Questions on Rocket Mass Heaters

Hello everybody,

I have a few questions regarding the building of my first RMH.

1. I bought a 55-gallon barrel from a local gas station. For some reason I've been led to believe that some barrels are thicker than others..is this true? And if so, how do i know that my barrel is of the thicker kind? I want to be able to go for at least 7 or 8 years without having to replace the barrel.

2. Where I live steel piping is very expensive and buying it used is impossible. Can I make the bench piping out of cob or some other super-cheap material that will last for many years?

3. If im using refractory bricks for the heat riser, do I need additional insulation between that and the barrel, or are the bricks enough?

4. Does clay and sawdust really work as insulation? I can't shake off the feeling that sawdust will incinerate if I mix it with clay as insulation for the heat riser..

5. When I do the mock-up outside, the sides of the barrel get so hot that touching them hurts and i know that there's a gap of more than 1.5 inches between the heat riser and the barrel...so how important is it really that i maintain that distance of 1.5 inches between the two as outlined in Ianto Evans' book?

I appreciate any insight one may have for me..

Best,
Karl

Karl Meisenbach : O.K., Where are you located ! I am making a bet with myself that down below in the similar threads there is a link to possible sources of Used pipe !

Please consider going to rocketstoves.com to pick up your PDF copy $15.oo U.S.D., Of Evans' and Jackson's Great book 'Rocket Mass Heaters', there is STILL
no other book of information on the 'Rocket Stove Family' in any language ! ( And I don't make a Dime ! )

All 55 gal drums should last at least 10 years, This should not be a worry !

I would not recommend trying to make a Cob only - Rocket Mass Heater R.M.H., as a first build, you would need to fire the cob into adobe like flue pieces, then use them
to make up your horizontal runs inside your Thermal Mass ! Leveling/mating each and every piece would drive ME Crazy ! How much experience with Cob/Adobe have youh
had !

In a word, YES ! You want the most efficient R.M.H. you can build ! This is a simple and positive step that should add almost no time to the build itself and wiil always
produce positive results !

Clay slip and sawdust will make a superior insulation material, the sawdust turns to charcoal and you end up with a ''Clay-Foam'' material that is very light and insulative!
It IS very friable, and will not take being knocked about, but placed in areas where it will not be Physically assaulted it is very useful !

Karl Meisenbach : Go to the list of 'Working with this site' tools in the upper right of your screen between the Pemies Banner and the Permies 'video of the day'. Click on
the search tool and then find the Google search tool and type in 'Finding used stove pipe' and use google to search in Permies - This will connect you to several Forum
Threads where this topic has been discussed ! Good Luck ! AL.

Allen,

Thank you for your reply! As you mentioned, clay slip and sawdust make a great insulation material? I want to put it between the heat riser and a steel pipe, which would all fit within the 55-gallon drum, thus creating the 1.5 inch air space all around as mentioned in Ianto´s book. Is that a good use of it or will it fry?

Also..newbie question..what is clay slip? Haha..youre probably thinking "uh-oh..why didnt i take the blue pill with this one.."

Finally, I live in Uruguay..steel piping is not cheap, and used piping is nearly impossible to come by.

I have Ianto Evans´s book, but i feel like there are gaps which will only be filled with my experimentation.

Thanks,
Karl

I am in Argentina, and steel is also not cheap, i wanted to make the heatriser with refractory bricks but ended up buying a used 8" cast iron pipe 8mm thick, so far so good after 2 months, maybe it lasts 2 winters, but i also tried to make the insulation with a castable mix so when the pipe burns away it all doesn't fall apart.

So the castable insulation is another option when not using bricks for the heatriser.
there are different ways to do it, someone uses clay, cat litter, paper and perlite i think.
as for sawdust, i wish i heard that before, i would have used that too!

Karl Meisenbach : Help is coming, Hold on to the last! This is where the fun starts !

Clay slip, first you find some local clay, Then you google clay sedimentation test ,or just sediment test to see how good your clay is, and if you will have to clean it !
Some silt in your clay is not a failure ! With nearly pure clay you make up a slurry that will when freshly stirred, just barely hold the shape of a finger dipped into it
for a couple of seconds ! There is of course, dry bagged clay, and it will work also but clay is truly universal, it can always be found if you look for it !

When you are fitting together your bricks outside for your first build out of doors you want to briefly dip your bricks in water and then use your clay slip LIKE a
mortar to lay up your brick. This will seal the small air gaps that create problems at this point !

With an 8'' system, you will need pieces of 8'' stove pipe as an inner wall, and a second metal skin for the Outside of the Heat Riser, regardless of the type of insulation
you use. For a 1st build, perlite and just enough clay slip mixed together will make an excellent Heat Riser! This is the very thick stuffing In a hollow jelly roll with an
inner and outer metal skin ! Here the inside piece(s) of the 8'' pipe is a sacrificial form, we know it will fail Within 2 - 4 heating seasons depending on how much your
R.M.H. is used, the clay slip and perlite formed Heat Riser Core should last at least a couple of years past the initial failure of your metal stove pipe inner wall ! Clay
Slip and Sawdust will do as good a job as an insulative formed Heat Riser up until the time that the metal skin of the inner Wall fails ! When I called the Fired clay and
Sawdust mixture a clay foam perhaps I should have compared it to sea foam ! It will serve very well for an insulative layer under the bricks forming the bottom of the
Burn Tunnel !

Perhaps you can find a dead water heater,whose outside metal skin can be cut down to overlap itself and make the outer wall of your Heat Riser, allowing the !.5'' side
-wall to barrel gap ! This is a start and should help !

For the Future Good of the Craft ! Be safe, keep warm ! As always, your questions and comments are Solicited And Welcome ! PYRO - LOGICAL Big AL !

P.S. Karl, I re-read everything and see that you have done a practice burn out doors ! The next step is to burn out/off the paint on your barrel, Look at the 'pocket rocket'
pages in your R.M.H. book and get creative ! Do not skip this step, your lungs will Thank You !

Own Sawdust!, if I new I would have used too. I think you should insulate firebricks too as some fire bricks are only resistant to hit but don't provide great insulation.

Allen, Let me quote you as I have a tiny question: "Here the inside piece(s) of the 8'' pipe is a sacrificial form, we know it will fail Within 2 - 4 heating seasons depending on ow much your
R.M.H. is used,"
you mean making the inner tube of the heating riser out of a regular galvinized 1mm 8" tube?

cheers.

Carlos from Uruguay too.

Et al : Because this is totally a sacrificial form, to hold the true components of the Heat Riser (usually Clay slip and Perlite) We don't really care what it is made of as long
as its' outside diameter is nearly or just larger than 8'' True ! I would be a little nervous of using sections of Aluminum stove pipe at this location, but just about anything
else would work ! Here in North America there is a type of thin wall cold air return ductwork that is made up of lightweight 'Blued' steel. It is subject to rust,and most Fossil
Fuel Fired Furnace installers will Not use it in installations, no matter how cheap it is! There are literally Tens of Thousands of feet of this lightweight stove pipe setting in
hundreds of warehouses and hardware stores waiting for an end user to show up and make an offer on them ! As I am expecting that any pipe used as the metal skin of
the inner wall of my R.M.H. will Quickly fail, and because I believe that within the next 4 -5 years there will be much better and cheaper Heat Risers for sale then the best
Heat Riser I can make today, I do not find any problem with this planned obsolescence on my part !

There is nothing to say that a heat riser could not be made up as a separate independently fired piece, created even before the Rocket Mass Heater was originally field
tested out-of-doors, Cardboard Sonotubes, or others could even be used for this purpose ( I Think ! ) Hope this answers your Question !

For the future / good of the Craft ! Be safe, keep warm ! As always, your comments and questions are Solicited and are Welcome ! PYRO - LOGICALLY Big AL !

Hi Allen,

Thanks again for the info! As im using refractory bricks as the heat riser, im assuming the 8" sacrifical metal pipe does not apply to me. And as for the piping that goes around the heat riser and encases the insulation, im considering just using wire mesh. Its the only material thats within my budget and if it fails, then ill at least have the remaining perlite/clay slip form.

Is my logic sound so far?

Other than that, I have a list of problems that would otherwise be easy to solve if I had Home Depot nearby..so I wont even begin..

Yeah, I'd love to have a home depot down here and the zillions of precious things people on the first world throw away up there but we don't have that and we have to improvise to have those beauty inventions up and running.

and BTW winter gave us a break and temperatures were in the mid 20's Celcius this week so no burning and no fun. My bench is almost dry and I am planning to sleep on it next week.

best wishes,

carlos from uruguay

Yes, winter has been gentle on us this year..

As for sleeping on the bench, that would be the highlight of 2013 for me if and when I get to that stage!!

Karl M.: Love your logic, and don't worry about thinking outside the box, If your thinking was too straight, you never would have started this project.

If you are thinking of using perlite and clay slip as an additional layer of insulation next to the interior wall of the barrel I can be very generous with your materials
- go ahead and give it a try! I would want to used the smallest mesh that I could get, make sure that every single piece of perlite was darkened with a coating of
clay slip, you will have to make it extra dry to make it extra stiff ! you can't allow any slumping of the material making up your Heat riser. as you will have to maintain
that 1.5'' gap everywhere inside the barrel !

Or you could avoid this potential problem area by just using Rock wool Held in place with Small mesh wire !

For the Future/Good of the Craft ! Be safe, keep warm ! As always,your questions and comments are solicited and Welcome ! Pyro-Maniac Big AL

Three questions about rock wool as heat riser insulation:

1. Is it toxic?

2. Will it eventually incinerate?

3. And will the wire mesh holding it in place eventually fail due to heat exposure in turn causing the rock wool to fall out of place?


Also, I may be missing something but im using refractory bricks as my heat riser..

Karl M. : Basically its spun glass ! It might sinter a little or melt/fuse but that will help hold it in place after the mesh fails !

Go to the sister site to permies.com , which is - richsoil.com - and click on Rocket stoves, while slightly dated these videos are all done by professionals or by
direction of professionals, you will learn a bunch of stuff you are ready to learn !