do NOT use metal in the core of a rocket mass heater
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- เผยแพร่เมื่อ 18 ม.ค. 2018
- richsoil.com/heat In some of my earliest videos I show building a heat riser with metal on the inside. This is a disaster for any rocket mass heater that gets good an hot. Steel is liquid at 2600 degrees F. Never use steel in the burn tunnel or heat riser. There is some debate about using steel in the wood feed. Steel, or any metal, outside the riser has been fine. A perlite and clay riser can be formed with a wood or carboard form which will be burned out later. Or a steel form that will be slid out. At the 2015 rocket mass heater innovators event, Peter van den Berg built two rocket mass heaters that fit into a barrel. We talk about metal in the core while looking inside the one he calls "Minnie Mouse". He points out that there is just a short amount of steel in the wood feed - and it is okay because it is air cooled to keep it from getting too hot. Also, a 4 inch system cannot hold as much wood as an 8 inch system so it will naturally burn cooler. Our conversation then turns to explore the vermiculite riser which is held together by stainless steel screws. There are different recipes for stainless steel and each recipe has a different melting point: about 2400 degrees to 2800 degrees. So about the same as mild steel. Then we go back to talking about high temperatures with steel. The first problem is that steel spalls at about 1300 degrees F. Steel spalling is when the steel turns a light gray color and flakes off. An alternative form of oxydizaton. It has to do with the high temperatures and levels of oxygen and carbon.
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Yes, in my first build I used steel outlined with Perlite for the riser tube and that last about a month before is crumbled to pieces. Since then I use fire brick and rebuilt the stove (and made it horizontal) with fire brick glued together for a burn tube and that has lasted me for years now.
Wow, I just came to this funny realisation. Because of this movie, I learned about Peter van den Berg and with some research I learned he's kind of a neighbour to me, about 10 minutes walking distance!! Really want to learn more from him, hopefully I'll visit him soon.
since recording this, there have been some 4 inch steel cores that have worked because the operating temperature is kept below 1300 degrees F.
How does lower temp effect emissions and effeciency?
There seem to be a few steels like INCONEL 617 that are rated from up to 1800, but could be pretty hard to source and tricky to work with.
I think the issue Paul means is that steel sucks and disipates the heat necessary to make a rocket efficient. Steel may not melt, but it does decay. I've seen risers made from two different sizes of stovepipe filled with pearlite between the layers. It worked for almost a season. The temps were not nearly as high as I get with a refractory riser.
From my observations, the hotter a rocket gets, the more efficient it becomes.... and this is why mass becomes necessary.
Next stove I build is going to be refractory, burn chamber to the top of the riser.
@Kiwihouse2005 B. Sure, why not? Only possible draw back would be the immediate cooling effect is lost or rather reduced, so I'd elevate the oven by a few inches.
Ya no $@&!
I think that's the most we've ever heard Peter say. He's such a nice guy he won't talk over anyone else. Thanks for sharing this one. :)
I think that conversation with him was over an hour. We had to whittle it down a lot to get it to fit on the dvd.
Paul seemed annoyed and brushing out what this old guys was saying...need to be open...there are more very intelligent people up there...is not all in the lab :) the white hair in his head and bear shows more days lived and more learning...and this guys seems to be the kind that test and test and test until he gets it right... open minds please :)
Peter Van den Berg is from the Netherlands and sometimes has difficulty getting his concepts across in English. Paul thought Peter was using metal to line the feed, but what Peter did was build a metal box on TOP of the feed. He has a metal plate running down the inside face of the feed which serves to siphon fresh air into the burn tunnel to increase combustion efficiency. This siphoning action draws air into the cold-air box atop the feed, cooling it and keeping the upper parts of the wood standing in the feed chamber cooler, also making the feed chamber taller to prevent smokeback. The fresh air injection plate is sacrificial...it will last a season then need replaced, mainly due to the lower edge warping from being exposed to direct radiant heat in the burn tunnel. But Peter isn't using any steel in the areas that get super hot, as he well knows it will just burn out.
The reason you see steel 'Rocket heaters' for sale is because alot of amateur welders/stovemakers want to make money, and keep trying to make RMH's out of a material (steel) they are familiar with. The steel will just burn out at these temperatures, causing the stove to fail quickly, but the manufacturer Can't make it out of firebrick or castable refractory mix, as it would just crack and crumble during shipping. You could build one out of ceramic waferboard and Kaowool that would survive shipping, but those materials are danged expensive.
If you're happy they stop explaining. If you look skeptical and questioning they keep explaining. So A/B testing reveals it's better to have a shitty attitude in these situations, unless you're OK not learning much.
new study reveals .. white hair = supreme knowledge
you seemed open enough to me. paul wanted to share the knowledge he had to make sure the other guy didnt recreate a design they had problems with.
that was my take anyways
Paul thinks he is an engineer, this man with the accent is smarter than Paul by along shot.
Hmmm... I just enlarged my feed tube from 4 3/8 to 8 inches, and I used 1/4 inch steel. With the secondary air open, I can block off the feed tube with only two 3/8 holes for air... I'm getting consistently higher temps, even with somewhat damp wood... a rocket no-no.
The only thing I'm concerned about is that my exhaust temps are too low, about 110 to 120°F.
Peter rocks... but, we all make mistakes... that's how we learn. I'm sure he's made plenty.
I've made major blunders... 2 weeks of hard work... garbage... learned a lot, and the rebound from this disaster was successful beyond my imagination....
I love all this innovation, experimentation. Can't wait for my next build to be completed. So many ideas.
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Hi paul at around 830 you mention a light grey rust or scale , if you watch forging videos you will see the same stuff coming off the red hot steel , basically another form of oxidised steel
Hi Paul, Thank you for an informative video of your discussion with Peter. Great questions and great answers from a really thorough thinker. I like Peters polite oh.. oh.. oh... before correcting the argument.
I make little 500g 'Rockety' tent stoves that are all metal! (Not Rocket, but a little in common and I call them inverted J-burners). They have; inverted stick burner/fuel tube, little mass, no formal heat riser (just wasteful long flue pipe for the strong draft). The burn is very clean and hot est. 1,000-1,200C even with wet wood. They run on excess air/oxygen for very clean burning and the metal at the bottom of the burn/fuel tube is slowly burnt out as you discuss with Peter.
I have also speculated that it is the radiant heat from the charcoal+ insulation and I add oxygen+absense of carbon from smoke as a contributor to the damage. It was nice to hear someone else (Peter) state this. I use the term of; "Smoke protecting high-temperature metal form oxidation?"
I have another burn out point where the hot flue gas (often flaming) enters the flue pipe turbulently at the start of the pipe. Only about 50mm get burnt. I have been cutting it off after many hours of use. Now I use a sacrificial guard tube to address the problem. I suggest that turbulence is also another factor that increases metal decay. I think it enables the oxygen to get at the metal to do the damage before laminar flow settles in and provides some protection as well as a fine coating of carbon. Inside the fire bowl of my stove, there is a flame guide or baffle that gets 'hammered' with charcoal combustion on one side and gas flame on the other and no contact with the outside world to reject any heat. Even with all this, it survives better than the tip of the burner tube. I speculate that it is because it is bathed in carbon-rich smoke that it survives so well. It would be nice to know if my explanation makes any sense to the experts.
Sorry for my rant, but it was so good to hear someone describing what I have experience in my stove design. I am not a lone voice any more.
Here is a link to my redhot KISS Stove; timtinker.com/the-kiss-tent-stove-for-alpine-tent-heating/.
It might be inefficient, but it is delightfully hot in a little winter tent.
Thanks again, Tim
I imagine the shape - square corners - makes more turbulence.
I've never heard of the "low-carbon air" issue, at all. I never thought it was the carbon breaking its bonds that caused the spalling. Perhaps cast iron would be a better choice for the metal parts.
@@harrymills2770
Hi Harry, Yes, I find sharp corners make more turbulence whic causes better air/wood gas mixing and more complete combustion.
Cast iron would be better, but not in my backpack as I go off on a ski trip!
I was not suggesting that the carbon was causing the spalling I was suggesting that the excess carbon in the flame or on stove surfaces can provide some oxidation protection for the metal because it can mop up the excess oxygen that would otherwise be left to attack the hot metal surface. (Peter starts to talk about this at about 6 min into the video). For me, it is a compromise between stove efficiency (wasting a little bit of smoke) and having that smoke improve the longevity of the very light all-steel tent stove by reducing spalling. Tim
I only knew metal wouldn't last, not why. I've watched dozens of videos and this is the first that goes into the metallurgy. Very interesting, thanks.
Cast iron and carbon steel withstand high temperatures.
Transmutation
I made a steel core, but I agree with the makers from this video. Steel is easy to use and cheap to get but it's just not the right material for an inner core if you want this type of heater to work as it should.
For me it was more of a learning project, and I only use it outside in the summer if I want to sit outside a bit longer.
I don't have an opinion, I'm still learning. This was informative, thank you.
My rocket's wood feed is of 1/4 inch steel. Where it is closest to the burn tunnel (hottest part), it is distorting...
If I was to make another, I'd use hard fire brick...
Most of this I agree with, however... I've made about 500 rocket stoves using steel, in the core and the body, and have no issues because I use the correct kind of steel according to the temperatures involved. SS310 is rated for use at 1150C (2100F) and so far I have not seen any kind of spalling or oxidation on the cores I've had in homes over the last Himalayan winter getting about 12 hours of up / down firing every day for months at a time. Not to say its the best material out there... I just like it due to being more portable than ceramic cores. Having said that, I would probably choose a ceramic core if it was practical.
I need a bit of clarity on your statement. You say rocket stove. Maybe you mean rocket mass heater? I only mention this because .... th-cam.com/video/IAb3922HD9U/w-d-xo.html
Yes its a common point of confusion, even here in India. I use the word 'stove' as there is no universal word for what I do... its like a rocket mass heater, except without the mass. I use a rocket core combined with bell effect to maximise heat radiance into the room, so I guess I could simply call it a Rocket Heater, but that doesn't mean much to the people I'm reaching who have no idea what a 'rocket' has to do with heating their home. We are starting to look at ways to add small amounts of heat storage mass, such as water mass in this example: th-cam.com/video/tE4j5QS1Ni8/w-d-xo.html
If you want an easier to transport option for a riser, Pinhead from donkey32.proboards.com uses a ceramic fiber blanket inside a metal flue pipe, which is easy to make, light, and people say it works well: facebook.com/photo.php?fbid=10154992096951974&l=3e4ec1844f is the link Pinhead posted for a picture of it from above. Pinhead calls it the 5 minute riser on proboards.
So after watching this I'm wondering it is possible to build a batch box RMH out of an old Fischer type woodstove? My plan was to line the entire burn box with firebrick. I would have to buy longer bricks and just run them across the top from side to side resting on the side bricks. Should I poo poo the plan? The entire inside would be lined with fire brick except for the door. I was think of welding the rise on the top of the stove. Would it be safe just to line the inside with clay?
In this video, ernie kinda does what you are suggesting
th-cam.com/video/DMUES-34Ioc/w-d-xo.html
Cool thank you for making a video about this to give us a better explanation of why. Very interesting. It's kinda cool to see RMH tech evolving as you all experiment more with different design and materials for better efficiency.
I expanded ny burn chamber to take cord wood from 5 3/8 to 8 square. I used 1/4 inch steel... it works but crazy shit goes on... getting it to draw is now a challenge, whereas before, it was much less of an issue.
Thanks for your input. Makes sense.
Still going to use the stove as-is this fall, but stove 2.0 is on the drawing board, using Peter's burn chamber... what is beyond it is still going through design permutations.
So many ideas....
T.W.: No need to re-invent the rocket stove. Go to Aprovecho Center, "tier 4", TLUD style stove by Kirk Harris.
was going to buy the eco-zoo stove but it is made of metal, I have a house that used to be a stage coach station, I salvaged the chimney bricks and 4" x 30" ceramic stove connector tube, thinking of taking 5 gallon bucket and using the tube as chimney and using chimney bricks as burn chamber , enclosed in perlite and concrete, is this my best option?
Bruce, the response to this is more than what will fit in a youtube comment. Have you watched the DVDs? Have you posted to the forums at permies?
Its not the dark color of the steel, its the energy density (ability to accept thermal energy). Also, galvanized steel has a much higher thermal conductivity (ability to lose thermal energy) than normal steel.
I appreciate all of the research and development here with you folks, especially with pyrotechnology being so utterly innate to human interest, coming right after our discovery of sticks and stones, and now, finally the thought, let's just not burn the wood, but the gasses, and hydro carbons emitted from the fire. I wonder why RMH are not fully burning soot, especially with soot having such a low burn temperature. Maybe because it is not spending enough time in the burning chamber, but your guess is as good as mine. Just another mechanical wrinkle to hammer out. I can see why you do not have a lot of room for aesthetic considerations yet while still trying to perfect the burn itself. I wonder if one of these could not just be fed with propane or gas, or at least as a secondary automated system, especially helpful if one were really laid up. Lots to keep you busy. Don't spend a dull moment.
what the old man is saying, is indeed correct: heating steel in an oxidizing flame, pulls the carbon out of the steel. It's not rusting indeed, because that would mean binding the iron of the steel with the oxygen.. which happens also, but slower than the carbon degradation of the steel. When the carbon is gone, the rust will become the problem, because the oxygen has no carbon to bind to anymore. That's why you see a phased approach with steel, when it goes wrong. It is the difference between what is known as an oxidising flame and a carbonising flame, something which is well known by steel welders who use gas: you need to regulate the mix of gasses correctly, or else you will see a sooth-depositing, carbonizing flame (which can also be useful for certain purposes, btw. e.g. when you want to deposit some sooth as a protective layer onto something, for some reason.. so it isn't all bad. For welding, you want it clean, of course.). Now, you could get creative, and inject some carbon at the spot where the flame has the danger of becoming oxidising, so that the steel gets attacked less at that spot, if you have no choice than to use steel at a certain point. The carbon will actually form a protective layer on the steel, and if the steel is cooled well enough, it won't melt either. Ventilated cooling fins on a piece of steel in this way might be an idea. This will then of course give a more sooth-depositing flame at that spot, but if the burning temperature is high enough, and if there is enough oxygen still left down the path of the burning chamber, the carbon-particles-loaded smoke will after-burn into a purer CO2-mix, and show up as no visible smoke at the exhaust.. just hot CO2 without actual carbon particles. It's all about finding the equilibrium between heat and the melting of the steel (or rather: dissipating the heat away from the steel), if you can't do without the steel, and having a non-oxidizing flame (=carbonizing) where there might be steel, getting your burn chamber hot enough (preferably in a ceramic material), after-burning your smoke, etc. It's rocket-stove science! lol
What about using a stainless steel keg in place of the iron 55gal. Drum?
stainless should work for the outside
Hi. Does anyone have insight into using metal inside a refractory casting, like a rebar or finer mesh to add strength to the mix?
Matt Walker has cast a riser using fine stainless steel needles mixed in...rebar or anything thick would expand/contract too much and crack the fired riser.
I would reinforce the refractory with fiberglass.
so whats the verdict on his design? is it predicted to be ok? any follow up to see if it lasted?
I think the answer is: part of the feed tube, if you allow air around it to cool it off, should be ok. or to put it another way: it's possible to use steel in places if you're super careful and knowledgeable in metallurgy, but it's probably not worth trying since high-temp masonry is easier and just works.
Paul, is it feasible to use a chimney terracotta flue pipe for the heat riser?
I bought some once to try and ended up never trying it. I would want to look up what temperatures it can cope with first. And, if I did try, it would be wrapped in durablanket.
I will gather that information for future reference Paul. I am encouraged by your site, knowledge, and reply. Thank you
We did try them a few times. They tend to crack pretty badly, pretty soon. Best advice from another mason: to get a little more life out of them is to make a long cut with a masonry saw, down one side, so they are "pre-cracked" and maybe the heat stress won't make more destructive cracks. However I doubt this would save them in the heat riser. There are some higher-temperature ceramic castings of similar shapes available in Europe called "Chamotte" or "Schamott" that are more like fire brick in their ability to withstand the heat. Possibly a US fire brick manufacturer or importer could find you something like that.
Thank you kindly
To be economical (aren't we all?) I suggest going with aircrete.
What I've learned from this is that as long as the steel is not getting red, you are in no immediate danger. It can get some red, 900F and not spall. But if it's getting bright red, 1300F, then you're in spalling danger.
For those who insist on using metal, they need to go with Inconel. If you do so, give the drawing to a shop equipped to work with it. It's too hard to drill, cut and weld for Home depot equipment.
santa called he wants his sweater back
If wood has a potential thermal energy then it wouldn’t matter how much wood you are using if you are reaching or about reaching its potential energy
Paul I have been a big supporter of your work for years, so please don’t take this as a personal attack (it’s sad I need to preface with this but it is the age of the interweb) but as long as I didn’t misunderstand your point, I don’t buy this claim at all. Wood will not melt steel in a forced-blast furnace, and it won’t here either. But, reduction or oxidization might be eroding thin walled metal liners fairly quickly. I would bet my life and my house on this as I say this from experience, not armchair opinions. I love your work, even the stuff I don’t agree with, keep it up.
check out the melted cored on the web4deb channel. This is not speculation. This is dozens of melted cores.
I checked out the autopsy video on on web4deb channel and didn't see melting. I did see total failure from oxidation. Basically the iron is converted to brittle flakey millscale. This happens at temps far below melting temp like in a forge. Are you seeing evidence that the steel has actually gone fluid?
Has anyone ever stuck a thermocouple into the hottest part of a rocket stove? I'm curious if there's any hard data. Maybe temperature cones like potters use in their kilns would work?
I'm in agreement with the basic point, though. When you see stainless grates rust out in a barbecue, it's clear that regular exposure to far higher temps is a bad idea.
yes, we have done some cone testing. At the same time, we have experienced different things melting (like perlite) which gives us a good idea of the temperatures we are reaching.
Steel or metal rocket stoves are an endless pain, there is no need to use any metal at all
Finally, someonewho gets it. CLAY
I rather make a rocket stove out of lightweight concrete.
How do i buy and get this?
richsoil.com/wood-heat.jsp
Hello Paul .. I have an empty open Oxyacetalene bottle what about using one of these for the riser?
what is the word you keep using, "the steel will "spall" not melt" How is this word spelled and what does it mean?
I thought we covered it pretty well in the video. For steel it is because of the carbon in the steel. It sorta flakes off as a form of oxidization. It turns gray and flaky. This is why you have "cast iron" stoves instead of steel. Cast iron is pure iron. It doesn't spall because it doesn't have the carbon in it like steel does. en.wikipedia.org/wiki/Spall
paul wheaton Why not make a rocket stove out of cast iron then?
Take hightemp mortar coat steal then wrap thst fire blanket that the exterior hardens when you use activater turns outside like fiberglass. Bamn
Where are the instructions for an all clay rmh?
I have never heard of anybody trying that. Perhaps you will be the first?
paul wheaton this is why you don't late night obsess over rmh videos! I thought that's what you were saying to do but I watched again and understand now lol
If you can find cast iron that will work for your design it will last a looonnnngg time.
Cast Iron naturally contains carbon in the form of graphite.
I would guess that pure Fe would still oxidize as well.
Ceramics (Clay) are often pre oxidized.
I only just found out that the ash in burnt Anthracite is Silica oxide, Aluminum oxide and Calcium oxide.
This is all TH-cam learning so you might want to fact check it all :]
Cast iron would easily tolerate the heat without damage. But I wonder if it would absorb too much heat for too long in the beginning of the burn? The rmh needs to be a quick hot burn from the get go or you have too much incomplete combustion.
Crap. I just finished my 8 inch system with a 1/4 inch steel riser.
At least you can get that steel back now.
Your efft bro
Oops
7:00 Sprawling happens at about 700 C
I want to buy the videos, but I have a question. Do you give actual build plans, with materials specified, and also dimensions clearly specified? I have wasted money on books that are full of pictures and very little to zero actual facts.
Things like, "we have tried this design, and it was inferior to this design" would also be helpful.
So, before I pay money for videos, do they contain real build information with real dimensions etc?
There are actual plans for a lot of this that are sold separately. I know that for the wood box shippable core, we do share dimensions. I think there is a lot of exploration on what works and what does not.
@@paulwheaton Thanks Brother.
We are purchasing acreage, and will be building. Have you ever heard of someone running the exhaust through a concrete floor? I have seen radiant floor heating using heated air, but I am wondering about using the heater's exhaust. It would be very long, and so maybe a fan at the exhaust end pulling air through until it gets to drawing on it's own?
@@jaycoy59 Lots of people have used a floor as the mass - yes.
Use cast iron plumbing soil line for the riser. How hard was that?
have you all seen rocket mass heaters with metal in the core? On the interwebs?
what is the melting point of pumice?
Paul, why not try to be less eager to make your point and instead just ask Peter and help him express himself in English by listening and summarizing? Your clips would be made much clearer and accessible. You message is worth it.
Erik, I do not understand what you are suggesting. Perhaps you need to pop out to the netherlands and make the videos that you think would be better.
Erik: It looked to me like Paul was extremely patient and respectful. These men have a lot to offer and the language barrier slows it down. Paul is "eager" to understand Peter/learn. His mind is going way faster than either of them can talk, even without the barrier.
why would you us steel when the correct way of building rocket mass heaters is out of fire bricks and cob
What about the liberator? Wer buying one because it makes our insurance agent happy.
liberator has insulation inside the metal. Plus, being just 4 inches, it doesn't get as hot.
@@paulwheaton thank you. I hadn't noticed on the factory tour video.
The old Gen 1 didn't have insulation and used cooling fins. That made the heater less efficient overall. And the 4" core reduces peak temperatures due to the square-cube law. We've long since switched over to using refractory insulation on the combustion chamber, with a steel outer shell for strength.
@@liberatorrocketheaters834 awesome to know. We really like your heater and are excited to order, we almost have enough saved up.
We are all just trying to learn :)
What about stainless steel. Won't stainless steel last a long time. Yes. it will cost more but this is for an investment so who cares how much it costs if it lasts 30 years.
Stainless melts at 2800 degrees
yes..........Liberator???????????!!!!!!!!!!!!!!
Use stainless steel.The ,,metal,, dont last not because its corroded.
No wonder stainless steel containers make good crucibles for hobbyist metalcasters. Doesn't rust when trying to cast aluminum or copper.
Steam locomotives burned coal, which has a much higher BTU than wood, and were constructed entirely of steel, yet they seemed to be quite sturdy all through their service lives. Somebody's figures are off.
Basically the steam combustion chamber was made of several layers of sheets of metal. The fires were lit in the main chamber. The outlying sheets were separated and filled with water so as to create steam. As long as the boiler was completely filled with water, no damage would result to the inner metal layer. It was the boiler man who was responsible to make sure that the water levels were constant as the steam was released.
SS 444 would also be preferred