Rocket mass heater 30 gallon barrel?

Building a rocket mass heater in my shop for this coming Adirondack winter. I am using 6" pipe and flues and was wondering if anyone has an idea that a 30 gallon barrel would work ok for this. I have built 3 different prototypes outside and fired them up using no mass but just a straight 6" stove pipe connecting at the bottom of the barrel. I have the burn tube (6" metalbestos 3 feet long) 2 inches from the top of the inside of the barrel.
The latest version seems to work well, the only thing is that the coals seem to build up in the horizontal part of the fire chamber and slow the draft. Maybe just putting too much wood in, plus the prototype does not have the draft that the finished one will have. I plan to run the flue pipes between cement blocks and cover them with sand- maybe a total of 20 feet. Need to be able to dismantle it in the spring because of limited space. Looking for any comments/suggestions. Thanks. Jeff

Jeff Rutkowski : Welcome to Permies.com and to the Rocket and Wood stoves Forum/Threads from a fellow 'Up-State'r' , The magic of the Rocket Mass Heater R.M.H. takes place
as the hot exhaust gases leave the top of the barrel, cooling and falling to the transitional area at the bottom of your barrel. The heat radiation that occurs here is what creates the
Thermal Differential Engine Effect that 'powers' the R.M.H. to 'drive' the hot exhaust gasses horizontally through the Thermal Mass. Given Two different sized barrels on two identical
R.M.H.s they both have to radiate off just as much heat energy to make that Heat Engine Work !

Counter-intuitively, the smaller barrel will radiate its heat off at a higher temperature than the larger barrel. Less surface to mass, or skin area to weight, and it must do so at that
higher temp ! This is the reason when your 3 year old wants to be 'picked up' they are such a great snuggle, their lower skin to weight ratio, requires them to radiate at a noticeably
higher temperature !

In your last sentence of the 1st paragraph you printed Burn Tube, which I took to mean you were actually talking about the Heat Riser ending 2'' from the bottom of the barrel. You
should consider going to rocketstoves.com for a PDF Copy $15.00 of Evans' and Jacksons great Book "Rocket Mass Heaters'', there is STILL No other book in
any language that contains as much 'Rocket family' information ! (And I don't make a dime !) This will allow you to use the same words to mean the same thing while getting help
on these pages ! It will also save you lots of time in Not coming to Permies with All of your questions. However, the only dumb question is the one that didn't get asked !

I am assuming that we are both talking about a J-Tube style of R.M.H. With the feed tube located on top of the R.M.H. just below the Barrel and that you are loading the sticks
vertically. The idea is to use extremely dry, finely split wood to start and feed your fire, which should self maintain, burning only the lowest end of the sticks, and perpetually
gravity feeding itself more wood as the ends burn, This is really the only finicky part of operating the Rocket, It is possible to over feed the rocket and feed bigger wood to soon,
this will cause that pile of coals and ash that you are getting !

Depending on the amount of insulation surrounding the bricks in your Burn Tunnel/Combustion Chamber, and again on very dry wood you are slowly building heat within that area
until it is glowing red hot, at that point your next piece of wood will seem to Spontaneously Burst into flames as it is added through the Feed Tube! At this point you can burn 3 - 6
sticks of wood as large as the feed tube will take. Again this is an indefinite amount of time, depending on insulation and the types of material the Combustion chamber is made from
and very dry wood, Most first build R.M.H.s take between 45 min to 1.5 hours to optimize temperature when cold, depending on the initial skills of the Owner/Builder !

And now I most be unkind, There are Three major flaws in using Cement blocks anywhere the internal temperatures reach 400F (and paper Famously starts to ignite at 451F ) the
lime in the concrete starts to fail, the rough surfaces will create turbulence exactly where you want smooth flow of your hot exhaust gases, and you will find it almost impossible to
seal cement block Edge to Edge, without leaks. Due to the rather porous nature of cement blocks( we seal outside basement walls with tar and membrane) it is not proof against
leakage of gases.It is also quite insulative as is your sand ! The perfect answer for this is horizontal stove pipe and Cob ! Wet cob covered in wet hay/straw,sawdust and covered in
plastic will Soften and slump, within several days and can be cleaned up after, Hard Cob with a center core of structural clay can stop a small farm-type tractor !

I personally know that many people have proposed and/or tried to make Cement Block work after the hot exhaust gases have past the first 6 feet of the Thermal Mass, I know of No
single use of cement/concrete/cinder blocks that has been reported to work, Y.M.M.V. I hope this helps, and is timely. For the Good of the Crafts and Permies!

Think like fire, flow like a Gas, Don't be the Marshmallow ! As always, your comments, and questions are solicited and are Welcome ! Pyro - Magically BIG AL !

Thanks for the timely and helpful info! You are correct about the design- J-tube, heat riser ending 2" from the top of the barrel, and loading sticks vertically. I especially appreciate your volume to surface area discussion, after spending 10 winters in Alaska- although a few of those were in the Tongass where it is much warmer than the ADKS in the winter. I was not too clear on what I'm doing with the blocks. I am going to run the 6" pipe along the floor between two rows of block and fill the spaces up with sand, elbow up at the end of the run and run a "second layer" of pipe, block, and sand back toward the barrel and then put the chimney up just before I get back to the barrel. I may not use the sand but use cob instead as you have suggested. That sand has got to have a lot of air in it.
Time is of the essence now that I am in the middle of cider season, putting a new sugarhouse in, bottling honey, tending to about 300 raspberry bushes, and slowly getting the firewood into the shed. You know the drill, being an upstater yourself. I would like to be able to get it all apart in the spring- the cob I could re-use next season if I have time to make it this year. I think I will get that PDF you spoke of. The idea being to have enough time for one more sailboat outing and one more cruise on the 33 year old motorcycle up through the park and back- I am in the southern part. Thanks again.....J

Jeff : Just yesterday my wife Martha and I stopped into our C.S.A. as they started to create a cider workshop, ( An Intentional Community which shall remain nameless ) They
had re-purposed an old, small, home garden, wood chipper, Troy-built or smaller and by quartering this years bumper crop of apples literally ground the apples perfect for cider
pressing with three steams, a foamy rich pectin over flow from a course chopped pulp,and running out of both, a fine sweet beautiful example of the nectar of the gods, with an
early promise of The Drink that gratified the American Pioneers ! I will be posting pictures to a new thread within a day or two ! For the Good of the Crafts Big AL !

Late, Note : Up here we call those great big encrustations of snow,ice and salt that hang off of high milage vehicles Feumits, meaning animal spore, The ones you hit near railroad
Tracks and pot holes and come off of 18 wheelers can break cars ! I was thinking about parking cars indoors and the tons of slush that usually came off of them, probably not good
for cob - also not much time to gather clay, the blue stuffs crap, see your local potter who mixes grades into a common barrel and will give you a deal or buy fire clay 60, again
ask your potter ! A.L.

Jeff Rutkowski : O.K. More counter-intuitive stuff, but you did O.K.! As soon as you have dried your clay, you soak it in water! Stiff but wet clay with some water in it really takes
a long time to suck up enough water to be pliable, sometimes you will hear people say 'plastic' but that actually means how much handling it can stand and is slightly different !

In a perfect world your excavator would have cleanly removed All the over burden, leaving you just clean clay to shovel into buckets, with no topsoil mixed in! You want to put
the clay you just dried in a cleanish bucket and rehydrate it, in about 48 hrs you can trust you hands in there and break up all the chunks with fingers, let it set till the water is
mostly clear, and keep pouring it of ,save about a gallon of slop off of the top to make clay slip and go back to pouring off clear water off of the top !

I actually had to go to U-Tube land to get two videos that show how to deal with hard clay ! They seem decent and were made by a man with hundreds of videos on his craft, the
lack of responses to questions, bothers me a little, but if you had all his videos you could spend all day answering the same question for 10 different people everyday- any way
the videos seem alright if a little log ! go to you tube and enter -

- ' youtube.com/Watch?v=c2hFwMt2v34
- ' youtube.com/Watch?v=SmoL8a-uSYM ' - alittle long, but with the view , other wise go for fire clay 60 or mortar-(ING) clay

For th' Craft, think like fire, flow like Gas, Don't be the Marshmallow! As always, Your questions, and comments are solicited and are Welcome ! PYRO - Logically BIG AL !

Rats. I tried the links but they are both for organ donors in Norway.

Jeff ; I am sorry lets try to work around my short comings ! Go to you tube and type in Simon Leach pottery, if that does not work got to simon leach channel,
or failing at that you can try - ' Youtube.com/user/sleachpots ' - You want the video that talks - ' Slaking Dried Clay " - about and you should also take a look at
' How to soften up clay that's too hard to Throw! " With about 300 videos you will find it if you look ! Big AL !

HELLO. Yes, I have not checked in for a while.  My rocket mass heater was wildly successful.   you can check it out here :

https://youtu.be/YYAJu-WyT24

I had to take the rocket mass heater apart and remove it from my workshop because I could not afford the space which it was occupying.  I am in the process of having a Froling S3 turbo wood gasification boiler installed  with an integrated solar hot water system and approximately 1100 gallons of thermal storage.