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rocket mass heaters

rocket stove and butt warmer

Erica Wisner

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posted 14 years ago

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Tinknal wrote:
I've seen concrete pipe used in sewer installations. It comes in a variety of dimensions and I think I could find one the right dimensions for the heat riser. Any opinions of this?

High heats tend to eat the lime out of cement, making it powder away over time. Better to use refractory materials or old ceramic chimney liners, if you can find them.

Len wrote:
The inside of the riser should be no larger than the burn tunnel.... I would suggest the riser should be the smallest diameter in the whole system.... This doesn't really make sense as the gases are hottest there and so take up the most room, but that is what works. ... Best if burn tunnel and riser are the same CSA...

Patio slabs, they come 18x18 to 36x36 (at least here) two layers would cover the cracks between them and they add mass right where you need it to keep your beds from over heating and to extend the time between burns.

Try fixing 3 above first... I have seen systems with a big space between riser and barrel that still seemed to work.

Go with the same cross-sectional area throughout, EXCEPT the downdraft area inside the barrel and manifold can be substantially larger. Low-pressure here helps keep the draft cell working well.

Warning: making heat riser smaller than burn tunnel can cause smoke-back problems. Only reason to make the burn tunnel larger is to make it very slightly taller to accommodate one day's worth of ashes on the bottom - don't add more than about 5 square inches, unless you plan to have some extra draft/air controls.

Same cross-sectional area throughout is most effective rule of thumb, and not that hard to achieve.

Re: moisture protection:
We've built these in garden beds where the soil itself was the thermal mass, with some rubble on top of the pipes so you don't accidentally puncture them with a trowel. Moisture will rust out the pipes over time, but it will take years. You could also build a brick box instead of using ducting and cob, for a more permanent installation under damp conditions.

If you do go with cement slabs, make sure they are tilted slightly for drainage, and that both top and bottom have a way to drain and wick away moisture. Otherwise the cement will just trap moisture on both sides, and you have turned a short acute problem into a chronic one.

Could also try roofing tiles, which are designed for the purpose. Or any form of tile, you can set them into the top of a cob mass, and make channels with different-height units and slopes, to allow water and air to flow away, yet keep the planting trays level.

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posted 14 years ago

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Thanks Erica. I suspected that the heat could damage the concrete in some way but I had to ask. I suspect that maybe a riser with about 2 inches of asbestos would be optimal. Of course that kind of material would be hard to find now and would create other potential problems. I spent 3 years in the asbestos abatement industry and I'm thinking of all the different materials that got thrown away (including tons and tons of ordinary fire brick).

Len Ovens

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Tinknal wrote:
I've seen concrete pipe used in sewer installations. It comes in a variety of dimensions and I think I could find one the right dimensions for the heat riser. Any opinions of this?

concrete will not stand the heat. It looses its strength at around 700C and does not recover when cooled. could be used in the mass part though.

Erica Wisner

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Tinknal wrote:
Thanks Erica. I suspected that the heat could damage the concrete in some way but I had to ask. I suspect that maybe a riser with about 2 inches of asbestos would be optimal. Of course that kind of material would be hard to find now and would create other potential problems. I spent 3 years in the asbestos abatement industry and I'm thinking of all the different materials that got thrown away (including tons and tons of ordinary fire brick).

I don't think they're gonna let asbestos back on the market anytime soon. If you still like the stuff after removing it, you must have some good tricks for keeping the dust down and limiting exposure. Care to share any?

If I had an unlimited budget / scrap pile, I'd play with kiln brick.
Maybe with a light earthen plaster, or spray-coat of ceramic, around the exterior to protect it for cleaning days.

Or refractory cloth, which might be able to wrap other materials (like cement) that wouldn't stand the heat alone. Not sure how long-term temperature protection it gives.

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Erica Wisner wrote:
I don't think they're gonna let asbestos back on the market anytime soon. If you still like the stuff after removing it, you must have some good tricks for keeping the dust down and limiting exposure. Care to share any?

Well Erica, the trick would be to encapsulate it. In this application I would put it in a double walled cylinder and weld it shut, with maybe a few small holes to keep it from exploding. It really is a great insulator. I've seen steam fittings with 2 inches of asbestos on them that were room temp to the touch that after removal it would met plastic from a foot away. I would think it would be perfect for providing that heat differential on the inside and outside of the heat riser. As deadly as asbestos can be you need to be aware that we are all exposed to it every day, and have been our entire lives. The key is to limit our exposure.

Erica Wisner

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Tinknal wrote:
Well Erica, the trick would be to encapsulate it. In this application I would put it in a double walled cylinder and weld it shut, with maybe a few small holes to keep it from exploding. It really is a great insulator. I've seen steam fittings with 2 inches of asbestos on them that were room temp to the touch that after removal it would met plastic from a foot away. I would think it would be perfect for providing that heat differential on the inside and outside of the heat riser. As deadly as asbestos can be you need to be aware that we are all exposed to it every day, and have been our entire lives. The key is to limit our exposure.

(Brief internal rant about Those People who panic over 'named villains' like asbestos and mercury, but are largely ignorant about actual risk factors. Ignore instructions on drain cleaners, for example, or gamble their health on basic hygiene choices like breathing dust and drinking stagnant water.)

I've heard from people who worked with asbestos when it was the gold standard; 'asbestos' meant 'fireproof' and one guy described his heat tolerance as 'asbestos hands.' I think the intensive abatement programs probably caused a lot more acute exposure than leaving the stuff in place, assuming it was installed reasonably well.

Limiting exposure - same goes for masonry and ceramic dust in general.
We always wet down earthen masonry, and other masonry if needed, to limit dust.

Perlite dust is nasty, tiny volcanic-glass shards. My understanding is asbestos is dangerous for a similar reason, the super-fine fibers can travel deep into the lungs. Fiberglass is a third similar material. (And I would guess that some zinc salts are too - the crystal structure on those is very needle-like.) Any good mineral insulation is likely to have this property, to some degree.

We stabilize perlite with liquid clay slip, and I always get it damp before working with it. If it needs re-working, I'd wet it again before removing. Hard to get everyone in a workshop into dust masks for a 15-minute job, so we try to eliminate the dust instead.

I was wondering if you had tricks like that for asbestos - like a recommendation for a respirator, or for limiting dust. Encapsulating seems like a decent way to limit exposure for the useful life of the object; it's the building and teardown where exposure is most acute.

Are there still commercial applications where asbestos is considered best practice, since the alternatives are worse?

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Erica, yes, when working with it (which anymore usually means removing it) the basic rules are encapsulation, containment, usually in a negative air HEPA filtered enclosure, respirators, and amended (soapy) water. It can be repaired and left in place and often is, but any time that reconstruction occurs it generally has to be removed if the construction process is going to disturb it.

I know it is still used in brake pads and I'm pretty sure that it is used in other applications but I'm not sure what they are.

The dangers are Asbestosis. It gets in the lungs and the body recognizes it as a foreign object and attacks it. It creates hard plaques in the lungs. It is always fatal.

Mesothilioma, a cancer of the lining of the lungs. Also always fatal.

Lung cancer.

The latency period of asbestos related diseases is 10 to 40 years, which means that it can show up 10 to 40 years after exposure.

Clifford Reinke

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OK I have started construction. Here is a time lapse video of what I did today.

http://www.youtube.com/watch?v=NtX0B00qIeA

Cliff (Start a rEVOLution, grow a garden)

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posted 14 years ago

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careinke wrote:
OK I have started construction. Here is a time lapse video of what I did today.

http://www.youtube.com/watch?v=NtX0B00qIeA

I am just amazed at how you got all those people to work so quickly. What kind of coffee did you feed them?

Clifford Reinke

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LOL, Tomorrow I will have my son take 4 pics per minute at 4fps that should slow it down a bit. This one was taken at 4 pics per minute but the frame rate was 15fps. A little fast

Cliff (Start a rEVOLution, grow a garden)

Clifford Reinke

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Location: Puget Sound

posted 14 years ago

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Actually got to light the stove today! It draws (pushes?) very well. Now to work on the mass storage.

Lessons learned:

1. It's easy to add too much water to your cob mixture.
2. The video gets boring when you are off making cob.
3. Pyrex cake pans explode!!!

Video:

http://www.youtube.com/watch?v=W3cs4uZpufc&feature=player_embedded

Cliff (Start a rEVOLution, grow a garden)

Erica Wisner

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careinke wrote:
Actually got to light the stove today! It draws (pushes?) very well. Now to work on the mass storage.

Lessons learned:

1. It's easy to add too much water to your cob mixture.
2. The video gets boring when you are off making cob.
3. Pyrex cake pans explode!!!

Video:

http://www.youtube.com/watch?v=W3cs4uZpufc&feature=player_embedded

Yay! You folks must be freezing in this winter weather.

Ernie says nobody believes him about the Pyrex - they spent about $300 on a big piece to do a cut-away version, and it lasted about 30 seconds before the whole thing shattered.

Stove glass doors are insulated from the rest of the door, and air-cooled by a wash of air falling from a small air intake, so they aren't exposed to as much thermal contrast.

I still believe it can be done... but it's going to take some clever engineering, and materials (and tools) that I can't afford.

-Erica Wisner
http://www.ErnieAndErica.info

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posted 14 years ago

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mica

Erica Wisner

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posted 14 years ago

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wardd wrote:
mica

Worth trying; haven't found a piece of mica big enough to try it yet...

Erica Wisner wrote:
... that I can afford.

Got a source? We can give you a discount coupon for us or Cob Cottage workshops, if you have a source for mica in large sizes that we can play with.

-Erica Wisner

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glassceramics
Thermal shock resistance °C 800

The industry of fireplaces is for decades our most important partner. It is a very profitable relation for us and also for our business partners because at all times for the company HECKER the needs of the customer play the major role.

CERAN
ys
-auer-

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Erica Wisner wrote:
Worth trying; haven't found a piece of mica big enough to try it yet...
Got a source? We can give you a discount coupon for us or Cob Cottage workshops, if you have a source for mica in large sizes that we can play with.

-Erica Wisner

don't know what you mean by large, these are for kerosine heaters so 3 1/2" x 4 "

i have ordered wicks from them in the past

http://www.milesstair.com/accessories.html

i know nothing about the following

http://www.reliancemica.com/Products.htm

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Here is a first draft of my planned system. It is an overhead view. I'm sure there will be many revisions, this is just a starting point. I highly encourage everyone to trash, dis, and generally scoff at these plans, as long as you have viable improvements or suggestions.

Thanks, Big Al

Untitled.png

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Just a note to clarify. The duct ( yellow lines) would lie above to exhaust (silver lines).

Erica Wisner

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Tinknal wrote:
Here is a first draft of my planned system. It is an overhead view. I'm sure there will be many revisions, this is just a starting point. I highly encourage everyone to trash, dis, and generally scoff at these plans, as long as you have viable improvements or suggestions.

Thanks, Big Al

Let the dissing and scoffing commence!

Actually, not a bad plan.

Since you have combustible walls and floor, I would suggest a larger air gap between the stove and these elements. I would like to send you pictures of our recent project along these lines, showing how we used channels in the footing to move air below the stove. (But our photographer is making a video from them, so they may not be available for a while.)
The channels underneath would let you leave the top surface exposed for good sit-upon heat availability, and a way to collect warm air for venting to other parts of the house.

ASTM specs for Masonry Heaters specify a minimum masonry thickness of 8", and a minimum gap to combustible walls of 4" (with a 4" stem wall allowed where needed to bridge gaps for structural support).

In our experience with cob, a minimum thickness of 4" is workable (heat conduction is slower than with cement masonry), but 5-6" is better on an 8" system. Insulative layers with Perlite-clay or Perlite-cob can be included to reduce heat conduction to unwanted areas, and encourage the heat to stay in the bench or roomward surfaces.

It's OK to have a very small cob thickness in the middle, 1-2" between the ducts is workable, though more thermal mass gives more heat storage.

Given these constraints, I think if you want the triple-pass in the section nearest the combustion, you will need to go up vertically to fit all the pipes in the bench with good clearances. Making it a single-pass here could work fine, especially since this is the hottest pipe and will heat a good thickness of cob.

Hope that helps.

We are considering selling as-built drawings for successful systems online. Would you be interested in a good drawing of our recent stove that is similar to your proposed project, if it included all these clearances, materials, and techniques?

-Erica Wisner
http://www.ErnieAndErica.info

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Erica, I would be interested in any information you have. I was thinking that with an air space rather than an insulated area around combustibles (bearing in mind that the combustibles are covered with drywall) that 1 inch would be sufficient.

Bear in mind that I live in a location where codes are not as stringent ( read nearly nonexistent) as you are accustomed to.

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Erica Wisner wrote:

Given these constraints, I think if you want the triple-pass in the section nearest the combustion, you will need to go up vertically to fit all the pipes in the bench with good clearances. Making it a single-pass here could work fine, especially since this is the hottest pipe and will heat a good thickness of cob.

-Erica Wisner
http://www.ErnieAndErica.info

Erica Wisner

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Tinknal wrote:
Erica, I would be interested in any information you have. I was thinking that with an air space rather than an insulated area around combustibles (bearing in mind that the combustibles are covered with drywall) that 1 inch would be sufficient.

Bear in mind that I live in a location where codes are not as stringent ( read nearly nonexistent) as you are accustomed to.

We've seen non-permitted installations with a 1" or 2" insulation layer to protect drywall, and no air gap, and over a couple of years' use there were no problems.
The main risk would be an undetected hot spot, like if a duct got shifted during the build to within 2-3" of the masonry surface.

One reason for using the 4" standard is that it's pretty easy to reach down there or use a vacuum hose or broom to remove any clutter that might fall in. If it's only a 1" gap, debris and dust get wedged in there and create various problems.

Of course, if you use a screen, or your hot-air collection duct, to cap this area, then less stuff would fall in.

Here's an as-built drawing of an ordinary 6" diameter system, using perlite insulation for the drywall sides, and built on loose fill over a concrete slab floor.
Took me a couple of days to draft this, with advice from an architect friend.

(The drawing and a photo of the stove can be seen on our website, at https://sites.google.com/a/ernieanderica.info/www/rocketmassheaterpermitting )

We're going to do a drawing or CAD model at this level of detail, showing a design we used for installation over a wood floor in a conventional stick-frame house. (It's part of our instruction video project, and I want to show clear cutaway views that can be included in the film.)
With construction details and references, and given that maybe a few people per year might want to buy the drawing, what do you think might be a fair price?

I'm not asking you to commit to paying me for the drawing, but please give me some feedback about what price would reflect the value of the information to someone like yourself, who is ready to build one of these devices.

For that matter, everybody else feel free to suggest a number also.

We're thinking about doing design services this way:
Instead of negotiating with each DIY builder, we just put out detailed drawings of as-built stoves that work well, kinda like the way boat plans are sold online. Basic concept and attractive photos for free, paying customers get construction details and accurate dimensions.

We would distinguish between proven as-built designs, and proposed (unproven) designs. So my drawing of the stove we already built might be useful to you in designing your system. If I was to draw your proposed system using the techniques I have in mind, it would be classed as 'unproven' until you built it and liked it.

Eventually, we'd collect enough proven designs to fit almost any situation, and builders could proceed with confidence and just adjust the surface details like tiles and colors.

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Erica, I would love to have a custom designed system. The trouble is that if it cost a nickle to shit I would have to throw up.

Clifford Reinke

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Location: Puget Sound

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Erica,
There is one guy on the web selling his plans for $35. It is for an all brick design for the stove. I know at least one person who bought the plans (not me).

Cliff (Start a rEVOLution, grow a garden)

Erica Wisner

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Tinknal wrote:
Erica, I would love to have a custom designed system. The trouble is that if it cost a nickle to shit I would have to throw up.

LOL. Well, good thing you're smart then.
I don't think you need a custom design, and you are likely to pick up anything useful from our recent design from a basic description. I'll let you know when I have the basic drawing up.

I wouldn't expect to sell too many plans to the folks on these forums, as everybody seems to have their own ideas. But some people will pay to avoid the hassle of the experimental learning curve, especially if they are busy and in the "time is money" mindset.
Some folks don't need the "why," just want something to work right the first time, and be able to plan it step by step with a budget and timetable.

Ernie can build a boat from "study plans" if he wants to. But if he sees a good design with time-saving cut plans and construction details, he will spend the money.

Good plans save time, and sometimes materials; reliable information could have saved us at least $70 on our last boat, plus about 2 weeks' labor, on failed experimental materials.

careinke wrote:
Erica,
There is one guy on the web selling his plans for $35. It is for an all brick design for the stove. I know at least one person who bought the plans (not me).

Thanks for the reference. I think I know the guy you mean.

-Erica

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Erica, I looked at your proposed building code. Very nice. Clear and concise and easy to understand. I think that a simple illustration of a system with the components labeled and named may help folks who haven't seen a system understand it.

I would suggest one small edit under 5.4.4

hummus is chick pea paste.

hummas is decomposing organic material

Of course it would prolly smell good while curing if you threw a little hummus in the cob mix.......

Clifford Reinke

Posts: 124

Location: Puget Sound

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Erica Wisner wrote:
LOL. Well, good thing you're smart then.
I don't think you need a custom design, and you are likely to pick up anything useful from our recent design from a basic description. I'll let you know when I have the basic drawing up.

I wouldn't expect to sell too many plans to the folks on these forums, as everybody seems to have their own ideas. But some people will pay to avoid the hassle of the experimental learning curve, especially if they are busy and in the "time is money" mindset.
Some folks don't need the "why," just want something to work right the first time, and be able to plan it step by step with a budget and timetable.

Ernie can build a boat from "study plans" if he wants to. But if he sees a good design with time-saving cut plans and construction details, he will spend the money.

Good plans save time, and sometimes materials; reliable information could have saved us at least $70 on our last boat, plus about 2 weeks' labor, on failed experimental materials.

Thanks for the reference. I think I know the guy you mean.

-Erica

Erica,

My brother in Law (and neighbor), after seeing the rocket stove asked if you could get plans for it. He basically repeated exactly what your saying. He said he knows I like the math, science, and tinkering, but lots of people don't care about the theory, they just want to build it. He has built boats from detailed plans and thinks a price of $200-$300 would be reasonable.

Of course that would include materials list, some scale drawings, and a video. I would suggest in your materials list you include both the triple insulated riser and the cheaper perlite insulated riser.

Cliff (Start a rEVOLution, grow a garden)

Jim Argeropoulos

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As I've said to Ernie before. The tinker people here wouldn't be interested, but I think once the stove has passed testing, there will be a market for a combustion chamber kit.
Plans/video are a good option too.
I'm too cheap to plans, but I would consider attending a class if there was one within reasonable driving distance. I'd much rather put my hands on and ask questions.

Erica Wisner

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Silver wrote:
As I've said to Ernie before. The tinker people here wouldn't be interested, but I think once the stove has passed testing, there will be a market for a combustion chamber kit.
Plans/video are a good option too.
I'm too cheap to plans, but I would consider attending a class if there was one within reasonable driving distance. I'd much rather put my hands on and ask questions.

Thanks very much, Tinknal and Careinke, for taking the time to offer more detailed comments.
The "my dad's friend said" review is a type of feedback I totally appreciate, as these are people I would rarely hear from directly.

I thought we caught the "hummus" on the last edit! Fresh eyes are so important.

Silver - Thanks for the reflections also.
We think as you do, that the hands-on experience answers more questions (including the ones you didn't know to ask) than any written guidelines or instructions.

I'm excited to find out what our videographer can do with the clips he's got from multiple workshops. Good video is probably the next-best thing to hands-on practice.

I think you're right about the testing. We are currently fund-raising for independent lab tests.

Once we have official approval available, I'd like to run extended apprenticeships for installer/contractors, so they get a full range of hands-on training and theory. They can take the video home for a refresher, but I want the critical errors to be real for them and not just blah, blah, blah...

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Silver wrote:
... I would consider attending a class if there was one within reasonable driving distance. I'd much rather put my hands on and ask questions.

You on the East Coast?
We get as far as Toronto in April, probably going back again this year.
and we may be trying for a workshop in Massachusetts or New York one of these years. We could use help to get it onto the right mailing lists, or send promotional materials for people to circulate on our behalf, to ensure that the trip could pay for itself.

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Can the exhaust be split? This would eliminate a lot of headaches for me. How much would you have to step down the split portion from the full diameter portion?

This illustration is not to scale. Assume an 8 inch system here, but if a different size would be better please speak up. This would be about 24 linear feet, or about 46 feet counting both exhausts.

ehhaust-revision.png

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What you have to be careful of in a split is to be sure that both exhaust pipes are both exhausting. By joining them back together near the end I think would ensure this happening. I think your design will work but not sure on the math with the step down. If it were me, I would probably go from 8" to 6". I don't think that you can go wrong with bigger exhaust.
Hope this helps.

Len Ovens

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Tinknal wrote:
Can the exhaust be split? This would eliminate a lot of headaches for me. How much would you have to step down the split portion from the full diameter portion?

Take a look at the pictures in the thread called:

"rocket mass floor heater -- finally completed and it works!"

Where they split to four runs. The caveats are, no guarantee of even division of flow and comes heavily not recommended by those who have built lots of RMHs. Basically this does not mean it will not work so much as you are on your own and should be willing to test it in a few different configurations outside before building it in. Oh, and then share what you found once you try it

I am in the same position. I want to try some things (splitting path through mass is just one of them

) Normally, you want to have constant CSA throughout. CSA for 8inch round is 50sqin so two 6in runs might work (28sqinch each for 56sqin total). After you rejoin, to 8inch again, a straight run may help. I personally think (but have yet to try.... I have built and fired up to the top of riser so far) that the smaller pipes should be a bit big to make up for increased resistance to flow due to larger total circumference.... experiment!

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yeah, I will have to agree with that. The going back to 8" for a bit of a run I believe would balance the draw out between the two pipes. Of course, you could always run one pipe all the way down and then back again and then all the way back down making a little wider bench to sit on or to lay on. This would give you a continual run.

Erica Wisner

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posted 14 years ago

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Foxfire7893 wrote:
yeah, I will have to agree with that. The going back to 8" for a bit of a run I believe would balance the draw out between the two pipes. Of course, you could always run one pipe all the way down and then back again and then all the way back down making a little wider bench to sit on or to lay on. This would give you a continual run.

The successful split runs I've heard about (I know of two, including the one on the other forum here), are both a large number of separate pipes that don't rejoin.

I'd be concerned that rejoining the pipes might reinforce the "either, or," nature of the flow, and make it harder to do crude manual adjustments for even flow by retro-fitting a partial damper. Then again, you don't really want to risk damping these systems down too far anyway.

A bigger question is going to be, which direction is the prevailing wind? Because whichever option lets you put the tailpipe downwind, instead of where it will get blown into, is going to work better. Mock it up in place, after all the outdoor trials, and fire it before putting cob on, to see if you need to reconsider.

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posted 14 years ago

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The prevailing wind would be a good news/bad news situation. It would exhaust into the prevailing winds, but the home is well sheltered in that direction and we rarely feel them. I could put 10 foot riser indoors or out and get above the roof line.

Clifford Reinke

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posted 14 years ago

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I am trying to find out what a "normal" temperature range is for the barrel top when running your RMH. Mine seems to like to run right around 450 F. Although I have had it up to 800 F. It seems that when it gets above 600 F the fire starts to creep up the sticks and I have to let it burn down before adding more wood.

So if any of you have been taking temp measurements I would be interested in your results.

Thanks

Cliff (Start a rEVOLution, grow a garden)

Erica Wisner

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posted 14 years ago

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careinke wrote:
I am trying to find out what a "normal" temperature range is for the barrel top when running your RMH. Mine seems to like to run right around 450 F. Although I have had it up to 800 F. It seems that when it gets above 600 F the fire starts to creep up the sticks and I have to let it burn down before adding more wood.

So if any of you have been taking temp measurements I would be interested in your results.

Thanks

Our 6" system with a small barrel (15" diameter) runs about the same temperatures as a woodstove along the top third of its surface (400-700 degrees F). Cooler below, usually warm to the touch but sometimes hot enough to hurt. When it's hottest, it draws faster in our case.

Ianto's 8" system with a 25" barrel tends to run hot enough to simmer water on top, and warm enough to touch about halfway down.

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posted 14 years ago

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Hey all. I'm new hear but love the idea of these rocket mass heaters. I've read alot and watched all the videos but didn't see anything about the local laws and rules about the rocket stove. Just wondering if i plan to build one can you get the permit from the county or do you need to just do it under the radar? I live in Idaho Falls Idaho. I'm building a cabin and I'm planing to use a quanset style steel building for the exterior. I was thinking that this heater would be perfect for this cabin. Well let me know what you think. Thanks Pat

Clifford Reinke

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This Rocket Stove for my greenhouse is a lot more labor intensive than I thought it would be. Anyway, here is a video of my progress so far:

http://www.youtube.com/watch?v=w5hNIvnZ51I

It is pretty amateurish, sorry about that, but it also shows a little of the main garden area.

Cliff (Start a rEVOLution, grow a garden)

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