Rocket Mass Heater – Heat Riser Rebuild

Hi Everyone, I have a quick update on the rocket mass heater
since the stainless steel heat riser finally rotted out. Once again, taking a look at the barrel, there
is still some flaking on the top and also along the sides. My guess is that this is
from the extremely high humidity in the greenhouse along with cycling the heater on just once
a day and then letting it completely cool which is condensing a little moisture on it. Looking down inside the barrel, there was
a little ash at the bottom which was expected considering it has run the entire season without
being cleaned. What I found to be a bit surprising were the pieces of stainless steel that were
also in the ash which had blown up and out of the heat riser. Looking down into the heat riser, or what
someone likes to call a “well”, the insulation has settled a little bit, but the stainless
steel pipe has collapsed down nearly a foot. The outer shell of the heat riser, which is
10″ galvanized stove pipe, is in excellent condition. These sections can be used for
other experiment. The rock wool insulation was in fairly good condition along the top,
but had hardened up a little so I disposed of it. It was interesting to see what happened to
the rock wool. The first inch that was on the inner part against the heat had discolored
and hardened, while the outer inch was still soft and looked new. There was a very distinctive
line between the differences. I got about 1000 hours of burn out of this
heat riser so it did surprisingly well considering the abuse I put it through. Once I pulled
the stainless steel pipe out, it became very apparent that there was nothing left to it,
and once again, the rock wool which was exposed directly to the fire had melted. Laying out the remains of the stainless steel
pipe showing the original 5′ of length, this is what was left of it. Now that the old heat riser has been removed
and the base has been cleaned up, it’s time for a new heat riser. I’m finally going to
buckle and install a heat riser made from fire brick. I decided to dado some of the
fire bricks so that they couldn’t collapse into the center. The original heat riser was 6″ which is a
profile of 28.3″ square inches. To minimize the waste of brick, I dado cut two bricks
and then set two complete bricks on their ends. With this setup, the profile area is
slightly less by 2 square inches. Even though it’s slightly smaller, I decided to take the
risk since the heat riser is taller than most heaters and it should have a stronger draft. A cheap wet saw goes right through the fire
brick and it’s brittle enough to tap off any extra material that didn’t come off from the
saw. For the last step, I built a steel cage around
the outside to hold everything in place. Since the steel frame isn’t directly in the blast
zone, it should hold up for quite a while. That’s about it for this heating season. I
have a few more ideas in mind for next year so hopefully I can get them built before we
start heating again. Thanks for watching!

68 thoughts on “Rocket Mass Heater – Heat Riser Rebuild

  1. Critical part for stainless steel pipe seemed to be the lowest section, where apparently was excess oxygen in the burning wood gas. It is not the heat, but oxygen, which destroys the steel pipe. Hope the brick pipe will last longer!  

  2. I find the distinctive line in the rock wool interesting. Why wouldn't it have been gradual? Maybe that too was because of condensation? Anyway, great video. Looking forward to further rocket mass heater updates and your next NUTS as well.

  3. You will find firebrick will work perfectly.  Since I upgraded to firebrick, I haven't had any trouble.  It just works.  You might want to make sure the top of your riser doesn't have anything to capture material.  It should be rounded on top to keep material and ash from building up.  Too much ash and the riser draft will suffer.  I like your design to hold the riser.  I simply used fireplace cement to stack the bricks without any support.  It works, but over time the fireplace cement tends to burn away.

  4. One other thing, I do believe we have an increase death rate of risers because of the humidity in green house domes.  Water vapor is super heated and steam damages the risers.  Metal just doesn't stand a chance.

  5. In the earlier part of the video as you were doing the autopsy, I was wondering if you were going to finally try fire brick. I believe you will find it to be most satisfactory.

  6. That looks like a good solution to your problem I expect it will probably work better than the old one,thanks for posting.

  7. Thanks for documenting all your work, both the good and the bad. I have been following your journey with intense interest and have enjoyed your videos. 

  8. O.K. before you break it in, line the drum w/fireplace tile using fireplace mortar, then like a good frying pan, coat the outside of the drum w/ cooking oil from time to time. When it begins to look whiteish or oxidized, oil it up again. Keep building this "seasoning". It will burn off. I do the same to cast stoves. Let your kids replace it when they're grown and you're retired.!

  9. Are you going to insulate your fire brick as you did the steel pipe and then have another wrap around the insulation? Fire bricks burn out too, they get brittle and crumble in extreme heats.
    I used 6.5 inch well casing as my burn tube and heat riser w/ stainless insulated chimney as the insulation containment. Heat exchanger is a 60 gallon used hot water heater which has a domed top. No rust on exchanger, not sure yet as to the condition of the well-casing. It is still burning great, will autopsy in the spring.

  10. I just have to work for you"Laminar flow". Haha looks good. Hopefully the brakes will last longer and heat up the house gasses as well as the rock wool did.

  11. Just wondering if a length or two of Cast Iron pipe would hold up?  My cast iron coal stove is over 40 years old and looks to be in very good condition.   The advantage of cast iron pipe would be the flanged end that would give a nice seat in a standing configuration.

  12. roll some ospho or phosphoric acid on those rusty barrels, it'll turn the rust into black iron phosphate and the barrel won't rust anymore.

  13. Truly enjoyed your work on the Rocket Stove, great ideas. My question did you use something other than the sand around the barrel to secure it to the brick base? (furnace cement, ect.)

  14. good job with the heat riser frame.  having never used mortar myself, I wasn't looking forward to it and your video seems like a great alternative.

  15. I would install a Steel pipe flat coil at the top of The Riser
    How It's Made – Steam Engines (Shows how to make a 5 Sec Heat Exchanger)
    Between Riser top & the Roof of the barrel
    this internal 2nd combustion hot zone pretty much will can be put to use or even a few uses
    Without any side effect on the Rocket stove

    You have a Coil now making Super Heated STEAM You can now get a few uses out of it

    thermoelectric "Seebeck" modules
    If you feed the super heated steam into a length Square Pipe with these "Seebeck" modules in Sting stacks of 4x and cool the other side (Waterblocks) and and have more of these String stacks in parallel for the entire length of Square Pipe you should be able to feed the power they make into a MPPT Charger your Battery bank and RUN LED Grow lights & Fans (Extended light growing hours Any season Full production Growing)

    What to do with the Hot water from the Square Pipe Well you can use this water to
    Run a Bio Gas Digester The Gas you make can be Stored & used to Help ignite the rocket stove, cook or a Generator (Old plants, Excess plants,  Wasted food, Human Waste, Fish Waste, dead fish can be digested down to gas + rich soil fertilizer (Sell this off))
    Another use is put air ducts under you solar panels and Hot Air Blast them to remove Snow & Ice (use a Car rad and Fan but make it so that it drains so it wont freeze up when not being used)
     any warm water left over can warm the fish water

  16. I am not the best of health or energy these days, I found 8 inch diameter flue liner works nicely as the heat riser. For older women, it's easy and quick.

  17. 6" steel well casing is pretty thick pipe. Perhaps it could be used as the riser? I saw the conversation below wondering about cast iron pipe, and the lack of availability.

  18. This is a crazy project, but i really like it.
    I started watching the series because of the dome video,
    now i'm here watching rocket heaters.
    Fun project, your green house,
    i could watch it all afternoon, in fact i did. LOL

  19. I have watched all of the Videos in your rocket stove series and many others from People claiming to be experts in the field. Some mention has been made of temperatures over 3000° in the heat riser! With all of the improvements you have been making, I have no doubt your stove is producing such temps. And that is the area where you have found the materials failing.

  20. @Bigelow Brook Farm (Web4Deb) 
    I'm very excited to see updated video on this build; hopefully a completed summary with pictures of the updated pellet feeder and grate design, draft flow pics & diagrams, changes you've made to the water heater radiators, etc. This is an amazing setup. Congrats!

  21. Im really REALLY looking forward to hearing how this latest modification worked out for you.. Good Luck and good growing 🙂

  22. could you do an update on the new heat riser, i would like to build one to heat my brewery and would like some more build specs to help me

  23. It is realy nice ipece of work you have done. Have you concidered using fire clay tube for heat riser? It could last ages and you wouldn't have to build any steel support for it.

  24. Just wondering. Did you teach yourself all these hvac skills and construction or are you drawing on an hvac or steam ticket background?

  25. Found him on facebook, his name is Asuka Banno and he was making them out of clay waste pipe, hes got a facebook page called rocketstovetk, interesting experiments, i wont be throwing any more old pipe into the skips anyway!

  26. just something that may work for the pellet grid how about useing thin terra cotta tilles on their side ,they should last longer if they don't crack on the first burn , just   a wondering 😉
    if they are supported from the underside i think the support would live longer
    kind regards karl

  27. Really like the fire brick idea for this!   Your engineering is a welcomed and thought provoking!!!  I have watched dozens of home models for rocket stoves..YOUR entire system appears to be user friendly version and detailed for home or greenhouse.
    Great job sharing the ups and downs to make things work!
     I KNOW you are busy, but can you give an update on how it ran / worked for the 2014-15 winter????

  28. Thanks for sharing your progress.Was wondering if you insulated the outside of your burn tube.I am building a system slimier to yours with a fire brick burn chamber and burn tube and was hoping that I could get away with not insulating the burn tube.Would be interested in your thoughts, Cheers

  29. As I watched these excellent videos I thought why not use clay flue liners. After some research they may work but can crack and split due to rapid heating of the liner. 

    You've contributed a great resource of information on rocket stoves. Keep up the good work!

  30. So rust is a serious problem. Have you considered using a sacrificial anode rod like they use in conventional water heater? It would save time from rebuilding a new heater every now and then. You only need to replace the rod. Same method is used on ships and oil rig platform.

    Edit: I've looked it up…an anode sacrificial rod lasts about 3-10 years and costs less than $50. There are also discussions on a few permies forum of adding zinc/brass plates to the component as sacrificial anode.


  32. How has the fire brick stack worked for you? Did the sand act as a good mass for storing heat? How long was your underground run?

  33. Thanks for telling us that you got a thousand hours of burn time out of the stainless.
    That was important to know.
    Amazing what the heat will do to metal.

  34. I used fire brick on my horizontal gravity fed rocket stove and it's held up very well now for 3 years. I heat my home with it so I need it to be dependable. I've burned several times so the brick turns red hot and it hasn't broke down yet. There are a few flakes coming off some of the ones in the direct flame path, but they are still intact for the most part and will not need to be replaced for the 4th year burn season, which I'm into now. As I'm posting this, the temp outside is 26 degrees and the stove is running around 550 degrees now and it is 74 degrees in here, which is perfect. A bag of hardwood pellets (40 lbs.) will last around 9 – 10 hours at $3.99 a bag, so I'm pleased with the cost of heating with them.

  35. If you held the heat riser with refractory cement or clay around the perimeter you might find it will last much longer. You could even use chicken wire inside the clay to help make it reinforced.

  36. Hey- we have a problem with our heat riser and would appreciate some posible advice and suggestions.
    Inside the barrel, the insulation for our heat riser will not stick to the pipe- the insulation material, when it is dry, crumbles off the pipe and clogs the entrance to our manifold. I see here you have an outer shell. What materials did you use for your insulation? Ash, perlite?
    Thinka you. good building (:

  37. ok, this was super informative!!! i plan to install a rocket mass heater in my cabin…i got 6yr before i can move there; plenty of time to work out the kinks…i plan to use rigid ceramic fiber board; easy to cut and rated for 3000…the "erector set" metal i saw here is a really good idea…btw, my place is in hardy, arkansas…so…would you consider helping me via hangouts, email, whatever is effective? i got a trip planned in april so right now i'm just focused on that…but hopefully by september i can start building models…

    i'm not asking for freebies…if you have a rate plz let me know

  38. So you got $500 of firebrick or did you find a deal? All the ones I see are very expensive. I think you could've done this cheaper with either vermiculite board or ceramic fiber board. This comment is more for people looking at buying some firebrick, as I just learned about those board materials and plan to use them for a rocket stove build 😉

  39. Building a steel frame for the fire brick and dado-ing the corners of the bricks to keep them from falling in, is very robust and the frame should last pretty indefinitely.

  40. Would a RMH keep a winter greenhouse in middle tennessee in the 70F range? Its a prefab plastic lined 10X20X7.5.

    Trying to figure out my heating and its driving me nuts. The greenhouse will hold several barrels of water with fish in them. I could run pipes through a sand bed/walkway, would that help keep the temps that warm? My WATER has to stay, at the coldest, 70 degrees.

    I do not want to run the heat pipes in a hard to access way.

  41. Make your own refractory cement and fire brick. You can mold it as you want. Waterglass, (sodium sillicate),, sand and perilite. You can make your own water glass too as I did and it worked the first time!

  42. Yes the other commentators mentioned the 2000 degree resistant caulk you can squeeze from a caulking gun & dispense with the steel frame

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