Rocket Mass Heater - Autopsy 

Its great to have someone like your self that is willing to show his miss haps. It just show that you have integrity and shit happens. With out experimentation how would things ever improve. Keep up the great work. Greg

I'm always impressed with your dedication to this project. So so so sooo much RND in this green house and I'm so thankful you share all of your triumphs and mishaps with us. I can't wait to see your next design!

Great breakdown. Amazing how much I learn from other people's failures! Sometimes more than from their successes. Scientific process is fun. Thanks for posting this! Too many people only post the stuff that worked. Note to self: avoid rock wool and cement when building rocket stove.

I'm a refractory bricklayer...I would not recommend concrete anywhere within your unit as it explodes at about 600 degrees C. Which is easy to achieve in a rocket stove. Definitely build it with fire brick...and the cheapest ones are the ones you want...about 50% silica 50% alumina...they'll handle the thermal shock a lot better. Also make sure you where a respirator when cleaning the stove or working with rockwool...ESPECIALLY after it has seen heat...it becomes worse than asbestos

And I neglected to say how very valuable this information is. Extra special kudos and a hug for posting it!

black smoke I got was from the rockwool. When I did the autopsy on mine most of the steel flew was gone or rotted. I've now replaced the firebox with firebrick insulated with rockwool, sand, and the rubble from the first attempt. Clay is hard to come by this time of year so instead I'm useing a morter mixed with perilite and sawdust to insulate, seal and create a thermal mass. Thanks again for shareing, I've truly been inspired, I got a 12' 3v 5/8 dome half cut, before the rocket crash.

Really good to see an autopsy. Brilliant project & very well presented too. Thanks!

My bad... Please forgive me. I think your entire project is fascinating...

Wow, shows you just how much heat these things can generate! Great video and I look forward to more! Take care, Jeff.

Here's to the good, the bad, and the ugly. Thanks so much for sharing!

the problem with "benches" is that they radiate their heat out slowly. If the water stayed in the tank, this wouldn't be a problem, but it's getting pumped into the grow beds which have a huge surface area and radiates out the heat. This design works by heating both the water and the air at the same time, and any extra heat is stored under the building. Don't forget this isn't some cozy little cottage, it's a greenhouse that has very poor heat retention.

Thank you for sharing your failures along with your successes! So many other DIY channels never go back and revisit a project for evaluation. Again, Thank You!

That fire is hot hot hot. You are talented. I have trouble walking and chewing gum at the same time. You sir can play the piano and talk at the same time. Can't wait to see the new heat riser design.

Thank you so much for sharing this video so that we can all learn from your experiences. Keep up the good work. Love your videos.

fantastic vid! thanks for all your dedicated forensics!

major respect 8-) .. this is most important video I seen so far regarding rocket stove .. and there are plenty good and useful videos Thank you!

I am sorry your design was not perfect. You certainly deserved it to be. My very best wishes on the new design. Thank you so much for sharing this with us. From, just another fan of your work, fine videos and your character!

ok, I wasn't certain how much heat was going through there and thought it might have been a problem.Your whole project is great, I am just sorry to see you having set backs on it.

That laminar flow will get you everytime. Looks like another trip to the stainless steel yard. I saw a guy who uses quarter inch thick stainless steel tubing in his rocket stove. The place where I get my 55 gallon drums has a stainless steel drum but he wants $125 for it. They may be available in your area. But if you have a thick heat riser you may not have to worry about the drum. I am assuming you are using propane now. We need to hear the cost comparison. Keep up the good work Rob.

I've read a lot of peoples' clay pipes crack under the stress. I've replaced it with stainless and it's been working really well.

yup. So far the bricks are doing OK, but I do have some firebricks on order. We really don't have much clay in this area (and the ground is frozen) so it's just cheaper to go with the fire bricks.

My Friend it is still a good design. The amount of heat generated to cause that type of failure is increadable. That in itself was a success.

Yep. I think I was thinking of a similar situation to yours but concerning the barrel. I did learn from your video. Thanks. :)

when i first saw your video on the greenhouse i thought what is this idiot getting into ..by the time i finished watching all your videos i thought this guy is a genius ,,so i subscribed..great job..

thanks. I just finished rebuilding this today. I decided to make the heat riser 6" instead of 8" and slow the burn down a bit. I got a section of 304 stainless that I"m using as the riser. So far, the grates made from stainless are doing well so I'm willing to risk trying the riser with it. I"m planning on firing it tomorrow and test it out.

I haven't installed it yet....it just showed up today! I'm going to rebuild the entire thing using this and firebricks. I"m hoping to have it running again this weekend.

Wow im glad you documented this, I was going to use Rockwool for my heat riser, guess ill go with clay/perlite. Thanks for sharing!

Hi sir, I real love your videos, specially those about how you build things. I hope to see more about your rocket heater soon.

Hi web4deb, thanks for videos. I have being running a masonry stove for about 4 years now and one thing I have learned is that stainless near the flames will buckle, bend and corrode. Grates may be okay because they will get a cooling air flow and higher temps are probably reached when the secondary air meets the combustible gases. Have fun!

awesome cant wait to see your new design.

Awesome video!!! I have subscribed to your series and it is the only site on youtube I check regularly. I have a very small system using a window garden and aquaponics system do to living constraints. In the future I hope to incorporate your methods along with an earthship design. Your videos are awesome and if there is anything on the tech side I can do to help you produce more videos please let me know!

Experiencing single digit low temps tonite with 35 mph wind gusts. Spring maybe on the calendar, but winter is still in control! Extreme long burns here in WI and my wood bin is getting low. Its pallet time!

An interesting analysis. Your heat riser is experiencing some really intense heat. Just a thought; kiln shelf material (alumina) would tolerate those temperatures. They are fairly expensive, but depending on the life expectancy you would like for your heater they might be a solution. A pottery supply house would have information on alumina shelves. Stainless steel stove pipe might be a cheaper way to go but I suspect it wouldn't last more than a couple seasons.

I'll bet! At any rate, this is really awesome information. You should name your rocket and set up a memorial fund, donate button, for this rebuild - and the next, too, as I don't think you can afford the materials you'd need to prevent it happening again as I suspect something happened that is a bit more significant than merely "heat over time". If the black suits come to talk to you, let us know!

I have been following your excellent vids, lots of good information. I was wondering how long it would be before your RMH died. I built a 20' geodesic dome, last August, out of PVC here in Wisconsin. We know cold weather as well and let me tell you there is nothing more stressful than having to rebuild my RMH before night fall. I have had to rebuild 6 times! I learned many painful lessons. The riser really takes a beating. I exhausted most metal type risers and now use firebrick.

great video, i love it when others share their mistakes to prevent others from doing the same....i certainly have made enough mistakes already in similar ways, and will continue as i learn to reinvent meself thru life...mahalo

Ouch, sorry for the painful lesson. I noticed in your 1st vid that you didn't use 2 layers of fire brick for the combustion chamber. Absolutely love your dome and 'ponics set-up. How is the production during the winter months? Have you considered adding some HPS lighting for winter light augmentation? Signed, N. California Architect

yeah, I ordered a bunch...it should be here in a few days. Using concrete bricks is a big no-no, but it's all I had in a pinch.

There are a few suppliers in the States you could try that would be a fraction of the cost for all your refractory needs.....one ironically is called Bigelow Liptak, another is Harbison walker, NARCO, VRD, RHI, Vesuvius refractories. There's quite a few, but that'll get you there if you dabble more into refractory, or need repairs. Also consider castable refractory, as you can form and pour to any shape. It's the dry out that has to be followed correctly that becomes very important. Cheers.

Ok riddle me this batman: WHAT IF you made a 2' tall x 3' wide wall around the fish tank. Now before winter comes you fill that trench with compost. that way while the pile is composting it will generate heat keeping the tank warmed constantly without rapid jumps in temp. Relying on the rocket mass heater to heat the dome and the water is asking to much. P.S. I'm very jealous. Very cool stuff you did.

That exhaust travels 30' under ground, then up before it vents out...I don't think there's any sparks left in there by the time it vents. ;-) I was thinking about adding one more section to it anyway before the building official found it. ;-)

What material did you originally use for your inner heat riser pipe? If it was just black flue pipe or something else thin wall, simply upgrading to an equivalent diameter mild steel 1/8" wall or even 1/4" wall (if you can get it) pipe with vermiculite around it might solve the problem. My plan for mine is to use a 4" dia. mild steel pipe with 6" flue pipe around it, and vermiculite between the two, flowing through an old water tank and exhausting out the bottom of said tank via 4" HVAC ducting.

I'm new to all of this but am looking to do exactly what you did with a dome. I also get cold weather and have been thinking of heat. Would a cast iron wood stove with a water tank attachment for the aqua system to flow through work at all.

Thanks for letting us in on your troubles. How do you engineer reliability for 2500 degrees? I don't know... Many clays don't go that high...

As an inner liner, an old 100 lb propane tank will be around 1/8" thick, or more. Rockwool is no substitute for cementitious materials. Ash will not burn or melt.

Ok I get it. Very cool set up. i cant wait till you give the walk through video. By the way How many gallons is your fish tank and how many fish? also sq ft of grow area? and sq ft of floating raft? Thank for your past response. P.S. How cold is it out there now. I'm sitting outside wearing shorts and a tee shirt at 7:00 pm out here in Santa Monica CA.

I test burned for an hour with no problems. It's getting warm enough where I really don't need to do any long burns now! ;-)

Thank you for the explanations. Yeah...I converted my drum to fire brick this year, so the whole rocket stove is used fire brick. I ran coal in this unit too.I'd say your best bet is to go with fire brick, because after 2 seasons of intense heat, only one brick brick broke, and is still somewhat usable.

to wit, I did a demonstration ..rocket stove , oven, heated bench a year ago for a harvest festival. It 'worked' but, not as well as I had hoped...seems, I 'should have' put refractory >insulative< brick for the initial burn tower (as you show you did, I used brick yard grade firebrick.). Well, I found out, upon demolition, that , that dense of brick, absorbed too much of the initial combustion chamber's heat. I have pics somewhere to upload. It WAS very instructive, as I used to 'hot plate' design for the bake oven on top of the burn riser. But, I had too much soot (carbon) which 'should have' burned up, iffin I'd had the temps above 850F. I'd do that design again, but make the loading/fuel chute deeper, so as to burn 24"-30" wood. A friend in Baltimore, MD has a 44" vertical load capability. Be well, thanks, nk

Do they make a ceramic pipe the right size for this purpose? It seems like it would be more than capable of handling this high heat.

This are the most valuable lessons for us. Shit happens, and i'm grateful for you show us what can happen. On another note, do you plan to reduce the power output of the burner? Seeing what it does with rock, maybe even the firebrick can have a though time in there...

hii Bigelow Brook Farm (Web4Deb), i got one question.. u said u later use brick to temporary replace the melt away riser.. why is concrete being heated up give out black smoke ? ?? i can't figure it out. chimney is suppose to be build with brick for old timer.. why theirs not giving out black smoke ? u r amazing. u made the best RMH video ever.. from beginning to the end... .. thank you for your effort to share your experience.. thank you sincerely. andrew

I figured you would go with cob or ceramic cob=straw, clay, sand..... And burn corn cob or corn stocks.....Great Vids and love to see your setup in person some day......

Last night was hell with a major thaw and heavy rain. My RMH flooded out again. Nothing worse than pumping water out at the same time your burning a fire. I pumped out 60 gallons before I quit. How did your 304 work? Rj

Rob I think you mentioned that you ordered some stainless expanded steel. Can you tell me where you got it from? Thank you. Bob

What about fire brickes in the blast path in order to turbulate the blast stream?

the exhaust doesn't go directly through the plastic pipe. The heat getting into those pipes is only about 150 at most. ;-)

Please inform what the minimum thickness of the wall of the central tube?

Thanks for the great video! QUESTION: If your exhaust flume burned or melted away, why didn't the bottom of the steal drum not get destroyed? What is the temperature difference between these two? I've read that the flume can reach over 2000 F does the temperature drop that much in just 3"? Thank you!

YOU ARE THE MAN!!! Thank You for Sharing!!!

I've been debating making the next one a bit smaller. ;-)

Hi, I really appreciate your videos. Why did you use concrete bricks instead of clay bricks for your temporary heat riser? If I understand your video correctly, even your refractory cement did not fare well? What replacement material do you plan to use? Thanks, Tim

Would vermiculite blocks be of any use, I'm sure that's what's in the back of our log stove

I thought you solved this problem by using a stainless steel flue. Did the stainless steel flue burn away?

Thanks for the detailed info. Very informative. Is there any other kind of heating system that is not so finicky and economical to operate?

I see. Can't say that I'm surprised by the damage. Burning pellets would be like having a bunch of little rockets in a big rocket. Even so, I'd be interested to know exactly what temperatures you DID achieve - has anyone attempted to calculate it?

I replaced it with 6" stainless. It's worth the cost!

Thanks for the info. I just used concrete for some my experiments, but it's all been replaced with fire brick. I"m not sure what the material mix of the bricks but they came from Home Depot. ;-)

How do you know how to do all this building qnd growing?

Just out of curiosity, why were you using pellets? What "problem" were you trying to eliminate? Or were you just experimenting?

the barrel isn't the problem, it's the heat riser....plus if something does go wrong with the barrel, I have access to plenty more for free! ;-)

I have seen guys use Motorcycle exhaust wrap. It is made with titanium or something. I used a fiberglass material used in mufflers and it is getting too hot.

wow iam using a nitrogen tank for my heat riser its 1/2 inch thick whats every one think? not insulated

I ordered some fire bricks since these concrete bricks aren't going make it for the next month. All our cobs get ground up with the rest of the corn and get fed to the cows. ;-)

I thought exhaust pipes had to be above a roof line? It that T section to kill sparks? For some reason I was thinking that must be what the inside of my arteries look like. I had a couple of Dunkin jelly donuts tonight.

That really stinks, you should probably think about containing the amount of fuel you are putting into the system with heat temps over 2000 degrees! Did your Plate that holds up the pellets still maintain its structural integrity? I appreciate the feedback as I'm looking to build one for my house this spring when the ground thaws out.

Concrete is NOT fireproof. Ouch. You are right to prefer fire brick. An example of how bad concrete performs with fire, was a truck fire that happened in NJ, under an overpass. It completely brought down the overpass.

Burn the witch oh it science,,,, Love the vids like always!!! are you going with cob or ceramic? and speaking of Cob do you burn the corn cobs in the rocket mass heater?

Jaimie Mantzel on chanel JMEMantzel discovered a great source for cheap stainless steel vent pipe: chimney liner. I did a quick google search after reading your comment and found 8" stainless steel chimney liner (essentially vent pipe) for $31 a 12'" piece. The site is chimneylinerdepot but it was just the first site I clicked on. Thanks for posting this autopsy! The screenshot kinda looks like a picture from a colonoscopy =)

Perhaps only so much can be expected from old barrels? It seems some of the rocket systems spend a lot on components, spend a lot of time on design, and then hinge it all upon a cheap piece of scrap metal. That's just an observation. One I made a few weeks back looking at other system on Permies.

I just watched a video where the guy used 40% plaster of paris and 60% sand for his gasifier. He claims it should last forever. I researched it and it is considered a high temp mortar.

one complicated beast.

sorry. you can always turn down the volume and read the closed captioning. ;-)

Fireclay pipe will eventually crack...You need firebrick, laid with refractory mortar, and expansion joints every 4 feet at about 1/4", which is generally done with ceramic fiber paper, (it smokes until the organic binders burn out...so be aware of this)Wherever the brick will be close to anything that can burn....be aware the heat transfer in firebrick is enough to catch wood on fire...it must be insulated. I would recommend Ceramic fiber, or Kfac19, both are good to over 1900 C.

You need to use actual ceramic blanket insulation and high temp concrete and make your own bricks. Then use high temp motor/glue paste. I made a 2 burner crucible for melting different metals and is rated for 3,300 f. everything i tried before that was a waste of time and energy, material. I've had an idea similar to this in many was except I don't want to use pellets. When I start making my heater like this I will Just use the high heat concrete, make my own bricks (than I can even mix in perlite or vermiculite) and ceramic blanket insulation. Entry level crete mix is 3,300 f. You do Have to properly cure and heat the bricks for the fist time. After than You are good to go. But you have def saved me A LOT of trial and error, so that I thank you for.

some day it'll invest in a thermocouple and see what the temps get up to. It's quite interesting to see the clay bricks glowing red. ;-)

With all due respect, maybe there is just to much going on with that heating system. sometimes less is more. How big of a bit** would it be to raise the catch basin tank and build a thermal mass bench that wraps around the tank? That way your not having to run at full burn so much. Seems very hot for long periods of time. Too far to exhaust huh.

Better to have it fail in a cheap and easy to replace/modify location, right?

You may need to consider using refractory cement.

If you want it to last you won't get around using Fire Brick. I worked in a foundry a couple of years. Trust me. Invest the Money for good Firebricks and Firecement and you have no Problems for at least 10 Years. Sometimes, when you know a guy who works at a foundry, he can get you the material you need for realy cheap. Or you harvest some Firebrick from an old elektrick night storage heater. And one oter Tip. I recomend you to use a Heat exchanger for your Water heating System. Therfore you can use Radiator Fluid on your Radiators and they will last Forever. And you can place the Heatexchanger somwhere konvinient, so you dont't have to tear down your Heater for maitnance. Look at this that way. How much money can you make in the Time you constantly fiddeling around with the Mass Heater an put in in perspective to the cost of using propper Materials ;-)

you dont think its the black plastic pipe you buried under the floor that might be causing the black smoke do you?when you buried it and said this is what the heat is going to go through to warm the place up I thought that stuff would melt.

you can order online from mcmaster-carr. It isn't cheap!

my respects for the great video's ,just one littel remark for your stianless heatriser it will last a bit longer but will burn treu, Temp in the heatriser can go up to 3000°f ,it would be safer to build the first feed of your heatriser out of firebricks after that the temp go's douwn so the stainless will hold there kind regards

Swap out the rockwool for ceramic fibre blanket

please see my FAQ #4 video about using compost.

im sorry to say, but that you for this failure, now I know to make the entire thing from fire brick, except for things like the heat exchanger radiator ect. also I am thinking of an extra bend in the burn area (where it bends up from the fire pit) in order to maximize on the second burn in order to get more heat out of the carbon gases

How thick was the metal that burned away? How long did it last?

..try using refractory cement, make your compound shapes, and experiment away. Just be sure to burn the gasses (volatiles..) before they cool and condense (creosote). All those 'volatiles' are burnable, and since you've already purchased the wood, why not get all you can out of it, eh..?

The cheapest SS pipe that's 8" was $250. I'm seeing signs of wear in my SS grate so I'd hate to invest in new pipe every few months.

make the furnance with the fire bricks, and the first tube too. it will store some heat too, and last many, many years.