Just finished! And to be honest after I was done, I said never again lol. Digging clay and mixing it by hand was not fun. Then I fired it up, and I love it. Couldn't have done it with out you're help, thanks!
Thank you so much for sharing all your expertise! I just watched your sourcing video, as well as many others! I am in Mexico, sourcing is a big deal as the cheapest thing is always reused here ( which, basically, is a good thing…just making it harder to find!!!) . I love the idea of the cast, I didn’t find a plan or instructions so I am not sure yet to what will get into my own soon . Bricks are definitely very cheap here, though fire bricks will be a killer. 😅 Things to consider: shipping for me: no company can ship directly to my place (no address, only a gps location and the looong Camino makes it impossible), so I will have everything that will be shipped, to a friend in the closest city. I am a woman, I had a brain injury so I don’t have your strength anymore guys 😉. The maximum I have been able to carry and install are solar panels. For that reason I am planning with the smallest pieces I can. My questions (or do you have videos answering all these questions ). I will keep going and watch 1/do you have specific videos on plans for the core? 2/What matériel goes in? 3/Can we buy doors by itself? I plan to build it in a wood cabin (working on the plans now: I will build a maconery part to support the weight on that part, my understanding is that it is safe with the fire, am I correct? ) PS , I am in the mountain just up to a subtropical climat. Sounds weird to build a mass stove in subtropical climat…I know…though mountains are coooold in winter and still extremely humid. Without heating I have mold ( and mold+ neurological issues= big no no)…
Lol I was trying to read the dimensions off my phone, but i took out the laptop and its much better, also appreciate the effort put into having the exact measurements scrolling along the bottom, thanks!
I just subscribed today. I really appreciate the rocket stove videos. They are wonderful teaching devices and I feel a lot more confident about attempting building one. Thanks so much for sharing this information. You are an excellent teacher. Loved the huglekulture video as well.
Thanks for the heads up, totally see what u mean. I was already thinking that several tiny cracks could prevent one huge crack. Just all part of settlement and transition from hot to cold. Right on man thanks!!!!!
Right on. I think I get it!!! Bigger is better because the corners cause drag....thus reducing the area of free flow.. Whether it be at the riser top,barrel sides or bottom manifold....thanks alot bro
I do thank you for your patience with me in my misunderstanding. NOW you are perfectly clear... Again, for my part in not understanding... Please forgive... I just want to make sure that I proceed and don create a problem... so AGAIN... Thank you for your patients and willingness to explain... Respectfully, bob P,S, YOU HAVE DONE A GREAT JOB IN YOUR PART OF EXPLAINING YOURSELF AND THE PRINCIPALS...
Thanks again for this inspiring video! I made the mold box yesterday (out of wood, not hardibacker.) Today I did some research into the materials. (continued in next comment)
This is brilliant. Love what your doing with the technology. In some sense, these cast models could be used as the basis for a small scale production business. Thanks for documenting and sharing!
Sounds great man, I will defiantly go 2 in thick on burn chamber. luckily iv got refractory to burn!!! Pardon the pun. Thanks a million bro I feel tons better about it now. This is my first build and it's in my shop. But I'm taking it slow trying to research and absorbe all info possible. Thanks again for your time and advice. I'll let u know how she turns out!!!
Curtis Webb Cool man, so glad to help. One thing I should mention, and it's not a problem at all but you should mentally prepare for it since it trips many people up. The reason to surround the whole thing with the clay/perlite inside the brick surround(in addition to being crucial insulation) is to isolate the whole thing from moving, so it doesn't make a damn bit of difference if (when) it develops cracks. In other words, it's probably going to crack at some point. It doesn't matter, at all. Do not freak out! That's what all the stuff around it is for, and why it's referred to as a "core" rather than a stove. The temperature changes so greatly and rapidly so often, and differently in different parts of the core, that it's just going to happen at some point. Just thought I'd let you know, so many people can only see a crack and think "fail", but if you accept it as part of the build it will have absolutely no effect on performance or longevity. Just thought I'd let you know! Good luck man.
Great job with this design; I like the idea of precast to using bricks, also great job with providing the information of your build. I am dissatisfied with my “J” tube build, but was looking for a light weight-portable unit with a bit different use. I also have looked at using fiberglass matt as an outer skin to the Kaowool insulation dripped in ceramic slurry the test did quite well. I believe I will look into the next tube build alone these lines as you have shown. Thanks for posting.
Nice work! I like your ideas and solutions. Understanding the requirements and risks, plan with some margin for error, and test the stuff before you install it. Good practice!
milled glass fibers are available ,used in FRP mold making would help homogonize the mixture. you are quite capable at taking a basic design and streamlining production and adapting it for more versatile applications. well done and continued success.thanks for demystifying the inner workings.
Thanks , the way I was thinking was to put the feed outside and go threw the wall with a J tube and that way the barrel will be inside that way I will get the heat off of that also .
Well, I made my casting yesterday. Using the amounts of fireclay, fire cement pearlite and fiberglass that you recommended only filled the form up to the top of the burn tube. I had to slip clay bricks in the sides for filler and mix up a bag of quickrete and vermiculite to top it off. I hope the thing holds together. I think I should let it air dry a bit longer before firing it up. I used concrete/verm. for the chimney also.
It is doable, i think. It will crack a lot most probably but we dont mind that until it holds together. So i recommend to put some reinforcements inside. Like reinforced concrete, but with long glass stripes. Painters have tape like (thin veil or tissue like) material for dry wall joints. We could use that to keep the piece from cracking, (or at least not to fall apart) by placing the stripes near the surfaces of the piece.
Unless your house is so tight you can take it into space, I wouldn't have thought it was a problem, the negative pressure will find any leaks, there are always some, even in the best built homes and it's not just doors and windows but roof and walls as well, although your walls will probably be pretty good but you get the idea.
Thanks for the info, I like the cast J tube a lot better then fire bricks.Thinking about some bolts imbedded in the area where the riser goes to anchor the riser to the J tube, when the rise is also cast like you commented about.
So we were on a ski trip over weekend and we lite a fire in fireplace and that darn fire didn't last long I woke up saw it was out tried lighting it again but nothing . Wish there was a rocketstove there lol . I gotta get motivated one of these days and make a core lol
broaudio just so you know rounding the top of your feed chamber is a no no if you are burning larger sized wood. that clean sharp edge helps brake the fire from climbing upward on your fuel. like your mix. I gotin away from using fire clay.. Iam using small amount of Portland & feed clay (from feed store),perlite & mix thick then add cat liter(low moister at this point). This insulation mix is so good I ran the exhaust under my burn chamber & bench so I can load while sitting on it .
Suggestions for the cheap asses like me: Use fire clay and silica sand for the insulation mix. 2 parts sand to 1 part clay, mix like the video shows. Very cheap. This is used in to make small charcoal foundries for melting aluminum and holds up well. MUCH cheaper than premix refractory cement. Makes a good crack patch compound too. You can also add some small wires (chicken wire, coat hangers, etc) for "rebar" to add strength and help prevent cracking.
Broaudio, Really nice and simple explanation...thank you. Just a couple of questions: >is the finished inside dimension of the core (using 1/2" OSB) to be 6" square for a 6" system AFTER the wood burns out or 5 3/8" square (as you indicate to Mark) AFTER the wood burns out? >Also, in your other videos you show one of your stoves with a viewing window/air supply, how long should that tunnel be before the burn tube begins?
I think I'm finally settled in now and HOPEFULLY start my build of the cast core RMH. I have two questions: (1) I always thought that concrete (including refractory motor) needed TIME (the more time the better) to cure VERY HARD (which is what I want. Yet, with your build, according to you, "I lite a fire the next day and let it rip"... My question is: "will my cast core build be harder and stronger if I were to let the pour set up (Without heat) for a couple of weeks before actually liting it up for the first time. My second question is about 'the proportions' of clay/perlite (1:1; and/or 14 parts of each PLUS whatever amount of refractory mortor, I can afford. My question is: "Approximately how many 50 lb bags of clay did you end up using to build both the stove AND the riser? ( I'm guessing, what, about 150 LBS of clay and equal amounts of perlite (via the suggested ratios????? I appreciate that your very busy but I would really like some idea before I proceed (Hopefully this week (before the cold sets in)
+Bob johnson Bob, if you want a hard cast core, you don't want to use this mix. This one makes a soft, insulated "liner" for a cob surround. I can tell by your question that you won't be satisfied with it, and it will crack. I recommend finding a commercial castable refractory if what you want is concrete-like performance. If you do go this route, your estimate is about right, 150 lbs of clay and an equal volume of Perlite. Good luck on your build!
Preaty cool idea on the rifleing designs using a rope in the casting BUT broaudio is right it will just create drag I'm afraid. Iv been studying the laminar flow effect, yall should check it if your unfamiliar with it. It's fluid dynamics, basically it sez the layer of air closest to the rough brick surface inside the system allmost stalls, causing the layers of air above it to tumble or mix!!! Lots of fluid dynamics going on inside these things.....
Was wondering about the "MASS" you used for your Rocket Mass Heater? Which materials are best. Was thinking of using rocks and stones found on site (on my property that I would dig up... (2-10 inchs in size. Would that work? I just have a limited amount of 'COB" (clay) hence wanted to use larger ROCKS (10 inches ini size) for the mass. I would use the COB to act like motor to hold it all together. Your thoughts please.
Bob, that's a great way to go. Rocks are better mass, but are tough to couple effectively. If you seat them all in cob and make sure there are no air gaps, you'll have the best of both worlds. Monolithic and relatively high mass. Good luck on your build, thanks for the comment.
I have played with cob alittle last summer now, and had a blast, was hoping to make an all natural version, would the sand / clay / straw mix not hold up in a RMH outdoor kitchen application?
Did you see any damage to the wood around the core from burning it? I wanted to put one of these in my home.it would rest on wood floor I am trying to figur out if the core or any part can get hot enough to cause my floor to catch fire.
Hi Matt! have just finished my own outdoor half barrel firebox with 20 ft heated bench in a c shape. having my first party around it this Friday evening. Thanks for the tips and inspiration. Pics to follow. I want to cast an 8 inch batch box with a window on one side. Do you have any suggestions?
Great build! Love the stuff you are doing with rocket stoves and your designs have given me some inspiration on what I can do when I start building in the spring. Two questions: As to adding the fiberglass, would polypropylene fibers (fibermesh) work? Would even less water in the mix be possible and keep it from cracking as much? Thanks for taking the time to make and post the vids!
was looking into making my first rocket stove i am going to be using it to heat a h homemade hot tub outside wich will make for a good trial situation and i love your idea i was wondering what u would think about my idea of making the internal core out of firebrick and casting the same mixture you are using aroundthe brick i am thinking this will add a tremendous amount of insualtion value. I live in maine the ground is almost thawed enough to start construction and will be posting a video soon
Hi,I am investigating a iron rocket stove insulated with 2m3 of sand. I like to create a sandbattery with this. Anybody any idea if the iron will melt or will be deformed.? Insulation is not preferred because I like the sand to become hot. Any suggestions are highly appreciated.
Hmm that makes sense with the air gap, but is that layer if perlite before the durock below the brick tunnel supposed to be structural? Like one would just make a level layer if clayperlite and put on durock and build the burn tunnel? Thanks!
Great work, thanks so much for sharing. Looking forward to the riser construction video. Have you experimented with the shape of the poured burn chamber to make it more rounded on the internal square corners? Do you think this would make any difference? peace ~//~
Can I use castable refactory cement? It is a dry mix, not the premix. Also you said in the video to use as much as you can afford, so would it be stronger to put two buckets of the castable cement to one bag of clay, or would that just be a waste of money?
Maybe as a good idea for nex projects: Use with some safety precautions water (yes water) as the mass. There is no comparable good substance to store heat such as water . (you can do your own research -> heat capacity per kilo) For comparison> 1 (!) Kilo of water stores more heat (at 99°C) and at the same temperature than: - 4.5 kg aluminum - 9 kg iron - 11(!) kg of copper or - 5,8 kg asphalt - 5 kg Solid brick - 4,2 kg calcareous sandstone 1 - 4,7 kg concrete Even if you bring 1 kilo of aluminum to 350-400 ° C, 1 liter / kilo of water (with 99°C) still stores more heatenergy than the kilo of aluminum. (purely to the understanding) And water is a lot cheaper than the mentioned materials^^ If you take a thermostat from the automotive sector (92-95 ° C) and a large IBC container, you have the cheapest and most efficient heat storage. Which can not overcook so quickly (1000 liters of water need "some" time) Should it come that far, we have the thermostat that can push away from the heat source ;)
I have and idea that would help to create a vortex within the flue. Wrap hemp rope helically around a 6 inch PVC pipe inside form like rifling inside a gun. Cast the refractory material around the hemp rope. When the cast of refractory has solidified for a day, withdraw the PVC pipe, leaving the rope in place. On the first burn the hemp rope will be consumed, leaving a nice helical twist within the inside diameter of the stack. What do you think?
Curtis Turner Hi Curtis, no need, it will only add drag where you really don't want any. Don't over think it, the J design is deceptively simple yet achieves complete combustion very effectively. You really can't make the burn much better. You'll get better results focusing on good insulation and sealing of the core, and good flow through the whole system. Good luck on your build!
Thanks for reply. Learning a lot. So if you want a front window like you have in your home, should you plan for it in the core stage, or just cut it out later?
need to make a water heat. can you replace the mould with insulating ceramic fibre board and no need to mould using fire cement mixture. need a super hot flame coming out of the riser, to heat a 44 gallon water tank held above.thanks
Looking at the video, you used fiberglass matt for insulation, right? How much did you need? In the video you jumped from the fiberglass matt all shreaded up, to the photo of mixing the pearlite and fire clay. The fiberglass is not used there, right?
Hey, sorry I missed this. RUclips is sorta awkward for communicating well, I do try to reply as quickly as I can. I used a couple square feet probably, all shredded. And yes, I mixed it into the perlite and fireclay. It's not necessary, but gives a little better tensile strength to the mix.
Brian Beck Brian, it's just regular fiberglass. It most likely burns/melts away in the inner layers, but should give some strength to the outer. It also allows linear clay structures to form along the length of the fiber, increasing tensile strength. You can google fiberglass in ceramics and find out more about how it's used there. It's similar here.
I must not have been clear. do I leave the fiberglass into the bottom of the 16 X 16 X 32 box as well as on top box OR do I shread the fiberglass into 'wispie bitt' (without additional fiberglass batts on the bottom and top ? (i.e.) I THINK you're saying "Shread up a bunch of fiberglass (don't leave it in batts????
I am actually building a rocket mass heater for my hoophouse right now. I am getting a lot of smoke back out the feed tube. I like this design. I have a question regarding the riser tube. If I am using 8" tube, should I just use 2 - 8 inch tubes screwed together to make a 16" tube and insulate between the inner and outer? I considered using your steel half barrel design, but there will be a lot of water in the hoophouse and thought it would rust out. Thank you for your videos. Much apprec
Thanks for the reply! I gave that book a couple reads, and I did notice a section on building on wooden floors. I just really understand it. Have you done an install on a regular floored home? I am putting mine in a insulated shipping container and I can't wrap my head around what to put underneath the combustion chamber. Right now the floor is Aluminum T channels, then 5/8 plywood on top. I am going to use Roxul, but I need a subfloor, but then won't the wood just catch on fire?
Dude, you're the best- I've been looking for something like this and I was getting a headache, tryin to figure out measurements and proportions (and motivations) out of all the piecemeal info out there, about RMHs! And it seems everyone is using fire brick but it's not much of an insulator. Your way, I can pour a hybrid aircrete mixture (cellular concrete with basalt/ fiberglass and/ or vermiculite) and have a core that's superior in insulation and very LIGHT. And with aircrete, I can cut out my cleanouts easily with a wood saw. Instead of flue vent distribution, I'm going with bell courses. Thank you! Any insight you have regarding my plans would, of course be much appreciated.
You are welcome, thanks for the kind words. I think you have a good handle on things. Portland based cements won't handle the temps in the core combustion areas for long, but you could probably run it for a while before it deteriorated too much. If you want it to be a forever build, I wouldn't recommend it, but as a first build or a step in a progression, I think it's probably great. Hope that helps.
Yes; then perhaps I should try aerating fire clay and my fiber additive (with or w/o fireplace mortar) for the pour into the core mold... do you think I'll have to burn-cure this afterwards? My preference is to cast a light core that I can easily lift but that will not need repair or replacement down the road. I suppose it's time to run some experiments and for what it's worth, I'll let you know what I discover. Thanks so much for sharing your ideas and perspective.
Getting closer to casting - wondering if one were to scale this down, say to a 4" outlet, would it be to much to assume that I could just cut my dimensions for the pieces in half??? The shop is only about 400 sq ft. Thanks
Richard, you may be able to, but 4" systems tend to be very tricky to get right, and are a pain in the butt to feed in my experience. I'd recommend no smaller than 6", you can feed less wood if you don't need the full output. For a 6" system make the square passageways 5 3/8" square or so, and leave the overall lengths and height of all outside dimensions the same. A big pitfall of scaling down is you can leave yourself with no room for the riser/barrel combo if you shorten the overall length by too much. Good luck on the build, and thanks for the comment.
Do you have any idea approx. how much fiberglass insulation you used (in your mix? I am confused because first you show your marking the box with 4 inch of fiberglass and then shreaded or tore up the fiberglass for the mix. DO I DO BOTH.(leave a 4' mat all around). or just enough fiberglass (eventually torn up) and mixed in with the clay. perlite and fire cement?
Nice job ! How are you ? I would like to know if you ever had any ideas for heating water for a radiant heat ? I have a sand blast shop ,it 18 by 40 and I installed the tubing in the cement floor . I can not have a flame inside because of the big fan to suck out the dust , so it's hard to heat . But early just want to take the chill out ! Any ideas , I have built a Gasifier so I'm a little familiar with this but always looking for good ideas . Thanks and like all your videos .
At the end you say, "then you're ready to fire 'er up". But presumably you would need to connect it to an exhaust pipe before burning, correct? Or are you moving this whole core and burn chamber into place in the house AFTER you finish constructing the core components?
The latter. I build them outdoors, or, rather, in my wide open shop, and then burn it dry before moving inside. You could cast in place, and connect the exhaust first, then dry it out in place. I actually think this is a better way to go, but in the case of the video I was building it for a friend, so was working remotely from the final install site. Hope that helps.
I don't think I could put a time on it, but the idea is to get it firm enough that you can move it without it sagging or deforming. I would say that a few(4?) hours of burning will certainly not dry it entirely, but should set the mix so you can move it safely. Once in place you can start cobbing around it even if it is not fully cured. Thanks for the comment.
How is the cast core holding up? This looks like the best way to build a stable reaction chamber provided the materials are working well. I was contemplating pouring a ceramic core because of it's resistance to heat, but I don't know if that is possible or if it would work..
Hello broaudio. Much respect. I like your cast core instructions better than most I have seen on RUclips. My question is I have a high quality industrial dry refractory mix. Rather large amount came my way by luck. I read in the comments that this type of refractory is not a good substitute for the gallon size ready mix stuff that contains sodium silicate . so my question is would I b better off casting my burn tunnel out of pure refractory cement say 1 in thick, then fill the bottom of my 16 by 16 by 32 inch outer form with fireclay perlite mixture,allow it to cure, cast my burn tunnel ,set it on the 4 inch thick perlite fireclay bottom, then complete the rest of the infill around the burn tunnel with perlite fireclay. Basicly a 1 inch thick burn tunnel or square u shape...surrounded on all sides by insulating perlite fire clay mix. By the way I constructed a 16 by16 by 32 inner dimensions box out of firebrick for a perminant ridged form, instead of using cob to surround the core. Also plan to line the brick form box with heavy duty foil shiny side up to help reflect heat back inwards and to keep the core mix from sticking to my brick. As shrinkage occurs I plan to fill the surrounding crack between firebrick box and core with sand, for support and shock or tremer resistant cushion for the core. Iv done a ton of research on RMHs and homemade and industrial refractory and feel that I have only scratched the surface. Please let me know if I'm on the right track with this idea... Thank u so much for your time and your awesome videos.
Hey, thanks for the kind words. Your plan is excellent, and is really the better way to go. My mix here is just a DIY mix for folks who can't source true castable refractory. If you have enough refractory you might up the wall thickness to around 1.5-2" just to add a bit more resistance to wood knocking around in the feed, but overall I think you will come out with an awesome stove if you build it exactly as you describe. I've done the brick surround and it's an excellent technique. Good luck!
Very informative! I'm thinking about putting one of these into a building that I'm (again planning) on making a "tiny home/cabin" and I found your video very useful. I'm going to sub you and hope to continue to learn from you over time. Quick question, do you know of a well rounded resource that I can use to learn the basics in RMS design by chance? Thanks in advance!
I'm confused. Forgive the noobish question. With a riser, could you still add an exhaust that goes runs under a bench? Are you going to add an entrance to clean out ash?
Dyer, did you mean without a riser? I'm confused too! This is part one, see my other videos for part two which is casting the riser. This stove will have a riser, and yes it can power a bench run. No ash cleanout in the core, it's a bad idea in my opinion. It's easy enough to clean out what little ash there is with a small scoop every week or so. Clean outs are very important in the flue runs under the bench, that's where most of the fly ash accumulates. Thanks for the comment.
A quick question:... I am thinking of buying 'chimney clay flue pipe' (8 inch) for the burn chamber and riser rather then the hardy board build. I would 'insulate per your recommendations to produce an insulated box. My question is will the clay flue pipe build negatively effect the efficiency, etc.
have you considered using chicken coop wire or similair for a rebar effect? maybe it would help minimize the cracking? that's what I would experiment with. thanks
What is the source of your research on the efficiency of the cast core vs built with firebricks? If a cast core is more efficient, then it must be due to the insulating characteristics of the cast material, correct?
Hi Douglas, in this video I was hoping to convey that I felt that the insulated core offers better performance, not necessarily efficiency. Efficiency is tied so closely with the heat extraction of any given system that it's hard to compare when all RMH's are site built and use different extraction and thus will have different efficiencies even with the same combustion unit. At any rate, if you watch my video here: Rocket Mass Heater tested with Flue Gas Analyzer you'll see how my cast core runs, and of particular note is the extremely low CO numbers. When running full out it is typically running at less than 10ppm CO. I've never tested a brick built rocket mass heater that was able to run at that low level. Not to say they aren't out there, I just haven't run into one. At any rate, yes, I believe a highly insulated core performs better than a core of the same design built using bricks. That's my opinion, I'm sure you'll find differing ones out there. Thanks for the comment.
Thanks for the video! I've watched it many times but ironically didnt sink in that I'm trying to help my dad build a 6" and not 8". Would you still use the same dimensions as you have here? How many bags of perlite and fire clay did it end up taking? Thank you.
Brian, to make a 6" use the same overall Length and Height for riser/feed stubs, but make the passageways 5 3/8" sq. instead of the 7 1/4" shown here. This one took 3 bags of Lincoln 60 clay and 4 cu/ft perlite. Good luck on your build.
My biggest concern is equal cross sectional area past the core and heat riser. My core and riser will be 8 by 8 throughout. But how does that apply to my barrel. Center it and shoot for 4 inches on each side of the riser? Also how does that apply to how close the riser top is to the barrel. Iv herd 1 inch works well? Also the manifold that connects the bottom of barrel to 8 inch pipe...so does the manifold need to be as close to 8 by 8 as possible to acheive equal cross sectional area as well?? Or would something like a 12 by 6 register box that transitions from rectangle to 8 inch round pipe work just fine. I'm shooting for equal 8 by 8 throughout jus wonder how to apply that to inside my barrel and manifold at bottom of barrel going to round 8 inch pipe. Can't seem to find specific info on this. I'm going for the best rocket effect possible. Thanks a million buddy let me know when u get a free min....
Bigger is always better once you are past the riser, but you can't have any restriction, so barrel top gap should be LARGE, 3"4" minimum, larger is fine. Side gap, as big as you can make it and still insulate the riser, say 3" minimum or so. Manifold is important to be oversized, and you have to think of the passage in 3D. The box may work, even bigger would be better. When you get to that area do everything you can to "port and polish" that thing, just think flow. That's how you get it to rocket, no restriction, all flow.
Thanks for the quick reply. That's good to know as I'm also in the Pacific Northwest. I don't much care for the aesthetics of exposed cob...for the mass I'm planning to make a cement fiberboard box, tile it on exterior, and put piping & cob on inside. I'm also looking at ways to get rid of the ubiquitous & unsightly 55 gal drum for the heat riser cover. :) We don't have clay here in our soil, what kind of clay should I be looking to buy? Do you add straw to your cob? Thanks!
Hey, nice vid ! Great to see a stove made of refractory materials. When you cast this, did you really ram it? Also I'd like to know after 24 hours would you have been confident to invert it and remove the wooden base for another 24 hour aircure? Im not being critical, just wondered if a longer air cure and a milder heat cycle would have prevented a lot of the cracking due to thermal stress. I plan to reproduce what you did here, but I may use some firebrick grog in the mix. Thx again!
Broaudio, what size hardibacker do you need? I'm going to build one this spring and stock up on fire cement, they are clearing it out around here! Thanks
I burned mine for 3 full seasons and it held up fine in the burn areas. The mix is soft, so it wears from wood feed abuse, but a handful of mix every month or so is all it takes to patch it up. I would say it's comparable to soft brick. I don't recommend firebrick, they make a very hot feed that creates a whole host of problems. You asked about fiberglass, and I don't have an amount for you. You want it evenly spread as single hairs throughout, but no clumping. Not much, a few handfuls will do it. Good luck on your build.
Great project! I would like to know if perlite or vermiculite is safe to use since I understand that they expand with heat. Did you ever have any crumbling or cracking of your stove? Thank you for sharing!
Is this the cast you used for your home mass heater? You mentioned that you'd hope folks would look into casting their firebox. I've been thinking about casting, so I' m curious as to what you meant! Thanks Goethe great videos!
I'm currently building this and am wondering how you mix the clay, perlite and cement. I'm using the tarp method and found it to be a lot of work. There must be a better way?
Are there alternatives to fiberglass for adding reinforcement? I have a terrible aversion to fiberglass ever since I got into some of the pink stuff as a child.
Absolutely Marc, you can even omit it entirely. My home system has this mix with no fiber and it's holding up just fine. Alternatives would be stainless steel fiber/needles, wool, fine jute, etc. Most will burn away on the inner surfaces, but as you get to the outer skin quite a bit should hold up. Frankly, I'd suggest omitting it and capturing the whole core with a good, strong cob mix. It won't be able to go anywhere. Good luck on your build.
***** Thank you so much for responding! I have found your videos to be very informative and helpful. I am still a ways off from building my own but all of the information you have on your channel has been great. I own and often read through the Rocket Mass Heater book by Ianto Evans but that book does not really go into cast cores and from the information you have it seems they can be better in many ways vs firebrick.
the other option is using poly propyelene fibers (cut up from the plastic rope). they will burn away, giving micro gas outlets for the water in the mix, and reduce cracking. others use some sawdust. not to hold it together like fiberglass, but again to create steam outlet. can also use S glass, the white fiber glass in the pink plastic wrapper. old style pink glass is hard glass. the S glass is less brittle for some reason, less picky, less reactive to skin. I don't know why. but always use a respirator and cover yourself well when working with glass. i've worked with both, and the white glass does seem to be easier on you.
Another couple questions: what would happen if the walls were only 1" rather than 2" (using the store-bought insulating refractory). Also, the instructions on the store-bought insulating refractory advise against making molds out of wood because as the wood burns off, spalling will occur on the surface of the refractory cement, significantly decreasing its insulative efficacy. How to prevent this?
Just finished! And to be honest after I was done, I said never again lol. Digging clay and mixing it by hand was not fun. Then I fired it up, and I love it. Couldn't have done it with out you're help, thanks!
Thank you so much for sharing all your expertise! I just watched your sourcing video, as well as many others! I am in Mexico, sourcing is a big deal as the cheapest thing is always reused here ( which, basically, is a good thing…just making it harder to find!!!) . I love the idea of the cast, I didn’t find a plan or instructions so I am not sure yet to what will get into my own soon . Bricks are definitely very cheap here, though fire bricks will be a killer. 😅
Things to consider: shipping for me: no company can ship directly to my place (no address, only a gps location and the looong Camino makes it impossible), so I will have everything that will be shipped, to a friend in the closest city. I am a woman, I had a brain injury so I don’t have your strength anymore guys 😉. The maximum I have been able to carry and install are solar panels. For that reason I am planning with the smallest pieces I can.
My questions (or do you have videos answering all these questions ). I will keep going and watch
1/do you have specific videos on plans for the core?
2/What matériel goes in?
3/Can we buy doors by itself?
I plan to build it in a wood cabin (working on the plans now: I will build a maconery part to support the weight on that part, my understanding is that it is safe with the fire, am I correct? )
PS , I am in the mountain just up to a subtropical climat. Sounds weird to build a mass stove in subtropical climat…I know…though mountains are coooold in winter and still extremely humid. Without heating I have mold ( and mold+ neurological issues= big no no)…
just found your site. I have been promoting survivalist techniques to family and friends to show them you can live off the grid.
Lol I was trying to read the dimensions off my phone, but i took out the laptop and its much better, also appreciate the effort put into having the exact measurements scrolling along the bottom, thanks!
Wow. These RM projects of yours just keep getting more and more interesting. Your editing is looking good too. Nice work.
I just subscribed today. I really appreciate the rocket stove videos. They are wonderful teaching devices and I feel a lot more confident about attempting building one. Thanks so much for sharing this information. You are an excellent teacher. Loved the huglekulture video as well.
Thanks for the heads up, totally see what u mean. I was already thinking that several tiny cracks could prevent one huge crack. Just all part of settlement and transition from hot to cold. Right on man thanks!!!!!
Thanks for the quick comeback, I'll be picking up a wheelbarrow tomorrow
Right on. I think I get it!!! Bigger is better because the corners cause drag....thus reducing the area of free flow.. Whether it be at the riser top,barrel sides or bottom manifold....thanks alot bro
absolutely BRILLIANT! Just what I have been looking for! Thanks Bro :)
I do thank you for your patience with me in my misunderstanding. NOW you are perfectly clear... Again, for my part in not understanding... Please forgive... I just want to make sure that I proceed and don create a problem... so AGAIN... Thank you for your patients and willingness to explain...
Respectfully, bob
P,S, YOU HAVE DONE A GREAT JOB IN YOUR PART OF EXPLAINING YOURSELF AND THE PRINCIPALS...
Great ideas! Beautifully done. Thanks for sharing the details.
You're doing what I've been dreaming about, fantastic stuff. Thanks.
Thanks again for this inspiring video! I made the mold box yesterday (out of wood, not hardibacker.) Today I did some research into the materials. (continued in next comment)
This is brilliant. Love what your doing with the technology. In some sense, these cast models could be used as the basis for a small scale production business. Thanks for documenting and sharing!
Sounds great man, I will defiantly go 2 in thick on burn chamber. luckily iv got refractory to burn!!! Pardon the pun. Thanks a million bro I feel tons better about it now. This is my first build and it's in my shop. But I'm taking it slow trying to research and absorbe all info possible. Thanks again for your time and advice. I'll let u know how she turns out!!!
Curtis Webb Cool man, so glad to help. One thing I should mention, and it's not a problem at all but you should mentally prepare for it since it trips many people up. The reason to surround the whole thing with the clay/perlite inside the brick surround(in addition to being crucial insulation) is to isolate the whole thing from moving, so it doesn't make a damn bit of difference if (when) it develops cracks. In other words, it's probably going to crack at some point. It doesn't matter, at all. Do not freak out! That's what all the stuff around it is for, and why it's referred to as a "core" rather than a stove. The temperature changes so greatly and rapidly so often, and differently in different parts of the core, that it's just going to happen at some point. Just thought I'd let you know, so many people can only see a crack and think "fail", but if you accept it as part of the build it will have absolutely no effect on performance or longevity. Just thought I'd let you know! Good luck man.
Great job with this design; I like the idea of precast to using bricks, also great job with providing the information of your build. I am dissatisfied with my “J” tube build, but was looking for a light weight-portable unit with a bit different use. I also have looked at using fiberglass matt as an outer skin to the Kaowool insulation dripped in ceramic slurry the test did quite well. I believe I will look into the next tube build alone these lines as you have shown. Thanks for posting.
Nice work!
I like your ideas and solutions.
Understanding the requirements and risks, plan with some margin for error, and test the stuff before you install it. Good practice!
great build. and great information. thanks !
milled glass fibers are available ,used in FRP mold making would help homogonize the mixture.
you are quite capable at taking a basic design and streamlining production and adapting it for more versatile applications. well done and continued success.thanks for demystifying the inner workings.
Thanks , the way I was thinking was to put the feed outside and go threw the wall with a J tube and that way the barrel will be inside that way I will get the heat off of that also .
Well, I made my casting yesterday. Using the amounts of fireclay, fire cement pearlite and fiberglass that you recommended only filled the form up to the top of the burn tube. I had to slip clay bricks in the sides for filler and mix up a bag of quickrete and vermiculite to top it off. I hope the thing holds together. I think I should let it air dry a bit longer before firing it up. I used concrete/verm. for the chimney also.
It is doable, i think.
It will crack a lot most probably but we dont mind that until it holds together. So i recommend to put some reinforcements inside. Like reinforced concrete, but with long glass stripes.
Painters have tape like (thin veil or tissue like) material for dry wall joints. We could use that to keep the piece from cracking, (or at least not to fall apart) by placing the stripes near the surfaces of the piece.
Unless your house is so tight you can take it into space, I wouldn't have thought it was a problem, the negative pressure will find any leaks, there are always some, even in the best built homes and it's not just doors and windows but roof and walls as well, although your walls will probably be pretty good but you get the idea.
Thanks for the info, I like the cast J tube a lot better then fire bricks.Thinking about some bolts imbedded in the area where the riser goes to anchor the riser to the J tube, when the rise is also cast like you commented about.
So we were on a ski trip over weekend and we lite a fire in fireplace and that darn fire didn't last long I woke up saw it was out tried lighting it again but nothing . Wish there was a rocketstove there lol . I gotta get motivated one of these days and make a core lol
Thanks very interested in a similar project.You do very informative videos!
broaudio just so you know rounding the top of your feed chamber is a no no if you are burning larger sized wood. that clean sharp edge helps brake the fire from climbing upward on your fuel. like your mix. I gotin away from using fire clay.. Iam using small amount of Portland & feed clay (from feed store),perlite & mix thick then add cat liter(low moister at this point). This insulation mix is so good I ran the exhaust under my burn chamber & bench so I can load while sitting on it .
Excellent video bro!
Suggestions for the cheap asses like me: Use fire clay and silica sand for the insulation mix. 2 parts sand to 1 part clay, mix like the video shows. Very cheap. This is used in to make small charcoal foundries for melting aluminum and holds up well. MUCH cheaper than premix refractory cement. Makes a good crack patch compound too.
You can also add some small wires (chicken wire, coat hangers, etc) for "rebar" to add strength and help prevent cracking.
Great video and informative too! The following video doesn't seem to be a continuation.of the above video.
Good job, thanks for sharing
Thanks for the instructions and the measurements ;o)
srry, I didnt catch that, how much ripped up riberglass insulation did you use?
muito bom, gostei da sua idéia.
Nice job
Thank you.
Fire cement & Fire Clay? Can you give us more information on these? Are they commercially available products or ingrediants?
Broaudio,
Really nice and simple explanation...thank you.
Just a couple of questions:
>is the finished inside dimension of the core (using 1/2" OSB) to be 6" square for a 6" system AFTER the wood burns out or 5 3/8" square (as you indicate to Mark)
AFTER the wood burns out?
>Also, in your other videos you show one of your stoves with a viewing window/air supply, how long should that tunnel be before the burn tube begins?
I think I'm finally settled in now and HOPEFULLY start my build of the cast core RMH. I have two questions: (1) I always thought that concrete (including refractory motor) needed TIME (the more time the better) to cure VERY HARD (which is what I want. Yet, with your build, according to you, "I lite a fire the next day and let it rip"... My question is: "will my cast core build be harder and stronger if I were to let the pour set up (Without heat) for a couple of weeks before actually liting it up for the first time. My second question is about 'the proportions' of clay/perlite (1:1; and/or 14 parts of each PLUS whatever amount of refractory mortor, I can afford. My question is: "Approximately how many 50 lb bags of clay did you end up using to build both the stove AND the riser? ( I'm guessing, what, about 150 LBS of clay and equal amounts of perlite (via the suggested ratios????? I appreciate that your very busy but I would really like some idea before I proceed (Hopefully this week (before the cold sets in)
+Bob johnson Bob, if you want a hard cast core, you don't want to use this mix. This one makes a soft, insulated "liner" for a cob surround. I can tell by your question that you won't be satisfied with it, and it will crack. I recommend finding a commercial castable refractory if what you want is concrete-like performance.
If you do go this route, your estimate is about right, 150 lbs of clay and an equal volume of Perlite. Good luck on your build!
Very cool. Now I need try one of these too. Haha
I hope you will be doing riser video very soon.. Good job and thanks in advance
Do you know the size of the room in which your friend is going to heat with this stove? How well does it do?
Preaty cool idea on the rifleing designs using a rope in the casting BUT broaudio is right it will just create drag I'm afraid. Iv been studying the laminar flow effect, yall should check it if your unfamiliar with it. It's fluid dynamics, basically it sez the layer of air closest to the rough brick surface inside the system allmost stalls, causing the layers of air above it to tumble or mix!!! Lots of fluid dynamics going on inside these things.....
Was wondering about the "MASS" you used for your Rocket Mass Heater? Which materials are best. Was thinking of using rocks and stones found on site (on my property that I would dig up... (2-10 inchs in size. Would that work? I just have a limited amount of 'COB" (clay) hence wanted to use larger ROCKS (10 inches ini size) for the mass. I would use the COB to act like motor to hold it all together. Your thoughts please.
Bob, that's a great way to go. Rocks are better mass, but are tough to couple effectively. If you seat them all in cob and make sure there are no air gaps, you'll have the best of both worlds. Monolithic and relatively high mass. Good luck on your build, thanks for the comment.
I have played with cob alittle last summer now, and had a blast, was hoping to make an all natural version, would the sand / clay / straw mix not hold up in a RMH outdoor kitchen application?
Did you see any damage to the wood around the core from burning it? I wanted to put one of these in my home.it would rest on wood floor I am trying to figur out if the core or any part can get hot enough to cause my floor to catch fire.
That was kind of my question. I am guessing to put it in a raised foundation home I will need a thicker bottom then. Maybe an air gap.
Very nice btw..!
FInnaly getting to it.
If the burn square ection (7.25x7.25) is smaller, would I need to shorten the horizontal 9 1/2" burn chamber?
No, keep it the same length. Any shorter and it becomes difficult to fit the barrel, you need a little distance from the wood feed. Hope that helps.
Hi Matt! have just finished my own outdoor half barrel firebox with 20 ft heated bench in a c shape. having my first party around it this Friday evening. Thanks for the tips and inspiration. Pics to follow. I want to cast an 8 inch batch box with a window on one side. Do you have any suggestions?
Great build! Love the stuff you are doing with rocket stoves and your designs have given me some inspiration on what I can do when I start building in the spring. Two questions: As to adding the fiberglass, would polypropylene fibers (fibermesh) work? Would even less water in the mix be possible and keep it from cracking as much? Thanks for taking the time to make and post the vids!
was looking into making my first rocket stove i am going to be using it to heat a h homemade hot tub outside wich will make for a good trial situation and i love your idea i was wondering what u would think about my idea of making the internal core out of firebrick and casting the same mixture you are using aroundthe brick i am thinking this will add a tremendous amount of insualtion value. I live in maine the ground is almost thawed enough to start construction and will be posting a video soon
Hi,I am investigating a iron rocket stove insulated with 2m3 of sand.
I like to create a sandbattery with this. Anybody any idea if the iron will melt or will be deformed.?
Insulation is not preferred because I like the sand to become hot.
Any suggestions are highly appreciated.
Hmm that makes sense with the air gap, but is that layer if perlite before the durock below the brick tunnel supposed to be structural? Like one would just make a level layer if clayperlite and put on durock and build the burn tunnel? Thanks!
Great work, thanks so much for sharing. Looking forward to the riser construction video.
Have you experimented with the shape of the poured burn chamber to make it more rounded on the internal square corners? Do you think this would make any difference?
peace
~//~
Can I use castable refactory cement? It is a dry mix, not the premix.
Also you said in the video to use as much as you can afford, so would it be stronger to put two buckets of the castable cement to one bag of clay, or would that just be a waste of money?
Maybe as a good idea for nex projects:
Use with some safety precautions water (yes water) as the mass. There is no comparable good substance to store heat such as water . (you can do your own research -> heat capacity per kilo)
For comparison>
1 (!) Kilo of water stores more heat (at 99°C) and at the same temperature than:
- 4.5 kg aluminum
- 9 kg iron
- 11(!) kg of copper
or
- 5,8 kg asphalt
- 5 kg Solid brick
- 4,2 kg calcareous sandstone 1
- 4,7 kg concrete
Even if you bring 1 kilo of aluminum to 350-400 ° C,
1 liter / kilo of water (with 99°C) still stores more heatenergy than the kilo of aluminum. (purely to the understanding)
And water is a lot cheaper than the mentioned materials^^
If you take a thermostat from the automotive sector (92-95 ° C) and a large IBC container, you have the cheapest and most efficient heat storage. Which can not overcook so quickly (1000 liters of water need "some" time)
Should it come that far, we have the thermostat that can push away from the heat source ;)
Very inspiring. I would like to hear about the benefits of a cast core vs. built up from firebricks. Where can I read up on that?
I have and idea that would help to create a vortex within the flue. Wrap hemp rope helically around a 6 inch PVC pipe inside form like rifling inside a gun. Cast the refractory material around the hemp rope. When the cast of refractory has solidified for a day, withdraw the PVC pipe, leaving the rope in place. On the first burn the hemp rope will be consumed, leaving a nice helical twist within the inside diameter of the stack. What do you think?
Curtis Turner Hi Curtis, no need, it will only add drag where you really don't want any. Don't over think it, the J design is deceptively simple yet achieves complete combustion very effectively. You really can't make the burn much better. You'll get better results focusing on good insulation and sealing of the core, and good flow through the whole system. Good luck on your build!
Thanks for reply. Learning a lot. So if you want a front window like you have in your home, should you plan for it in the core stage, or just cut it out later?
Is it possible to add clean out hole to this mold?
need to make a water heat. can you replace the mould with insulating ceramic fibre board and no need to mould using fire cement mixture. need a super hot flame coming out of the riser, to heat a 44 gallon water tank held above.thanks
Looking at the video, you used fiberglass matt for insulation, right? How much did you need? In the video you jumped from the fiberglass matt all shreaded up, to the photo of mixing the pearlite and fire clay. The fiberglass is not used there, right?
I'm wondering about the fiberglass myself. Is this just any normal fiberglass, or does it have to be specific for refactory?
Hey, sorry I missed this. RUclips is sorta awkward for communicating well, I do try to reply as quickly as I can. I used a couple square feet probably, all shredded. And yes, I mixed it into the perlite and fireclay. It's not necessary, but gives a little better tensile strength to the mix.
Brian Beck
Brian, it's just regular fiberglass. It most likely burns/melts away in the inner layers, but should give some strength to the outer. It also allows linear clay structures to form along the length of the fiber, increasing tensile strength. You can google fiberglass in ceramics and find out more about how it's used there. It's similar here.
Would of love to have just of seen you mix your mix along with the actual info.
I must not have been clear. do I leave the fiberglass into the bottom of the 16 X 16 X 32 box as well as on top box OR do I shread the fiberglass into 'wispie bitt' (without additional fiberglass batts on the bottom and top ? (i.e.) I THINK you're saying "Shread up a bunch of fiberglass (don't leave it in batts????
I am actually building a rocket mass heater for my hoophouse right now. I am getting a lot of smoke back out the feed tube. I like this design. I have a question regarding the riser tube. If I am using 8" tube, should I just use 2 - 8 inch tubes screwed together to make a 16" tube and insulate between the inner and outer? I considered using your steel half barrel design, but there will be a lot of water in the hoophouse and thought it would rust out. Thank you for your videos. Much apprec
Thanks for the reply! I gave that book a couple reads, and I did notice a section on building on wooden floors. I just really understand it. Have you done an install on a regular floored home? I am putting mine in a insulated shipping container and I can't wrap my head around what to put underneath the combustion chamber. Right now the floor is Aluminum T channels, then 5/8 plywood on top. I am going to use Roxul, but I need a subfloor, but then won't the wood just catch on fire?
Dude, you're the best- I've been looking for something like this and I was getting a headache, tryin to figure out measurements and proportions (and motivations) out of all the piecemeal info out there, about RMHs! And it seems everyone is using fire brick but it's not much of an insulator. Your way, I can pour a hybrid aircrete mixture (cellular concrete with basalt/ fiberglass and/ or vermiculite) and have a core that's superior in insulation and very LIGHT. And with aircrete, I can cut out my cleanouts easily with a wood saw. Instead of flue vent distribution, I'm going with bell courses. Thank you! Any insight you have regarding my plans would, of course be much appreciated.
You are welcome, thanks for the kind words. I think you have a good handle on things. Portland based cements won't handle the temps in the core combustion areas for long, but you could probably run it for a while before it deteriorated too much. If you want it to be a forever build, I wouldn't recommend it, but as a first build or a step in a progression, I think it's probably great. Hope that helps.
Yes; then perhaps I should try aerating fire clay and my fiber additive (with or w/o fireplace mortar) for the pour into the core mold... do you think I'll have to burn-cure this afterwards? My preference is to cast a light core that I can easily lift but that will not need repair or replacement down the road. I suppose it's time to run some experiments and for what it's worth, I'll let you know what I discover. Thanks so much for sharing your ideas and perspective.
Getting closer to casting - wondering if one were to scale this down, say to a 4" outlet, would it be to much to assume that I could just cut my dimensions for the pieces in half??? The shop is only about 400 sq ft. Thanks
Richard, you may be able to, but 4" systems tend to be very tricky to get right, and are a pain in the butt to feed in my experience. I'd recommend no smaller than 6", you can feed less wood if you don't need the full output. For a 6" system make the square passageways 5 3/8" square or so, and leave the overall lengths and height of all outside dimensions the same. A big pitfall of scaling down is you can leave yourself with no room for the riser/barrel combo if you shorten the overall length by too much. Good luck on the build, and thanks for the comment.
Do you have any idea approx. how much fiberglass insulation you used (in your mix? I am confused because first you show your marking the box with 4 inch of fiberglass and then shreaded or tore up the fiberglass for the mix. DO I DO BOTH.(leave a 4' mat all around). or just enough fiberglass (eventually torn up) and mixed in with the clay. perlite and fire cement?
Nice clean build, so is this meant for indoors? What keeps the heat from burning the floors?
Can you make the burn tunnel longer? The riser and burn tunnel have 2 to 1 ratio!
Add Refractory Reinforcing 1" 430 Stainless Steel Needles and you won't have cracking issues (like mini rebar mixins).
Thanks once more. Is there a recipe for this piaster? And is this the same formula used to plaster stucco?
Nice job ! How are you ? I would like to know if you ever had any ideas for heating water for a radiant heat ? I have a sand blast shop ,it 18 by 40 and I installed the tubing in the cement floor . I can not have a flame inside because of the big fan to suck out the dust , so it's hard to heat . But early just want to take the chill out ! Any ideas , I have built a Gasifier so I'm a little familiar with this but always looking for good ideas . Thanks and like all your videos .
At the end you say, "then you're ready to fire 'er up". But presumably you would need to connect it to an exhaust pipe before burning, correct? Or are you moving this whole core and burn chamber into place in the house AFTER you finish constructing the core components?
The latter. I build them outdoors, or, rather, in my wide open shop, and then burn it dry before moving inside. You could cast in place, and connect the exhaust first, then dry it out in place. I actually think this is a better way to go, but in the case of the video I was building it for a friend, so was working remotely from the final install site. Hope that helps.
***** How many burn hours does it typically take before the core is ready to set in cob? What signs are you looking for to know that it's fully cured?
I don't think I could put a time on it, but the idea is to get it firm enough that you can move it without it sagging or deforming. I would say that a few(4?) hours of burning will certainly not dry it entirely, but should set the mix so you can move it safely. Once in place you can start cobbing around it even if it is not fully cured. Thanks for the comment.
the sheet 1/4" HardiBacker cement board is burned?
How is the cast core holding up? This looks like the best way to build a stable reaction chamber provided the materials are working well. I was contemplating pouring a ceramic core because of it's resistance to heat, but I don't know if that is possible or if it would work..
Hello broaudio. Much respect. I like your cast core instructions better than most I have seen on RUclips. My question is I have a high quality industrial dry refractory mix. Rather large amount came my way by luck. I read in the comments that this type of refractory is not a good substitute for the gallon size ready mix stuff that contains sodium silicate . so my question is would I b better off casting my burn tunnel out of pure refractory cement say 1 in thick, then fill the bottom of my 16 by 16 by 32 inch outer form with fireclay perlite mixture,allow it to cure, cast my burn tunnel ,set it on the 4 inch thick perlite fireclay bottom, then complete the rest of the infill around the burn tunnel with perlite fireclay. Basicly a 1 inch thick burn tunnel or square u shape...surrounded on all sides by insulating perlite fire clay mix. By the way I constructed a 16 by16 by 32 inner dimensions box out of firebrick for a perminant ridged form, instead of using cob to surround the core. Also plan to line the brick form box with heavy duty foil shiny side up to help reflect heat back inwards and to keep the core mix from sticking to my brick. As shrinkage occurs I plan to fill the surrounding crack between firebrick box and core with sand, for support and shock or tremer resistant cushion for the core. Iv done a ton of research on RMHs and homemade and industrial refractory and feel that I have only scratched the surface. Please let me know if I'm on the right track with this idea... Thank u so much for your time and your awesome videos.
Hey, thanks for the kind words. Your plan is excellent, and is really the better way to go. My mix here is just a DIY mix for folks who can't source true castable refractory. If you have enough refractory you might up the wall thickness to around 1.5-2" just to add a bit more resistance to wood knocking around in the feed, but overall I think you will come out with an awesome stove if you build it exactly as you describe. I've done the brick surround and it's an excellent technique. Good luck!
Build a 5 Floor Rocket-Mass Heater slit ranch house 5 half Floors gas heat now !
HAve you made any new heaters this year?? Tony
great!
Very informative! I'm thinking about putting one of these into a building that I'm (again planning) on making a "tiny home/cabin" and I found your video very useful. I'm going to sub you and hope to continue to learn from you over time. Quick question, do you know of a well rounded resource that I can use to learn the basics in RMS design by chance? Thanks in advance!
I'm confused. Forgive the noobish question. With a riser, could you still add an exhaust that goes runs under a bench? Are you going to add an entrance to clean out ash?
Dyer, did you mean without a riser? I'm confused too! This is part one, see my other videos for part two which is casting the riser. This stove will have a riser, and yes it can power a bench run. No ash cleanout in the core, it's a bad idea in my opinion. It's easy enough to clean out what little ash there is with a small scoop every week or so. Clean outs are very important in the flue runs under the bench, that's where most of the fly ash accumulates. Thanks for the comment.
A quick question:... I am thinking of buying 'chimney clay flue pipe' (8 inch) for the burn chamber and riser rather then the hardy board build. I would 'insulate per your recommendations to produce an insulated box. My question is will the clay flue pipe build negatively effect the efficiency, etc.
have you considered using chicken coop wire or similair for a rebar effect? maybe it would help minimize the cracking? that's what I would experiment with. thanks
What is the source of your research on the efficiency of the cast core vs built with firebricks? If a cast core is more efficient, then it must be due to the insulating characteristics of the cast material, correct?
Hi Douglas, in this video I was hoping to convey that I felt that the insulated core offers better performance, not necessarily efficiency. Efficiency is tied so closely with the heat extraction of any given system that it's hard to compare when all RMH's are site built and use different extraction and thus will have different efficiencies even with the same combustion unit. At any rate, if you watch my video here: Rocket Mass Heater tested with Flue Gas Analyzer you'll see how my cast core runs, and of particular note is the extremely low CO numbers. When running full out it is typically running at less than 10ppm CO. I've never tested a brick built rocket mass heater that was able to run at that low level. Not to say they aren't out there, I just haven't run into one. At any rate, yes, I believe a highly insulated core performs better than a core of the same design built using bricks. That's my opinion, I'm sure you'll find differing ones out there. Thanks for the comment.
thanks for your reply. I've looked for the HVAC tape and it's only rated to 200 degrees Fahrenheit. Is that within reason for a RMH?
how did u use the fiberglass?
Thanks for the video! I've watched it many times but ironically didnt sink in that I'm trying to help my dad build a 6" and not 8". Would you still use the same dimensions as you have here? How many bags of perlite and fire clay did it end up taking? Thank you.
Brian, to make a 6" use the same overall Length and Height for riser/feed stubs, but make the passageways 5 3/8" sq. instead of the 7 1/4" shown here. This one took 3 bags of Lincoln 60 clay and 4 cu/ft perlite. Good luck on your build.
My biggest concern is equal cross sectional area past the core and heat riser. My core and riser will be 8 by 8 throughout. But how does that apply to my barrel. Center it and shoot for 4 inches on each side of the riser? Also how does that apply to how close the riser top is to the barrel. Iv herd 1 inch works well? Also the manifold that connects the bottom of barrel to 8 inch pipe...so does the manifold need to be as close to 8 by 8 as possible to acheive equal cross sectional area as well?? Or would something like a 12 by 6 register box that transitions from rectangle to 8 inch round pipe work just fine. I'm shooting for equal 8 by 8 throughout jus wonder how to apply that to inside my barrel and manifold at bottom of barrel going to round 8 inch pipe. Can't seem to find specific info on this. I'm going for the best rocket effect possible. Thanks a million buddy let me know when u get a free min....
Bigger is always better once you are past the riser, but you can't have any restriction, so barrel top gap should be LARGE, 3"4" minimum, larger is fine. Side gap, as big as you can make it and still insulate the riser, say 3" minimum or so. Manifold is important to be oversized, and you have to think of the passage in 3D. The box may work, even bigger would be better. When you get to that area do everything you can to "port and polish" that thing, just think flow. That's how you get it to rocket, no restriction, all flow.
Thanks for the quick reply. That's good to know as I'm also in the Pacific Northwest.
I don't much care for the aesthetics of exposed cob...for the mass I'm planning to make a cement fiberboard box, tile it on exterior, and put piping & cob on inside.
I'm also looking at ways to get rid of the ubiquitous & unsightly 55 gal drum for the heat riser cover. :)
We don't have clay here in our soil, what kind of clay should I be looking to buy? Do you add straw to your cob? Thanks!
Hey, nice vid ! Great to see a stove made of refractory materials. When you cast this, did you really ram it? Also I'd like to know after 24 hours would you have been confident to invert it and remove the wooden base for another 24 hour aircure? Im not being critical, just wondered if a longer air cure and a milder heat cycle would have prevented a lot of the cracking due to thermal stress. I plan to reproduce what you did here, but I may use some firebrick grog in the mix. Thx again!
Broaudio, what size hardibacker do you need? I'm going to build one this spring and stock up on fire cement, they are clearing it out around here! Thanks
Great project, thanks for sharing. How will this cast core stand up over time compared to firebrick or regular soft brick, or is it too soon to tell?
I burned mine for 3 full seasons and it held up fine in the burn areas. The mix is soft, so it wears from wood feed abuse, but a handful of mix every month or so is all it takes to patch it up. I would say it's comparable to soft brick. I don't recommend firebrick, they make a very hot feed that creates a whole host of problems. You asked about fiberglass, and I don't have an amount for you. You want it evenly spread as single hairs throughout, but no clumping. Not much, a few handfuls will do it. Good luck on your build.
Would it help to coat high wear areas with Water Glass ?
Is the mat fiberglass that you tear apart put in the bottom of the form or mixed with the clay?? Thanks
It's mixed in with the rest of the ingredients to help bind it together. Good luck on your build.
Great project! I would like to know if perlite or vermiculite is safe to use since I understand that they expand with heat. Did you ever have any crumbling or cracking of your stove? Thank you for sharing!
Is this the cast you used for your home mass heater? You mentioned that you'd hope folks would look into casting their firebox. I've been thinking about casting, so I' m curious as to what you meant! Thanks Goethe great videos!
I'm currently building this and am wondering how you mix the clay, perlite and cement. I'm using the tarp method and found it to be a lot of work. There must be a better way?
Are there alternatives to fiberglass for adding reinforcement? I have a terrible aversion to fiberglass ever since I got into some of the pink stuff as a child.
Absolutely Marc, you can even omit it entirely. My home system has this mix with no fiber and it's holding up just fine. Alternatives would be stainless steel fiber/needles, wool, fine jute, etc. Most will burn away on the inner surfaces, but as you get to the outer skin quite a bit should hold up. Frankly, I'd suggest omitting it and capturing the whole core with a good, strong cob mix. It won't be able to go anywhere. Good luck on your build.
***** Thank you so much for responding! I have found your videos to be very informative and helpful. I am still a ways off from building my own but all of the information you have on your channel has been great. I own and often read through the Rocket Mass Heater book by Ianto Evans but that book does not really go into cast cores and from the information you have it seems they can be better in many ways vs firebrick.
the other option is using poly propyelene fibers (cut up from the plastic rope). they will burn away, giving micro gas outlets for the water in the mix, and reduce cracking. others use some sawdust. not to hold it together like fiberglass, but again to create steam outlet.
can also use S glass, the white fiber glass in the pink plastic wrapper. old style pink glass is hard glass. the S glass is less brittle for some reason, less picky, less reactive to skin. I don't know why. but always use a respirator and cover yourself well when working with glass. i've worked with both, and the white glass does seem to be easier on you.
Another couple questions: what would happen if the walls were only 1" rather than 2" (using the store-bought insulating refractory). Also, the instructions on the store-bought insulating refractory advise against making molds out of wood because as the wood burns off, spalling will occur on the surface of the refractory cement, significantly decreasing its insulative efficacy. How to prevent this?