Safety Standards!
Get it here.




When you purchase a Liberator Rocket Heater you will get a FREE outside air intake adapter AND a FREE Pellet Hopper Adapter! This sale offer is a limited time offer and will end very soon!

Liberator Pellet Hopper Adapter



Drops in any Liberator Rocket Heater (with outside air intake adapter installed) and allows you to burn an entire 40 pound bag of pellets for over ten hours!

Read more about it here, and order it here.

I like it

It looks a lot like a similar concept as my original multi-fuel rocket stove with internal mass.

Have you thought about marketing a barrel top Dutch oven? I was burning pellets with huge success and wood and bio mass in my rocket and I've documented it all, check my YouTube or my "compact RMH with Dutch oven " thread here on permies , I've baked a pie and a pizza during development tests of my prototype.

It's good that you have the means to make it more available and spread awareness for energy conservation

John McDoodle wrote:I like it

It looks a lot like a similar concept as my original multi-fuel rocket stove with internal mass.

Have you thought about marketing a barrel top Dutch oven? I was burning pellets with huge success and wood and bio mass in my rocket and I've documented it all, check my YouTube or my "compact RMH with Dutch oven " thread here on permies , I've baked a pie and a pizza during development tests of my prototype.

It's good that you have the means to make it more available and spread awareness for energy conservation

Hello John and thanks for your input!

Right now we just have the 16" diameter cooktop and I've found that you can use it like any natural gas or electric stove. To lower the temp you just move the pan/pot off to the side since the hottest part is in the center. We can't make any design modifications other than drop in adapters because the testing lab hits us with a 150 dollar design change fee for every little change. We wanted to add a third heat fin to the top of the horizontal burn tube to better radiate heat and we were charged 150 dollar fee for the design change. Even though we have different models coming down the road, until some people at least start buying what we have we wont be able to afford further development. Our company is a really lean startup, my father cashed out his retirement accounts and I foregoed college to start this business and hence we dont have a lot of money to play with. Now I dont want to self patronize myself but if you do read up on them, download the manual, etc. you can at www.rocketheater.com

On the top plate of this heater we get it to run at a smooth and constant 550 degree's F. for over ten hours on one bag of pellets. On wood we can get temperatures to exceed 700 degree's on top on a really good day.

We have taken temperatures of the internal burn chamber and we are exceeding 1200 degrees F. We determined this by placing aluminum slivers that melt at 1200 F. across the length of that horizontal burn tube and they all melted. Our pellets are suspended by an expanded metal stainless steel burn grate and right now the burn grate is glowing, and the heat rating of 304 stainless steel is 1700 degree's F and we are getting mild corrosion on our stainless steel so we know that our temperature is exceeding that. Our fuel/wood pellets burn blue somewhat like a natural gas flame.

Right now we are getting a burn grate coated with plasma jet ceramic. Basically, we send it off to a company that takes ceramic and heats it into a plasma, then sprays it on our grates via a plasma jet where the ceramic instantly bonds to the stainless steel. If this doesn't work then we will have to use vapor deposition of rhenium or hastelloy which is the same coating that rocker nozzles and RAM jets use.

We are also experimenting with using Aerogel-like materials for insulation for future models. We will keep everyone informed on our progress.

Great idea, are you afraid the metal will breakdown quite quickly with the high temps,( check out the forum about all failures with metal), have you checked into refractory metals to build the pellet grate with like molybdenum or such, is the riser insulated in this stove?

Hello again Anthony!

The riser is not insulated, however it is made of a very thick A500 grade steel and is more than sufficient to last an exceptionally long time. We ee no signs of corrosion despite over a year of good use.

The burn grate is made of 304 Stainless Steel which is a very good metal for heat resistance and should last quite some time, and when it doe at long last burn through its a mere 10 dollars to replace. However we have looked into vapor deposition and other high heat treatments, its getting so hot we are literally looking into the same technology that NASA, Raytheon, and other big time aeronautic industries use for rocker nozzle and jet turbines. However its a very. . . . . . Expensive process.

Hey buddy your stove looks fancy I would like to ask you a few questions.

1. What is your burn tunnel made of?
2. What is your heat riser made of?
3. what kind of 304 stainless steel are you using on your grates?

F Styles

Thank you for your questions and compliments!

The burn tube is made of A500 grade steel and we see no corrosion at all despite a full year or more of good use. This is because of an air-swash thats designed into the stove, a somewhat similar principle is used to keep the glass of conventional wood stoves clean. We also have welded heat sinks on to the side of the tube which keeps the temp just below the point of incandescence, which is when steel will start to undergo accelerated corrosion. The heat riser is also made of similar A500 grade steel.

We are using standard 304 Stainless Steel, NOT 304L which has a lower carbon content. Its stainless expanded metal thats specially shaped and modified to fit perfectly in a custom made burn grate suspender. This way when the burn grate finally does give way after a long time of hard use you can replace it for super cheap (were talking a ten dollar part that just pops in and out and requires no tools at all to change. A 4 year old could do it).

A500... cold formed steel is very industry standard carbon steel. I believe there are different grades of A500 but i do not think there is any difference in performance where you are using it.
Wow you are getting blue flames?... It sounds as if you are getting impressive heat generation from this little stove. Looks as though from your description of the color of flames and aluminum melting test you are exceeding 1200 and you say you know even higher than 1700 degrees F is that correct?

Sky Huddleston wrote: We have taken temperatures of the internal burn chamber and we are exceeding 1200 degrees F. We determined this by placing aluminum slivers that melt at 1200 F. across the length of that horizontal burn tube and they all melted. Our pellets are suspended by an expanded metal stainless steel burn grate and right now the burn grate is glowing, and the heat rating of 304 stainless steel is 1700 degree's F and we are getting mild corrosion on our stainless steel so we know that our temperature is exceeding that. Our fuel/wood pellets burn blue somewhat like a natural gas flame.

Yes, the 304 Stainless Steel Burn Grate has a temperature rating of 1598 F. sustained temperature with no corrosion. However we are getting beyond that point because even the Stainless Steel is glowing and mild rust starts forming on the stainless steel after a while. But its a VERY chap part so even if you do have to replace them every so often its still cheaper than the electric you'll spend on a heating element in an electric pellet stove and is way more reliable. So the temperature is very likely exceeding 1800 F. because the stainless steel is glowing red. We are actively looking into long term solutions and may introduce a "heavy duty" burn grate down the road that will last indefinitely that you will simply be able to pull your old one out and put your new one in with nothing but your fingers, again a 4 year old child could do it. One of the things we looked at was a plasma spray coating with a temperature rating of 2000 F. and we tested a burn grate that was coated in a specially formulated ceramic thats heated to over 30,000 F into plasma, the fourth state of matter, and sprayed on as a jet stream of particles to form a thin ceramic layer over the stainless steel. This coating has a rating of 2000 F. and after one run it was burned off. Which is a shame, too. The coating was glass smooth, super affordable, and it took off all the sharp edges of expanded metal that can not be ground/sanded off. We were really hoping it would work, but it didn't. So the only other thing we can do is vapor deposition of rhenium, hastelloy, or platinum over the stainless steel burn grate. This vapor deposition technology is literally what NASA, Northrup Grumman, Boeing, and other top notch institutions use to coat rocket nozzles, high pressure high temperature SCRAM jet engine forcing cones, high heat ultra high performance turbine blades, and other things. Stainless steel MELTS at 2550 F. and so we are really pushing the limits here. And the crazy part is that we have yet to get a gas flue analyzer (specifically for CO output) for our own testing. Due to budget constraints from a lack of sales we can not afford one at this time.

Anyway, I dont want to get into too many details. We have a lot of things that are patent pending. And there will be more to come. However unless we start making some sales soon we will go bust. So if anyone here would be interested in or knows someone who would want a Rocket Heater thats NRTL tested and listed to UL-1482 standards please let them know. Our heater meets all building code and insurance requirements. Not to be self patronizing here, I dont want to come off as just some shamelessly self promoting attention whoring businessman. I sincerely have good intentions beyond profit and I will be more than happy to share knowledge, wisdom, and experience as time goes on. We are doing a lot more stuff, too, however Im not going to give out everything and show all my cards just yet. Lets just say that as this company grows I want to spearhead taking what the forefathers of the Rocket Heater, Paul Wheaton, Ianto Evans, and all the DIYers have done and really take the technology to an extremely high level of professionalism and hardcore science. We were actually going to go the the Alliance for Green Heats Pellet Stove Design Challenge this year, at Brookhaven National Labs, but we could not afford to go, again due to budget constraints and a lack of sales. If anyone here has interest in selling these as a salesmen, or has a store, etc. please let me know. My father and I are great innovators, builders, fabricators, craftsmen, whatever words you like, but Ill be honest we suck at sales and marketing. Again not trying to be self patronizing, but if you know anyone who would at least enjoy reading or watching material on it go ahead and get the word out. If our company grows good then we will win vindication for ALL rocket heater enthusiasts at the next years Pellet/Wood stove design challenge. We are dead set on going in 2017!

Also, we are developing many other (secret) projects and products related to this technology. So keep in touch here, on youtube, and facebook for all the latest updates. We dont update very much, as in once every few months or so, but when we do we come out with bombshell innovation!

And remember, if you ever run out of pellets this stove can burn wood just like any other rocket heater by simply pulling up the pellet hopper.

holy goodness 1800 degrees F? are you kidding me? For real are you really getting 1800 inside your system?

For anyone thinking of using metal to make a rocket stove, I'd like to draw attention to the information in this thread -

using metal in the burn tunnel and heat riser

F Styles wrote:holy goodness 1800 degrees F? are you kidding me? For real are you really getting 1800 inside your system?

That level of heat isn't uncommon in rocket heaters. In my own batch box design the highest recorded temperature has been 1180 degrees Celsius which converts to 2160 Fahrenheit. At the time, I wasn't even sure whether or not I was recording the hottest spot. Exit temperatures at the top of the riser are routinely over 900 C or 1650 F. So Sky is right, he really need to keep down those freaky temperatures inside the core or the whole thing would corrode like mad in no time. Whether or not a gas analizer would be satisfied about the results since the temps aren't really up to the phisical limit remains an open question.

id kick a pellet burning competitions ass- donkey. pellets are my specialy. you CAN achieve high internal GAS/EXHAUST temps without melting the SURFACES.

some people have melted metals because poor designs and no paint or no coating protection- so they think metal is doomed.

you have a good design- just like my compact RMH. i hate to give ALL my secrets but I was going to use CERAMIC COATED TITANIUM after my 100 hrs prototype tests and baking food experiments

That level of heat isn't uncommon in rocket heaters. In my own batch box design the highest recorded temperature has been 1180 degrees Celsius which converts to 2160 Fahrenheit.

Peter thank you for your input. I love ya like a Purist Rocket Stove brother. I completely understand the temperatures of a proper made Rocket Stove. My Rocket Mag stove is definitely getting well over 2000+ degrees F since i can see my fire bricks glowing orange. The reason I was showing such surprise in my above posts was that this person has said he is getting over 1700 degrees in an A500 carbon steel burn tunnel and heat riser rocket stove.

Peter van den Berg wrote:

F Styles wrote:holy goodness 1800 degrees F? are you kidding me? For real are you really getting 1800 inside your system?

That level of heat isn't uncommon in rocket heaters. In my own batch box design the highest recorded temperature has been 1180 degrees Celsius which converts to 2160 Fahrenheit. At the time, I wasn't even sure whether or not I was recording the hottest spot. Exit temperatures at the top of the riser are routinely over 900 C or 1650 F. So Sky is right, he really need to keep down those freaky temperatures inside the core or the whole thing would corrode like mad in no time. Whether or not a gas analizer would be satisfied about the results since the temps aren't really up to the phisical limit remains an open question.

If our max temp was only 1650 F. then there wouldn't be much of a problem. However the real hottest section is the stainless steel burn grate when using pellets. We weld cooling fins on the walls so the tubes surface itself never gets too hot to corrode, plus the pellets only burn in the center of the tube so the heat and fire never really contact the tubes surface directly. This is similar to an air-swash principle and it prevents corrosion.

In our scientific experiments we've found that the geometry of airflow and oxygen input is more important than insulation, though both are beneficial.

Sky Huddleston wrote:If our max temp was only 1650 F. then there wouldn't be much of a problem. However the real hottest section is the stainless steel burn grate when using pellets. We weld cooling fins on the walls so the tubes surface itself never gets too hot to corrode, plus the pellets only burn in the center of the tube so the heat and fire never really contact the tubes surface directly. This is similar to an air-swash principle and it prevents corrosion.

In our scientific experiments we've found that the geometry of airflow and oxygen input is more important than insulation, though both are beneficial.

Interesting. I also found out it would be possible to use steel at some places given that the environment didn't reach critical temperatures and/or low carbon values. Still I would like to know what a competent gas analizer shows. Pity you weren't able to afford such a device (yet).

By the way, I use a piece of steel duct now for the secundary air supply in the latest iteration of my home heater. This is situated in the fire itself but cooled by the air which is running through it. Also, I think the fact that it is completely closed in by flames when the fire is running there isn't much free oxygen at the spot while the burning of volatiles is further down the system. After two months of using in my home heater every day it's still not heavily corroded and actually looks surprisingly sound but I am planning to produce a spare one out of SS 304, just to be sure. It isn't a large piece and not complicated to make, and a 4 year old could change it out so to speak. Provided the heater is cold, obviously.

Sky
thanks for reply, I have been looking for a different way to heat my home, and was preferring to switch to pellets, looked at the pellet stoves but they eat so many pellets it would not be feasible, most pellet stoves out there are very expensive and use a lot of pellets, I currently Burn wood live in Minnesota and need to heat a 2500 sq ft house, looked in using coal but hard to get...anyways then I stumbled upon rocket stoves and started investigating and doing research on them and here I am, started having ideas of building one myself but then I ran into your info and got me thinking...I need to be able to run a stove 24/7 to heat my house and my house is a rambler style with basement my current wood stove is hooked into my duct work with blower,and is located in the basement, I was thinking if a person could make a sheetmetal box around your tank and hook up blowers to move the hot air through the ductwork???, I was watching your video, does the bottom plate remain closed? it draws air from the tube with pellets in it? do you ever get back burning or smoke back into feed tube? I was watching a guy on youtube (Mike Knop) who had a good design of a pellet rocket stove feeding it pellets but I think he was having problems somewhere? I am looking for a pellet unit that would not use so much pellets....the ones on the market out there to heat my house would use anywhere from 5-13 lbs a hour...that's way to expensive for me I would be happy to get by with 3 bags a day or less in my big house. so do you think your stove would work somehow for me? could I hook it up to a masonry chimney ? the only other thing I question is how long the metal is going to hold up with the high temps it puts out?
thanks

The metal is going to hold up fine, we've used ours for over a year now with no signs of any corrosion.

We heat our 1800 square foot shop, which has very poor insulation, high ceilings, and single paned skylights that let massive amounts of heat out, and a sliding door with half inch gaps all around, with ease. So it will do a 2500 house, if its decently insulated, quite well. Our heater can be hooked up to masonry chimney's. For info on that our user manual can be downloaded from our website www.rocketheater.com

There is no smoke back at all and it takes less than 30 seconds with a propane torch to fire our heater up, and thats without preheating the draft. A single bag of hardwood pellets, which is 40 pounds, lasts us over ten years. So you should get by with 2 bags a day! Air is drawn around a smaller tube that goes inside the square tube, the smaller tube feeds pellets and the larger one around it, which is the visible one you see, supplies air. In the video above I show how to install the pellet hopper.

And if you have the skill to build a metal box around it with a fan you most definitely could hook it up to your ductwork, it would be a lot of work and you would have to insure that you can still access to top of the hopper and the front ash cleanout door. And yes, the ash cleanout door does remain closed at all time except for cleanout of ashes. I would also recommend, if you're going to spend the time and money to build a box with a fan, go ahead and insulate the box with mineral wool!

We've come very close to perfecting our pellet stove design, it feeds reliably 100% of the time even on really bad quality pellets, and the pellets burn very hot for a long time. The only way we will be able to move forward from here is when we get the money for a gas flue analyzer, which is over a thousand dollars! Even once we do get one its going to take many months to figure out a truly "perfect" design, but I do know that we are close to that anyway. PLUS once we do get our design absolutely perfect we will be able to sell you the new style of burn grate so you can just swapp out the old one in your stove. This way you can get very good efficiency from our current design, then once we get our burn grate really good we will be able to sell you the new style for pretty affordably. Right now we have a orange/blue fire and my goal is to get a perfectly blue flame, make it look like natural gas. But thats a long term goal that will take at least a year. In the meantime I am still very satisfied and confident with our stove as it is and I heat my buildings with them. Truth be told, we are already burning off ALL the volatile organic compounds and we are completely smoke free within a couple minutes from startup. What I'm trying to do from here on out is burn up ALL the Carbon Monoxide, we are already getting very good CO levels as it is but like I said we want to burn as clean if not cleaner than the best natural gas furnaces money can buy. Like I said thats gonna take a year or three.

So for now our design is still very good and I am confident you'll be ecstatic with the performance! And like I said all our products are 100% backwards compatible so you will always be able to get our latest innovations down the road when they come out and hook it into your current stove.

Peter van den Berg wrote:

Sky Huddleston wrote:If our max temp was only 1650 F. then there wouldn't be much of a problem. However the real hottest section is the stainless steel burn grate when using pellets. We weld cooling fins on the walls so the tubes surface itself never gets too hot to corrode, plus the pellets only burn in the center of the tube so the heat and fire never really contact the tubes surface directly. This is similar to an air-swash principle and it prevents corrosion.

In our scientific experiments we've found that the geometry of airflow and oxygen input is more important than insulation, though both are beneficial.

Interesting. I also found out it would be possible to use steel at some places given that the environment didn't reach critical temperatures and/or low carbon values. Still I would like to know what a competent gas analizer shows. Pity you weren't able to afford such a device (yet).

By the way, I use a piece of steel duct now for the secundary air supply in the latest iteration of my home heater. This is situated in the fire itself but cooled by the air which is running through it. Also, I think the fact that it is completely closed in by flames when the fire is running there isn't much free oxygen at the spot while the burning of volatiles is further down the system. After two months of using in my home heater every day it's still not heavily corroded and actually looks surprisingly sound but I am planning to produce a spare one out of SS 304, just to be sure. It isn't a large piece and not complicated to make, and a 4 year old could change it out so to speak. Provided the heater is cold, obviously.

That's awesome that people like yourself , Peter are researching the longevity of metals. I used some stainless which is good condition but it's good to hear from others experiments and research to confirm validity of metals being feasible.

Anthony , mine is a miser when I run it on pellets but with the mass you only need to burn 5 hours to get 10 hours of heat, via thermal mass radiation. I had done 25 hours of pellet burning experiments, giving 50 hours of heat radiation, on a single bag of pellets. Plus I've done another 50 hrs burning regular wood and baking food! Lol. Check my pellet experiments on my YouTube

thanks sky...I may think this over and possible be interested in your unit

John mcdoodle, you live where its cold Canada, I live in Minnesota USA, not to far from you... I did watch your youtube videos, good results eh, how many pellets will it burn ? how much more testing are you going to be doing? are you going to heat your home with it? I am tired of burning all this wood with little efficiency... I burn 8 cords a year and that only heats my house part time the other is fuel oil....its getting old.. these rocket stove are very efficient , but I don't see many people heating there homes with them with just a rocket stove??? yeah mass heater rocket stoves but not many that heat with the stove hooked into there duct work somehow or fee standing... what you think about that? before I invest in doing that I want to make sure everything is safe and will work ? any ideas?

there are insurance and building codes sometimes.

myself- im no pro - im just fascinated and im learning so next season i will be ready

John Mcdoodle,
thanks for the info, how many pellets would you use in your model? you say pellets are your specialty ? whats the key to feeding it pellets, why do you think metal is not doomed in this high heat scenario?, most people out there believe it would be doomed in a little time of use.... I am just trying to get a grip on these rocket stove concepts...there is so much info out there a person has to really sift through it all, and make wise decisions... I really would like to get a rocket pellet burner for my house maybe the liberator as advertised, I just have to look at all scenarios and safety and all that..i wouldn't want to invest a lot of money and time to have to replace something in a year or 2....thanks

im just learning- i didnt say it isnt doomed- but my metal liners are fine for now and replacable.

i measured 3 or 4 cups @ 2 lbs (6-8lbs) and it burned clean and hot for 3.5 hrs ~ plus radiates from thermal mass - so do the math thats approx 1.7 lbs - 2.3 lbs per pound Hour consumption and 0.85-1.15 pounds per hour , including mass radiation , at 2hrs of radiation for every 2 hours of burning. 610F on the cook top . 210F where the chimney begins. And my feed tube holds more than that, and I have 2 different pellet burners. very good numbers but i want to do more tests

I agree with Peter that metal can be used in a rocket stove, even carbon steel when its used with in its operating temperature. We can not break the laws of physics no matter what we would like to think or experiment with. If any metal regardless what kind goes beyond its operating temperature then it will weaken.... I'm not even talking about melting temperature, I'm talking about operating temps. Voodoo or repeating it a bunch of times has not saved the many many folks that built rocket stoves and had them fail down the line when going over operating temps. I wish Mr Sky the best and hope he prospers in his venture. If Mr Sky is telling the truth and I have no reason to believe other wise, I can surely say from the temps he stated he is most certainly going over the operating temps of carbon steel. How long will it take to break down? I have no idea... 2 years? 3 years? We dont have all the analysis of his system to test to know so we can only guess when metal goes over its operating temp the laws of physics demands obedience.

I can say for sure that any system built from carbon steel cannot reach as clean and efficient burns as a proper made Rocket stove. A thread needs created to actually define what rocket stove actually is to inform folks because i have seen countless stoves built in a J configuration and slap rocket on the name and does not meet the definition.

I want to be clear to all that i love DIY, tinkering, creativity and innovation, but I do not like confusion and there seems to be alot of confusion when it come to the name Rocket stoves and heaters.

paul wheaton wrote:In another thread I wrote:

paul wheaton wrote:I've been asked to say something here.

Hi!

I have not read every spec of everything written here, but I did skim through it. This reminds me of a long conversation I had with the rather brilliant Peter van den Berg (who appears to already be on this thread).

The conversation goes like this: it is possible to design a rocket system with a lot of metal and have it be okay. It must be a very small system so that the temperatures will probably never exceed 1400 degrees F. Of course, at such low temperatures, it is difficult to get a non-smoky burn - but it can be done.

These forums have a parade of people that went down metal road and made systems that were amazing. For a while. And when the system failed in the middle of winter, they had massive heartbreak.

Rob's system comes to mind:

There has been so much heartache and so many disasters, it seems that there is a very strong push to discourage anybody from using metal in the burn tunnel and/or riser.

I know that we had a lot of people here at my place that were seriously loving on the pocket rockets for a few months - but after they all, universally, burned out their very thick metal tubes - we had to ban the use of this design here. After all: where does that burned metal go? The toxicity put into the atmosphere makes me very uncomfortable.

I think the people here are very much wishing to embrace another enthusiast. And, at the same time, direct your energy to a place that will have a strong positive long term result and not go through all the pain that so many others have gone through.

And, in the upcoming dvds, peter and i have a rather long discussion about this.

I think that the most important thing here is to keep in mind that steels are liquid at 2600 degrees, but they start to erode at even lower temperatures. F Styles provided this rather excellent list:

CARBON STEEL
Material frequently used in manufacturing. Due to its low resistance
to corrosion it should not be used in water, diluted acids or saline solutions. It may be used in some
alkalis and in some concentrated acids. Temperature limit 900° F (500° C).
Approximate Hardness: 90 to 120 HB.

STAINLESS STEEL AISI 304
Alloy with 18% Cr and 8% Ni is the material most used in the manufacturing of industry due
to its excellent resistance to corrosion, low cost and availability in the market. Its maximum operating
temperature is 1400° F (760° C). Due to Stress and Intergranular Corrosion, its continuous service
temperature is limited to 790° F (420° C).
Approximate Hardness: 160 HB.

STAINLESS STEEL AISI 304L
It has the same resistance to corrosion as the AISI 304. Since its Carbon content is limited to 0.03%,
it has less Intergranular Carbon precipitation and therefore less Intergranular Corrosion. Its
operational limit for continuous service is 1400° F (760° C). It is susceptible to Stress Corrosion.
Approximate Hardness: 160 HB and in some cases,140 HB.

STAINLESS STEEL AISI 316
This alloy with 18% Ni, 13% Cr and 2% Mo, offers excellent resistance to corrosion. It can have
carbonate precipitation at temperatures between 860° F (460° C) and 1650° F (900° C), under severe
corrosion conditions. Maximum recommended temperature for continuous service is 1400° F (760 C).
Approximate Hardness: 160 HB.

STAINLESS STEEL AISI 316L
It has the same chemical composition as the AISI 316 but its Carbon content is limited to 0.03%,
which inhibits the Intergranular Carbon precipitation and consequently, the Intergranular Corrosion.
The maximum service temperature is 1400° F (760° C).
Approximate Hardness: 160 HB.

STAINLESS STEEL AISI 321
Austenitic stainless steel alloy with 18% Cr and 10% Ni stabilized with Ti, which reduces the
Intergranular Carbon precipitation and also the Intergranular Corrosion. It can be used in
temperatures up to 1500°F (815°C).
Approximate Hardness: 160 HB.

STAINLESS STEEL AISI 347
Alloy similar to the AISI 304 stabilized with Cb and Ta to reduce
carbonate precipitation and
Intergranular Corrosion. It is subject to
Stress Corrosion. Has good performance in high temperature
corrosive
service. Maximum temperature: 1550° F (815° C).
Approximate Hardness:
160 HB.

MONEL
Alloy with 67%
Ni and 30% Cu, it offers excellent resistance to the majority of acids and
alkalis,
except to extremely oxidant acids. Subject to stress corrosion
and therefore should not be used in the
presence of fluorine
-
silicon acid
and Mercury. In combination with PTFE, it is used frequently in spiral
wound gaskets for severe corrosion services, such as Hydrofluoric acid.
Operating maximum
temperature: 1500° F (815° C).
Approximate Hardness:
95 HB.

NICKEL
200
Alloy with 99% Ni, offers
great resistance to caustic solutions, even thought it does not have the
same
global resistance of Monel. It is also used in spiral wound and
jacketed gaskets for special
applications. Maximum operating temperature:
1400 F (760° C).
Approximate Hardness: 110 HB.

COPPER
Material often used in small dimension gaskets, where
the maximum seating stress is limited.
Maximum operating temperature: 500°
F (260° C).
Approximate Hardness: 80 HB.

ALUMINUM
Due to its excellent resistance to corrosion and easy
handling it is very often used in manufacturing
gaskets. Maximum service
temperature: 860° F (460° C).
Approximate Hardness: 35 HB.

INCONEL
Alloy with 77% Ni, 15% Cr and 7% Fe, it has excellent
corrosion resistance from cryogenic to high
temperatures. Temperature
limit: 2000° F (1100° C).
Approximate Hardness: 150 HB.

TITANIUM
Metal with excellent corrosion properties in elevated
temperatures, oxidant service, Nitric acid and
caustic solutions.
Temperature limit: 2000° F (1100° C).
Approximate Hardness: 215
HB

The anecdotal evidence is pretty huge: people that use metal for the burn tunnel and riser are experiencing failure in time.

At the same time, we are experiencing large positives when we super-insulate the burn tunnel and the riser and get even higher temperatures.

Further: the barrel is steel and the anecdotal evidence is that the barrel is fine. We think this is because the hot side is a very low oxygen environment and the cool side cools the metal very fast as is puts the heat into the room.

I guess I wanted to create this thread so that we have a place to cover this issue. And when people feel compelled to bring this up, we can post a link to this thread.

let us know how long it lasts sky. I like it

people forget that just because the hot gasses are 1500+F does not mean that the surfaces are that hot. the external temp is lower so the surface only reaches half the internal difference. so you CAN have a 1800f fire in a tube rated for 1000f depending on the external temps. This is where the conductivity of the metal is beneficial because the external temps conduct and regulate between the internal and external temps, while allowing the hot combusion to occur, which is floating is flame and gas form, not crawling the inside surfaces. thats why i dont super-insulate my cumbustion zone, because with metal, external temp conductivity is beneficial

What you are saying is true for materials resistance. We've come close to entirely overcoming this problem and using high temperatures for a few reasons, one being the cooling fins we weld on to the outside of the steel. But the big reason is because our pellets burn only in the center of the tube, and excess air is allowed to flow between the combustion zone and the steel. This allows us to use air as a sort of "live insulator" is you will. Its the same principle used on conventional stoves to keep the fire and exhaust from making contact with the glass, they let in air from under and in front of the glass hence the fire never makes contact with the glass. We do the same thing with the inside of our tubing. Down the road we will be lining our stove with Microporous insulation made of pyrogenic silica, along with great emissive insulation to reflect infrared heat back into the combustion zone. For now, however, our air was system in conjunction with cooling fins is keeping the steel from rusting. Our first prototype was made in 2013 and we see almost signs of corrosion at all. Again, designing the heater to use flowing air around the combustion and heat until it gets blasted to the op plate has worked very well for us. To put it simply, imagine trying to heat a piece of metal with a propane torch, your torch is held at a severe angle in parallel with the metal, and an air compressor is blowing air in between your torches flame and the steel. That steel will not get very hot. Also, the grate suspender is made of 304 stainless steel, which also has an air gap between it and the pellets, to shield the mild steel from the hottest area of the burn tube for the first 7 inches. In between the stainless steel and A500 steel is yet another air gap.

Airflow is key in engineering Rocket Heaters. Once we have the money to add the microporous silca insulation into the internals, all these problems will be unquestionably gone. However, we dont have the money to do that right now. Mind you this insulation is better performing than Aerogel at high temperatures and has 4 times the insulating ability as polystyrene for the same given thickness.

We will be getting third party testing data on efficiency from Missouri University of Science and Technology within just a couple weeks! Our current testing data is only for safety listing and approval for building codes and hence is almost worthless for verifying efficiency. I'm all about third party verification and S&T is one of the best science and tech university's in the midwest. This should ease everyones concerns. I will also in time once I'm not busy provide photographs of the internal fire tube, so the info at S&T will prove that our temperatures are exceptional and the photo's will speak for themselves. I'm a man of science and I'm here to prove beyond any doubt my claims as a professional are true and proven. Objective third party testing and proof is what people deserve, and we at Liberator LLC are striving to get it, even if we are on a shoestring budget.

Sky Huddleston wrote:
We will be getting third party testing data on efficiency from Missouri University of Science and Technology within just a couple weeks! Our current testing data is only for safety listing and approval for building codes and hence is almost worthless for verifying efficiency. I'm all about third party verification and S&T is one of the best science and tech university's in the midwest. This should ease everyones concerns. I will also in time once I'm not busy provide photographs of the internal fire tube, so the info at S&T will prove that our temperatures are exceptional and the photo's will speak for themselves. I'm a man of science and I'm here to prove beyond any doubt my claims as a professional are true and proven. Objective third party testing and proof is what people deserve, and we at Liberator LLC are striving to get it, even if we are on a shoestring budget.

That's great news , hopefully that will settle some people down lol It looks like a great stove and sometimes you have to prove things to convince some people i guess, but that's also good, truth and facts and such

Sky, as I see it, chances are that gas analysing will show a pretty high excess air value, probably in the range of 300% or 400%. In other words, lowest oxygen level in the exhausted gases could be as high as 15% due to the air wash systems. I do expect this will keep the efficiency down quite a bit but time will tell whether this assumption is correct or not.

wouldnt a LACK of oxygen cause a much dirtier incomplete burn - rather than abundance which is clean and helps complete burn?

Depends, more is usually better, but you can get away with using less oxygen if its a hot enough fire. Too much and it can degrade the combustion efficiency as well. I suppose the best bet would be to hook up a pure oxygen tank leading right into the combustion one. Not that such a thing is practical.

An extreme oversupply of air may cool some of the combustible gases too much for full combustion, and even if combustible flow is so well controlled that combustion is complete, there will still be a large excess of cool air diluting the heat generated and making it harder for that heat to be transmitted to the mass. A lower temperature differential means less effective heat transfer.

The electrical, magnetic and structural properties of metals can be changed through heat.....Metals are comprised of a symmetrical structure of atoms known as an allotrope. Heating the metal will displace atoms from their position and the displaced atoms form a new structure. This process is known as allotropic phase transformation. Allotropic phase transformation alters the hardness, strength and ductility of the metal.....Annealing is frequently used to soften metals including iron, steel, copper, brass and silver. The process involves heating the metal to a specific temperature then allowing it to cool slowly at a controlled rate. Annealing alters the physical and chemical properties of the metal to increase ductility and reduce hardness.

source: http://metalsupermarkets.com/blog/how-heating-metal-affects-its-properties/

When iron is heated past 1,674 degrees Fahrenheit it is able to absorb more carbon but will weaken if allowed to anneal or slowly inside the controlled core and is the opposite of hardening and tempering.

Heat alone may not corrode metal but it does weaken its molecular structure. The only obvious way to keep a burn chamber or heat riser constructed with lower temperature metals from changing its molecular structure or deteriorating is to cool it passively or actively and that may extend its life but comes at a price many Rocket Stove builders desire not to give up and one of the many reasons we seek a proper Rocket Stoves and that is burning the fuel completely as much as possible and by lowering the burn chamber and riser wall and air temperature to cooler than needed to protect the inner wall from damage hinders it potential to fully burn the combustible gasses and will allow those unconsumed gases to escape through the exhaust and degrade efficiency. The entire idea of a Proper rocket stove is to create a super heated burn tunnel where gasses can not touch a cooled metal side or ride in the injected cooled air for an extended period to escape combustion. If carbon steel is not getting hot enough to weaken that means the side are being cooled enough to allow gasses to cool and escape.

The Peter Channel does a brilliant job of injecting air only in front to mix with inferno hot air and does not interfere with higher temps because of insulation and proper burn chamber and heat riser wall temps. cooling the side walls will defeat the whole process. super heated and insulated inferno walls are needed.

What you're saying is true, however insulation is according to our scientific data secondary to the geometry of air injection. We have lines our primary burn area with Stainless Steel, which is a poor conductor and reflects radiant heat very well. There are two air gaps that shield the A500 steel from the combustion zone. Think about it like this: In a tokamak the plasma is not touching the walls for any solid material would instantly vaporize, so the scientific institutions that build them contain the plasma in the center of the chamber, and the plasma touches no surfaces. What we are doing is a somewhat similar concept. Preliminary testing from S&T already show that we are way past the efficiency of any conventional wood stove. Our fuel pellets are burning with a yellow/blue color. I've never seen any Rocket Heat on youtube that has a blue flame like a gasifier. Ours does. So yeah, me may not have the BEST stove at this time, but this is a cash strapped startup. To make the very best will cost even more money, a thousand dollar or more on top of the 1800 dollar price tag. Its like buying a Blazer or a Cadillac, there comes a point in time where the extra costs for slightly better efficiency just isn't worth the up front investment. AKA law of diminishing returns.

Our heater is already tested and listed for safety as per UL-1482, so it will cost is 8 thousand dollars for a design change, on top of the tens of thousands right now. Like I said down the road we are going to use a Silica based insulation which can withstand over 3000 C. which is more than enough for even coal burning. One quarter inch of this insulation has better insulating propertys than one inch of polystyrene But right now we cant afford that insulation, its a 15 thousand dollar minimum order. We are also going to line the insulation with Hastelloy coated stainless steel, to reflect all of radiant heat. This is what we have planned, and any stove bought now will be capable of taking our new improvements and installing them easily, so if someone buys a heater now they will already be saving money, then down the road they can invest in a liner. Once we get the cash we will literally start incorporating insulation thats superior to Aerogel at high temps, insulation that reflects 99.99% of Emissive (radient) energy back into the burn chamber, and we will shield all metal with coatings and products that are used for things like rocket nozzles and gas turbines. We are thinking about using the same type pf ceramic tiles used on the Space Shuttle down the road. They are surprisingly affordable, and are such good insulators the core of a block of the stuff can me molten at over 20 thousand F. and the corners safe to touch. I seen a live demonstration at NASA's jet propulsion laboratory. I have since contacted the company that makes the stuff, however again its a 30 thousand dollar minimum order.

Henry Ford went through a lot of designs before the Model T was perfected, and he had to sell those previous designs to get by. More startups fail from taking in too much at once rather then getting products great enough to sell.

Our Rocket Heater is not the most efficient, but it is safety tested and is still way more efficient than any conventional wood stove. For people that live in area's with building codes and are dependent one electric or some other means of heat, our heater would pay back for itself very quickly and by the time our new, better versions come out they will have already saved more than enough money to offset heir original investment in a Rocket Heater.

Sky, I want to be clear. I love the attractive look of your stove and the fact that it is UL tested puts it in another category of wood stoves and a introductory level of performance between a standard wood stove and a proper Rocket stove and will gain attention from those seeking housing code and insurable models for their homes.

If you built a Rocket stove with a high temp metal like tungsten or titanium and then insulated it I would buy one tomorrow. With all do respect keep in mind the concept and definition of the Rocket Stove is not determined by shape or sound since the J and L wood stove design has existed for hundreds of years at the least. We want to make sure the name Rocket actually has meaning. It means something at permies to burn wood at almost 100% to save the environment... It means something to all permies that we are doing our part to be as environmentally coexistent as we can. I know you are a start up and very attractive and creative people and if you saw John McDoodle he has already done the stainless steel insert thing and it will protect the carbon metal as he has shown in spades but unfortunately it cant keep the side walls hot enough to burn all the fuel and allows some escape. Johns design is a very smart and is a creative wood stove like yours and i love all your creativity.

Thank you for your support and clarification, I totally understand now where you're coming from.

Stainless Steel is not a conventional insulator. But mirror polished SS is a great reflector of heat, it has superb Emissivity properties to reflect almost all the radiant heat back into the combustion zone. Of course radiant heat is only a fraction of the heat that should ideally be insulated. This is why down the raod we are going to use a full length SS liner, and this is key here, we are going to place insulation between the Stainless Steel and mild steel tubing. The insulation we will be using is literally better than Aerogel. I dont know if you're familiar with Aerogel or not, but its literally so good people hold steel cutting torches right on the insulator which is only a 1/4" thick for a whole half hour and their hand never even gets hot. The problem with aerogel, even their high heat Pyrogel, is that at high temperatures its insulating property declines drastically. For that reason we have sourced a company that produces insulation with identical performance as Aerogel but unlike Aerogel, perlite, mineral wool, etc. it continues to perform well at high heat. That product just so happens to be Microtherm. I am very impressed with its propertys, as they point out perlite, mineral wool, ceramic, etc. all lose a lot of their insulating value and property's at high heat. Theirs does not. Here's their graph on insulation rating and thermal conductivity. This is the stuff, in combination with the great Emissive property's of Stainless Steel, will make the insulation we hope to put in our heaters among the best.

Right now however the Testing Lab would charge us 8k for a re-test due to a design change that changes how the heater burns, plus 1500 for travel expenses, plus listing fee's, board certification/approval, its a real rigmarole we had to go through. We actually had the heater tested the year of 2014 in July, then had to wait until September of 2015 for a 3k factory insepction/certification, to ensure that all heaters produced are identical, then a yearly maintenance fee" of 1500 dollars, this is all just touching the surface mind you. Coming up is EPA testing, thats 25 grand or more, and if we ever modify the stove we would have to spend another 25k in EPA re-tests, not to mention safety testing.

So as you can see, we can't really make any design changes until we make some huge sales. Not to mention our provisional patent only gives us one year of protection, then its 15k for a full patent.

All in all its gonna be about 150 to 200k just for testing and certifications.

Trust me buddy i hate code enforcement and the phony money regulation racket. its all set up to hurt the small creative guy. many blessing to your company my friend.

Well I'm glad there's someone out there that loathes the racket as much as I do, lol.

Even though our heater isn't the very best Rocket Heater out there, for people who do live in area's with building codes it gives them an option to get something thats still gonna be miles ahead of a conventional stove at a reasonable price. And by the time we come out with a newer version their old one will have more than paid for itself. I am very confident that our current design is more than sufficient for many people's current plight under building codes thus far. As of now, people needed a NRTL listed rocket heater years ago, and we've delivered on that hope. Like I said it may not be the best Rocket Heater ever made, far from it, but its the most efficient NRTL listed to UL-1482 safety specs on the market right now. And thats what important, its not the best, but its better than the rest! Anyone who buys this heater it should more than tide them over for a few years all the while pay back for itself and saving them money compared to conventional NRTL listed heaters.

have you considered other high temperature metals such as titanium or tungsten. I have seen non bulk buy titanium tubes for around $200 for a 4' long 6" ID tube and im telling ya if you build it and test it... those dang stoves will be the best on the market and higher temp than stainless steel could ever be. I would buy one. titanium or tungsten built heatriser with good insulation would rock! Now that would be a metal Rocket stove to reckon with that no one has done before!

F Styles wrote:have you considered other high temperature metals such as titanium or tungsten. I have seen non bulk buy titanium tubes for around $200 for a 4' long 6" ID tube and im telling ya if you build it and test it... those dang stoves will be the best on the market and higher temp than stainless steel could ever be. I would buy one. titanium or tungsten built heatriser with good insulation would rock! Now that would be a metal Rocket stove to reckon with that no one has done before!

Well, there are a couple problems with that. Our horizontal burn tubes are almost 2 feet long, and they are rectangular. Adding that much titanium to something would increase materials cost by almost a thousand dollars. And welding steel to titanium is nigh impossible without VERY expensive welders. And cutting the tube down to length would be nigh impossible because titanium does not cut very well at all. Tungsten costs about 300 dollars per pound, making it way more expensive than silver. Tungsten also has the same density as Gold, so it would take a lot of tungsten (by weight) to make a burn tube.

The other problem is that we cant just swap out metals like this. We have no flexibility now that we are NRTL-listed. We had to pay a "design change fee" which needed to go through a board and be approved which costed us 500 dollars. To add a single 5" strip of metal. Anything that changes gthe design significantly requires a full re-test.

Instead we are looking into several processes including plasma applied ceramic lining/coating, silica insulation, aerogel, etc. There are a lot of options we will explore in the future, we want to eventually invest in our own testing equipment and gas analyzers so we dont have to bother Dr. Smith every few months or so. But again, those things run over a thousand dollars as is. Until we get sales drummed up we wont have the money to continue to experiment and develop the technology into a commonly accepted and mainstream heating source. Its getting to the point where tomorrow Im goint to apply for a summer job to help get us by

there are other higher temp metals other than steel and may be affordable to use.

have you thought about a bolt on cooling fins? or thin ceramic square inserts that slide down inside the heat riser so an insulation sleeve can be slid down over the outside of the riser? that way it would avoid retesting by using bolt ons and upgrade purchases provided to the customer.