rocket stove and butt warmer

not that we know of. if there is some interest in another workshop for that area later in the summer and the dates work out Erica and i would love to head back up.  Josh would like to have us do these every year and i think he would be open to two a year if there was sufficient participation. or you could organize a workshop yourself closer to/at home. Either way Erica and i like the area so its not hard to get us to come for a visit we would even consider a winter workshop if it was in a space big enough and warm enough to have liquid water and room for mixing cob.

better we travel then a bunch of folks so if we have an audience we try to be available.

For interest sake

http://www.treehugger.com/files/2010/03/rocket-stoves-haiti.php

Back to technical questions.  I like the idea of the foil tape seal.  Do you have to put heat through the partly completed stove to dry the cob for it to adhere?

nope the aluminum tape is the same stuff sold in hardware stores for sealing house ducting. made by 3M i think; sticky on one side.

if you wanted to just use sheet foil you could make flour paste glue and get pretty much the same effect.

That's the tape I was thinking of, it sticks to the metal pipe and the WET cob??

hmm i think i am missing something here.  only thing needing to be sealed is the joints in the ducting.

I was asking originally about where the ducting meets the cob at the exit to the ash pit.  In the pdf the diagram on pg 48, and the ash pit to the mass heater portion on pg 62 where the ducting for the mass heater comes into the junction between the heat riser barrel exit and the thermal mass bench.  The aluminum tape for the metal to metal ducting junctions in the bench aren't a problem.  It's where the 2 dissimilar materials have to seal with each other that I'm wondering if there is a trick to.

not really the best seal you will get in that junction is slip clay with a good amount of fine sand. but that area is buried rather deep in the structure and the flow is such that IME you wont have any gas out problems. if you have a worry about it you can index the bottom third of a 55 gal drum to fit over the combustion area and use it as your manifold allowing you seal the join. you do still need to pay attention to your cross sectional area. as the exhaust passes the join between the two barrels. Let me know if this is un clear to you and what parts are un clear so i can try to explain it out for you. until Erica had seen me do it she didnt get it so its possible she can put it into words that will work better

Nope, I understand.  Barrel 1 as normal, barrel 2 cut and shaped to extend to the edge of the ash pit.  Cut a hole in it and cut the exhaust pipe to shape, like indexing a log to log joint in a log house or the pipe in a bicycle frame.  Join the exhaust and drum then seal the joint with metal tape.  Also seal the joint between drum 1 and drum 2 with metal tape and cob over the joints.

yep thats the ticket.  thanks for the recap in different language.

this method can make the job a little more complex but not overly so. i like doing stoves this way cause i think it makes for a cleaner install and i have more control over air leaks.
hmm one consideration is the thermal cob that surrounds this needs to be pretty high grade. do test bricks to make sure your bricks do not crack. the drum section will expand and contract so you want the cob around it as strong as possible.

Oh I'm a happy boy, out shop foreman was cleaning house and threw out 5 brand new rolls of industrial grade 2" x 60 yard foil tape.  Happy, happy happy!!!  As well, I have found a local source for used fire brick at .50 each.  School ends in 3 months, I'm just collecting all the stuff I need for my rocket mass heater so's I can make it happen this summer.

chris

I have been tinkering with the idea of a rocket stove/russian fireplace for awhile now. I was thinking of using a wall in my basement as some of the mass. Possibly digging down and installing blue board insulation on the outside below grade. Then building a secondary wall on the inside with the pipe between the two, using crushed stone and sand as mass between the two.
I assume people use the cobb because of low cost and being readily available but do they also use it because it has a resistance to cracking from the heating and cooling cycle?. I live in a city with a very sandy soil. If I built this it would be out of block, brick and mortar. I know (or think I know)  that the added thermal mass will help even the temperature swings to lessen the thermal stress. Am I right?
Thoughts ? Comments? Ideas? References?

I would start with reading the rocket mass heaters book it can be found here at www.rocketstoves.com in both paper and PDF. there will be a third edition out soon with new research included.

our research suggests that sand is not a good thermal mass by itself as it acts more as an insulator. (think of a beach in the hot sun and how the heat only penetrates an inch or so. same with gravel  the top layer gets hot fast and the deeper stuff only heats very slowly. the reason for a plastic material like cob is that it is hand moldable and is a continuous mass so it heat transfers pretty well. in any place other than where the fire actually is the thermal shock is not an issue.

Again please read the book it answers allot of questions.

Ernie,

Any cool stuff you can tell us about the third edition?

I don't suppose you want any reviewers and the like?  Like, um, somebody at, say, my level? 

Cool stuff will probably be water heaters and the like. I am not the person to ask about cool stuff we will try to get the stoves approved here in portland and in the book. along with methods and such so folks can start the process in there own area. some more refinements to the build and probably refine some terms so we can use language specific to RMH installs. might be a hydronic floor (linked system with solar hot water heater) in the book as well if I can find the time to put it in and proof it. (this is why we run work shops, it makes thing go faster and it funds the research so we can actually do stuff)

for proof reading and such you will have to ask Ianto and Leslie about that.

anyone ever heard of a kang?  seems somebody beat eco-weirdos to the mass bench idea by around two thousand years.  maybe the kang connection is already widely-known in this crowd, but it was news to me when I stumbled across it today.

anyhow, made me wonder: could you build the mass, including the flue, entirely out of bricks?  I don't know that there would be a good reason to, but would it work?

how about building the flue out of bricks, then covering that with cob?  bricks are likely to be more expensive than galvanized duct if you don't know of salvage opportunities, but I could see some advantages.

hell, could you build the whole thing out of brick?  build to an analogous pattern, but forget the metal altogether?

A Kang, yes

I just saw this thread and started to trawl through the posts looking for any reference to a Kang.

all the while  thinking 'They're trying to reinvent the wheel here'.

The Chinese had them around 400 BC.
A simmilar technology was used by the Romans to heat buildings, especially bath houses,
but was lost to Europe after the demise of the Roman Empire

Kang furnaces are still used in rural China today.
acording to one study 85% of homes in northern China over 65million of them in use.

Some points to consider in the design:-
-draw air from outside building for burning

-combustion/expansion  chamber should be about 3 times cross section area of the rest of horizontal flue for more efficient heat transfer.
there will be  contraction of gasses as the heat is pulled out of them as the travel through the horizontal flue.

-make  3 or 4 180degree turns in the Horizontal flue to scavenge maximum heat and allow for wide area rather than long.

-at the base of the vertical flue there could be a door to open in order to a build a small fire to start the flue drawing air just before the main burn is ignighted.

- the kang can be built as a raised section above  floor level or as a bed
...or it can be at the same level as the floor and the side loaded burn chamber accessed via a sunken section below floor level.
- a side loaded burn chamber may be easier to clean out than a top loading one.

- I'd definitely build it all with brick and the burn chamber with refractory bricks and cement if possible.

-if  metal was used the expansion and contraction would need to be taken into account , but it would also likely burn out pretty quick and just interfere with the function of it.

Thats how I'd start anyway.

I've been wanting to make a Kang for many (about 20) years but haven't had the opportunity or need... yet.

Hope this helps anyone wanting to make one.
post some pics if you do

speedy wrote:
A Kang, yes

I just saw this thread and started to trawl through the posts looking for any reference to a Kang.

all the while  thinking 'They're trying to reinvent the wheel here'.

It's not a reinvention but an improvement.  The concept is old but the implementation is different with the idea being to improve the efficiency, ie more usable heat from the same amount of wood.  The older implementations were leaky and lost large amounts of energy up the stack and as smoke.

I'm sure there were/are very efficient systems already.
Smoke is an obvious sign of inefficiency and easily addressed.
introduce more air for a complete burn.
this could be done by redesigning or increasing flue length for more drawing of air.

Choice of fuel can play a role here also.
bundles of small sticks would be better than logs as there is more air and they burn fast and clean.
the efficiency or the system is also in capturing heat quickly, storing it and giving it up slowly.

another advantage to using small sticks is that they take less time to grow.
ie. a shorter solar energy cycle- compare 1-2yrs for stick, 5-20 yrs for logs and many millions of years for coal ,oil or gas.

I wouldn't consider metal in the design as it will have too much movement over temp variations, except maybe in the vertical flue, and this will damage mortar joints or earth construction and cause it to leak.

metal transfers heat well and wont store it well.
it can also burn out , esp. with high temp fast burns.

masonary construction is key to storage of the heat.
The horizontal flue (heat sink) should be horizontal or slightly inclined.
any decline will interupt flow and efficiency.

If they're smokey, they're not being used properly or not designed properly IMO.
 

Well Speedy, I took a look at the Kang and the only thing i can see in common is that it uses fire to make heat and that heat is stored in a mass and the mass can be used to heat folks.

I don't think that anyone is claiming to invent fire and mass here. The Kang didn't have the heat riser like the rocket mass heater..

So is the Kang a rip off of a caveman's fire that heated a rock and the caveman slept by the rock?

maybe there are Kangs without a flue, I've not seen many to comment.
I've always envisaged them with a flue and to have one without it would be prevent it from even working.

When you talk of 'heat riser' you do mean a flue don't you?

No. The heat riser is an insulated vertical chamber where the hot rising expanding gases cause a high pressure area which in turn creates a low pressure area behind it. The effect is similar to a water pump as atmospheric pressure rushes to fill the vacuum created and this causes very efficient combustion..

Here is a vid by Paul showing Ernie and Erica demonstrating one.

http://www.youtube.com/watch?v=qtFvdMk3eLM

The RMH is more like a Russian Masonry Heater than the Kang...or maybe an ingenious use of both systems.

By the time the exhaust gases get to the part you call the flue most of the heat has been transferred to the mass.

Thanks Ronnie,
seeing the the vid seems to have cleared a few things up for me.

So, the way I see it now , and ho it differs from the kang is that it has the flue inside what is effectively an expansion chamber immediately after the fire box
The flue , being insulated becomes superheated above flashpoint of volatiles (which otherwise become smoke) and allow complete combustion.

The gasses have room to expand in the drum, radiate heat then contract as they cool.
The contraction adds to the flue effect but in reverse.

It sounds more  analogous to a Jet , or more specifically a Ramjet than a Rocket .

Like you said, similarities with Russian masonary heater and Kang combined , yet still different in its own way.

You've got it Speedy!

This was the earliest thread here where we talked about the contraption as a butt warmer. Some of the time we were stumbling around in the dark. There are other, more recent, threads here where we discuss the Rocket Mass Heater also. 

The RMH also  has similarities with Dr. Larry Winearski's stove that he made to help with cooking in third world countries. Someone at Dr. Winearski's camp named it rocket stove. So you may be right about the jet - ramjet, I don't know.

Ernie and Erica could explain things much better, but they get busy and it is a while before they get time to join in here.

If, you play the video that Paul has at the top of the page, (at this time) it shows the "rocket."

My impression is that Ianto Evans is the inventor and Ianto taught this stuff to Larry and then Larry later ... uh .... enhanced his personal story.  A lot. 

But, I wasn't there, so what the hell do I know.  Other than bringing it up is something that could brew up a bit of a storm right here.    Based on my limited knowledge, I tend to favor Ianto's word.  So when I see words to the contrary, I feel powerfully compelled to set the record straight.

Well Paul, I wondered about that, but had no other info other than the stories that i read about the rocket stove...

tel wrote:
anyhow, made me wonder: could you build the mass, including the flue, entirely out of bricks?  I don't know that there would be a good reason to, but would it work?

how about building the flue out of bricks, then covering that with cob?  bricks are likely to be more expensive than galvanized duct if you don't know of salvage opportunities, but I could see some advantages.

hell, could you build the whole thing out of brick?  build to an analogous pattern, but forget the metal altogether?

any opinions on this?

works a bit slow but OK.

I am not getting into the Ianto and Larry tiff thing. Aprovecho has the original work i suspect.  IMO its of no import at this time just bad blood.

both types do the job they where designed for and we are pushing the RMH into doing its task better than ever with as much of the same simple passive design as possible. my only gripe is that the principals are being diluted due to language similarities.

the stoves where named for the sound they make as they burn; they use principals from several traditional types of stove. since the only time they pulse like a ramjet would is at the extreme of a very long burn i dont think the ramjet stove would be a very good name.

Ok - I'm new to this so I'm probably asking a question that's been answered a thousand times.  I don't get all the monkeying around with bricks and scrap.  Wouldn't it be easier to just weld the whole thing together out of 1/4 inch pipe scraps?  A 6" pipe for the feed tube and combustion chamber and then an 8" pipe for the riser?  If you are welding it you would guarantee it is all gas tight.  Also, instead of a freeform cob thermal battery, could you just build a reinforced wood box and fill it with concrete?

Alaska, you could do all of that but you miss the point.  Not everyone has welding skills nor equipment.  The materials used are readily available and the tools/skill sets fairly universal.  The imbedded energy in concrete is immense thus local clay used to make cob is a better option.

Sure Alaska try it out and let us know how it works.

Ernie wrote:
nope the aluminum tape is the same stuff sold in hardware stores for sealing house ducting. made by 3M i think; sticky on one side.

if you wanted to just use sheet foil you could make flour paste glue and get pretty much the same effect.

Just my two kopeks here... After taking my Home Energy Rating System (HERS) class, I would NEVER EVER use any kind of tape when bonding two pieces of HVAC metal together.  The longest the tape will last is two years; then the adhesive dries out.  To seal metal ducting together you need to use mastic.

Will do.  I will try to take pictures and use bolt-together flange fittings where i can.  My goal will be to have something robust and gas tight with as little welding as possible.  It will also be somewhat portable that way.  It should also be easier to fabricate so if someone doesn't have welding skills they can have it made relatively cheaply by a welding shop.  Nice thing about oil pipe is that the flanges are all standard fittings and gas tight.

I'm sorry if I'm not respecting the politics of the rocket stove concept.  I'm frankly just trying to make something that keeps a place (an off grid sauna) warm at -60 without burning a forest of trees just to sauna every winter.  I already do that for the main cabin.

I have no idea what clay resourses i have around me (i'm about 50 miles off the road system).  I do have sand and gravel and can haul quickcrete in by the sackfull.

Muzik the duct is buried in cob it dont matter at all if the adhesive losses its sticky. all its for is to hold the duct together while you build the bench or bed or what have you. the tape will last way longer at any rate cause its basically shrink wrapped to the duct by the clay shrinking so either way you win with tape.

I just purchase the RMH book and first off I noticed the first page is blank compared to the dead tree version with the nice picture. Wondering if its just me?

With regards to RMH and passive solar design. I have a waffle slab planned to go in for the foundation as the soil is reactive clay and with the extremes in the weather it will dry out more than it did before eratic weather patterns.

Is the idea with insulated slabs still to only insulate the perimeter and leave the middle bit in contact with the ground? And where would be the best location for a RMH? I try to find one in the center or middle in the main living room but with the RMH and the horizontal ducting I have a problem. Any direct horizontal run will hit a traffic point where people will walk and cannot be blocked.

The only alternatives I can think of a are vertical venting outside the house outside the roof or placing the RMH against an outside wall such as the west facing wall and having a short bench and then venting outside.

With a direct build onto cement would you still go for an insulation layer? Will a constant thermocycling of a heated mass on the cement crack it?

Would love to build cob or alternative structure but the local government has made it too tough so I'm going with a slab on ground passive solar design home as the next best thing. The only problem I have not solved is winter heating and RMH looks the ticket except for the local government again. Has any of the approval applications been progressed so far pushing them as a masonry heater?

I have looked into masonry heaters but not liking the huge cost to get one installed so I got the RMH book as an alternative to consider.

Just hope with the govt im not going to end up having to build a RMH in a shed out back and live in that in winter just to make it through the low 20's F winters.

Cheers,
PeterD

David House wrote:
up at the top of the doubled pipe, the exhaust is as cool as it will get while we still have it in our grasp. At the same time, the incoming air is also as cool as it will be, meaning that the temperature difference between the two is as much as we can reasonably expect. Likewise, in the middle of the pipe, the incoming air has heated somewhat, but the exhaust is also hotter. And down at the bottom, whereas the incoming air has been heated still more, the exhaust is likewise as hot as it will ever be. So at all points along the pipe, the temperature difference is as great as it can be between the two gases.

... the ultimate effect, once more, is that heat is retained in the shelter, and no cold air is pulled in to the shelter to feed the fire. The efficiency of the whole system then-- which will translate into how much wood you have to chop, carry and feed the stove-- is getting better and better. The stove, then will use less wood to produce the same heat, or will produce more heat with the same wood.

David,

What you are saying makes perfect sense to me.

I am much appreciative of you sharing the concept with the rest of us, and would like to utilize the principle when building a rocket mass heater. 

We have fresh air in the house, that we breathe, that would be sucked out of the house by the fire, just like with any fire, and we hope there would be enough cracks, to let more air in to replace the demand by the fire.  The more raging the fire, the less air left to breathe, as it would soon be totally consumed by the fire.  I would rather the fire have a feed from outside, especially as you have described, and that it not be competing for the air that I breathe.  The warming effect on the intake air is a plus.

speedy wrote:
Kang furnaces are still used in rural China today.
acording to one study 85% of homes in northern China over 65million of them in use.

I'd definitely build it all with brick and the burn chamber with refractory bricks and cement if possible.

speedy wrote:
I wouldn't consider metal in the design as it will have too much movement over temp variations, except maybe in the vertical flue, and this will damage mortar joints or earth construction and cause it to leak.

metal transfers heat well and wont store it well.
it can also burn out , esp. with high temp fast burns.

masonry construction is key to storage of the heat.

Masonry heaters have historically been constructed from masonry, so masonry should work as well for rocket mass heaters.  Metal does not store heat well, and does transfer it well, i.e. right out of the structure.  As you have alluded, that is probably a reason why metal stovepipe is used for getting a good draw out of chimneys.  Also, metal stovepipe is quite expensive.  I would rather put that expense into masonry. 

I would like to see more discussion of using masonry for the horizontal tubes, in particular for the heat storing sections of the heater. 
For comparision, below is an image of a masonry fireplace, that does not contain any stovepipe.



http://www.grannysstore.com/Do-It-Yourself/masonry_stoves.htm
http://www.daviddarling.info/encyclopedia/M/AE_masonry_stove.html

might do for you to read the book and see where and why we use a drum for that part of the stove. as well why we use DUCTING in the bench. it has little or nothing to do with draw cause we dont need draw except in a very specific place. if folks wish to discuss masonry heaters please feel free to start your own thread. its a waste of time to try and answer questions on RMH systems only to discover someone has decided that they not only dont have to know anything of the subject being discussed but there personal favorite method is appropriate dispite the subject of the thread.

So I'm trying to get my wife to let me build a version of this where our double sided open fireplace is, one thing she really like about the fireplace is being able to see the flame from her couch. is it possible to put some glass somewhere that the flame could be viewed without damaging the effectiveness too much?

FYI I will be building mine out of bricks as there's no way for me to talk her into cob lol

Thanks all

you can use a wood stove as the fire box. I dont know how your gonna get the height for the barrel into a fire place. the whole structure can be made of brick if you make sure its short enough to mitigate the slowing action of the brick surfaces on the exhaust. its simply a design problem. getting the radiant heat balanced for the barrel is more the concern. you might try thinner bricks or tiles for the barrel/re-burn area. I cant speak directly to this since i have not built that specific part out of brick.

tel jetson wrote:
anyone ever heard of a kang?  seems somebody beat eco-weirdos to the mass bench idea by around two thousand years.  maybe the kang connection is already widely-known in this crowd, but it was news to me when I stumbled across it today.

anyhow, made me wonder: could you build the mass, including the flue, entirely out of bricks?  I don't know that there would be a good reason to, but would it work?

how about building the flue out of bricks, then covering that with cob?  bricks are likely to be more expensive than galvanized duct if you don't know of salvage opportunities, but I could see some advantages.

hell, could you build the whole thing out of brick?  build to an analogous pattern, but forget the metal altogether?

It is known as lots of other names too, but I don't think the RMH people claim the bench as their own idea. The masonry heaters have used the same thing all out of brick for a long time too... right down to the benches and in fact there is someone working out a masonry heater with a rocket style burner (perhaps "rocket principle" would be a better way of saying it). However, masonry heaters cost a lot.... as much as some cob builders have spent on their whole house or more. They also need a very good foundation... a RMH does too, but not to the same degree. The whole idea of the RMH is to be in reach of the very poor in 3rd world countries (where we are headed).Able to be made by the home owner with little in the way of skills or training.

Both a masonry heater and a RMH try to do the same thing, Burn the wood fast and completely by insulating the burn chamber and store the heat to be released slowly by heating a large pile of mass like brick or cob. The masonry heater does a large short burn with all the fuel loaded at once and then heats for a long time. The RMH is similar, but generally the fuel is fed by smaller amounts at a time. They both have their place. The masonry heater is easier to get a permit for because it looks like a fireplace and uses materials and formulas the building department is used to.

I think both are much better and cheaper (and safer) in the long run than the cast iron box.