My first RMH! Lot's of questions need answering

I am currently planning a build for this spring/summer of a TMH. After the polar vortex we are done with waking up every 2 hours to add wood to the wood burning stove and still wake up in the morning with frozen pipes. I have read the book and done some research but I figured asking the questions directly would make things simpler.

My plan is to get an 8” Dragon Burner core to save a lot of the guess work on getting it all setup just right. Also the wife has demanded that this look nice so using a metal barrel is out of the question since from what I read covering it with cob would lower some of the efficiency (please correct me if I am wrong on this). So my idea is to build it out of firebrick instead as my understanding is that firebrick absorbs heat fairly quickly so it should still keep enough of a difference in temperature to keep things running smoothly. Would this work?

My next question is to the location of the “barrel”. I’ve been seeing them placed off center of the heat riser and I read that you want to keep the temp lower on one side and higher on the other but I’m not sure why or what this actually does.

With the spacing between the “barrel” and the heat riser according to the book it should be 2-3” for an 8” system but more would be fine. What is the advantage/disadvantage of adding the extra headspace? Also my understanding is that you want the CSA of the heat riser to be the same as the CSA of the inside wall of the “barrel” to the outer wall of the heat riser (insulation) is this correct?

I am planning on building this system in my living room and I want to retain as much of the heat as possible, would a perlite/clay slip mix along the exterior wall and the floor the full length of the bench help with keeping the heat inside my house?

As for the bench itself, the book mentions using rock or some other material that can quickly absorb the heat from the exhaust tunnel then using cob the rest of the way but I have also read that you should use uniform material throughout the bench for best results. Which is it?

I am also planning on running the bench approximately 35-40’ but I have room to run it longer if I should. I have heard however that a 90° bend if the same as running the system 5 extra feet. Is this true and if so would a wide turn improve this instead of a sharper bend? Also, could I run it longer than that, besides the fact that it really won’t be providing much heat anymore is there any other negative?

Finally (for now) I have read that you need a vertical exhaust at the end of the system. If I run long enough of an exhaust tunnel that the temp is very low would I be able to just have a vent that goes out through my house similar to a clothes dryer or do I NEED the vertical exhaust? If I do need it can I use the chimney I currently have for my wood burning stove?

Mark Kansburg : Welcome To Permies.com, our sister Site richsoil.com ( check out the RMH videos there ) and a big Welcome to the Rocket and
Wood stoves Forum/Threads ! With over 21,000 fellow members world wide you can come here 24 / 7 and should find someone who wants to talk about what
you want to talk about. I came here to talk about Rocket Mass Heaters and now am helping people on many forums every day ! Enjoy !

"The Book " is your #1 source of information, any questions you have you can come here for help, and count on 1 or more good answers to your questions.
I expect the good ladies at Dragon Heaters will contact you through these pages, they are very knowledgeable and helpful, you can go from there.

The generally spoken quotation for Heat Energy provided to the living space is 40% off of an uncovered Barrel, and 60% delivered to the Cob Thermal Mass,
many people have had good luck skim coating the barrel, and find that the prompt heat that is not radiated off of the Barrel is simply delivered to ether the Cob
Thermal mass or 'the Bell'

If you are talking about Replacing the Barrel with fire brick I would have rather grave doubts about how well that would work for you especially on a first build,
While the metal skin of the Barrel is able to quickly absorb and re-radiate the heat off of it's surface, the Insulative qualities of the brick slow down the heat
transference, without which we do not have the 'heat engine' that drives our hot exhaust gases 40' horizontally thru our thermal mass!

Please find the list of the previous Rocket Stove Forum Threads, And click on the Thread "Fake Fire Brick'', then scroll down to, and read Erica Wisners entire
Tread Extension of Dec 20th, there she corrects a few errors that I posted in that thread! While long it is worth the read, and ill further explain why fire/kiln
brick is not god for the barrel exterior !

Today Dale Hodgins posted a clear description of the difference between The Specific Heat a material can hold and heat transference thru that material,
Its Thermal Conductivity. this will also introduce you to the Engineers Toolbox


Using Splits or 1/2 thickness fire/kiln bricks to make an exterior wall/shell, while definitely improving your heat transference, will certainly make for a much
more challenging build, into the class of work done by master masons skilled at building (pricey) masonry heaters !

Most people do not place their barrels of center or eccentric to the heat riser! Generally it has been noted that the side with a narrow or pinched Constant cross
sectional area flows less hot exhaust gases, and runs cooler, This will help you in attempting to locate your Rocket Mass Heater RMH, closer to possible
exposures you might want to protect while shifting the RMH to make more room for a pass-through or walk way.

Moving the barrel off-center has also been found to promote the smooth and swift flow of hot exhaust ages through the Manifold section where the Exhaust
gases failing vertically, are channeled to then flow horizontally into your Cob Thermal Mass. The manifold is one area while the Cross sectional area should be 2
or 3 Xs the other cross sectional areas, this is an important part that the book is weak on, but nearly everyone agrees that here bigger is better !

A final thought before we move on, a tall Heat Riser, more than 3 Xs longer than the Feed tube makes for a Rocket burner that performs very well creating a
strong draft. Occasionally, people have reported a reversal of the hot side and cool side of the offset barrel with the Extended Heat Riser, I Don't Know Why !

Headspace between the Heat Risers Rounded and Sculpted Top and the underside of the barrel is a bit of a trade off, minimum for a 6'' system is usually quoted
at 1.5'' and the minimum for the 8'' system is usually quoted at 2'', This creates a very hot barrel top and is often used as a second cooking, slow cooking and
warming area. Ovens constructed out of nothing more than multiple layers of crumpled Aluminum foil shiny side in have baked bread handily !

Again, the common use of a extra tall Heat Riser, more draft, allows us to easily expand that head space, it also raises the height of a final 'barrel' to heights
un-handy for using the top for any thing but a place to stack additional bricks or a large kettle of water for winter humidification !

You have not made any reference to your location, or the way your home is built, Beyond cautioning you that your RMH will work best for you if placed in the
very center of your home, and that any attempt to place it in an out of the way location will result in feeding your RMH becoming an unwanted chore, and your
Dragon serving you as poorly as you serve it- You have an existing wood stove, so you have an idea what I mean, plan your build to always be within earshot
of your RMHs roar. You want to plan your build to protect your exposures leaving a dead air space between your Cob bench and any walls, especially outside
walls, other than that the answer would be yes !

If the Cob Thermal bench is uniformly built with the horizontally placed ducting at a uniform depth, and well protected with 2+ inches of Cob, than all the rest
of the space within the Bench can be filed with as much 'other' dense materials as you can find, again Cob First, then the dense fill in materials, go back and
re-read that section again, I think you will get a different meaning now !

Yes on the Elbows, the best are the Smooth 3-4 piece adjustable ones, the flexible material made for vertical use in relining chimneys, is very poor.

PLAN Your build around the Idea that you will have to have a vertical chimney !

When Ianto Evans First created the Rocket Mass Heater, He was able to find a place on the west coast with a stable micro-climate with very steady wind currents
during a curtailed heating season. Next He set out it custom build houses to sit low, down into the land like mushrooms all smooth flowing corners and (originally)
nothing over 15' high! With these criteria met, it was easy to design an exhaust that exited at ground level on the leeward site of his house ! This system worked
for him !

I am not picking on you when I say that most people could not tell you in what direction the wind is blowing past their house right now ! A storm of the decade can
come out of a different direction, and make a horizontally discharging RMH unusable !

An Airport 5 miles away could tell you all about its prevailing winds since it was created - AND have little use as a reference for Your location !

Your Existing chimney should be inspected by a chimney sweep prior to anyone trying to use it, also remember that Some Day someone else may assume that
a wood stove is a wood stove, and if a RMH will work at that spot their old ''Blast of Heat 5000'' will look rely good right there !

Come Back here often, if there is a RMH in your future we ill help you find it ! I hope this was timely, and helps For the Good of the Crafts.

Think like fire! Flow like a Gas ! Don't Be the Marshmallow, as always,comments/questions are solicited and welcome PYRO - Logically Big AL !

Thanks for the help Al. Just some more background. I am located in Northern New Jersey and I live in a Ranch style house that I have turned into an open concept house to help spead the heat of the wood burning stove. Th RMH would go in my living room where we already spend most of our time so it would never be left unattended while running. I'm attaching a rough design on what I would like it to look like. The outer boarder is a basic idea of how the living room is shaped and I the ducting ends at my chimeny. As for the chimeny itself, it is in good running order and I have in cleaned and inspected yearly since I heat my house totally off of the wood burning stove. I will go through all the information that you have pointed me in to try to get better informed on the RMH. I'm not building anything until the end of May at the earliest so that leaves me quite a bit of time to fine tune my plans.

For an 8" Dragon Burner, you need 8" stove pipe. I don't think you mentioned what size yours was. A lot of wood burning stoves only use 6".

Also, all the flue through the bench will need to be at least 8", as well.

On the other hand, I recommend that you take a look at our 8" castle build (including the write-ups on the blog about it). We use cut up chimney flue liners in a bell arrangement which is 24" x 30". This forms a structure to which you can adhere fire clay brick splits on the inside. In this way, you don't have to be a mason to use the brick. You can see on the website that we have incorporated an oven in another bell of the system. Bells actually absorb more of the heat in the exhaust than a long flue because temperature stratification takes place better. The bench arrangement shown in the picture is optional. And, the whole structure can be covered with cob, plaster, or stacked stone (we have a picture of this on the 6" castle build).

Mark Kansburg : Sounds like you have a good plan, please Do NOT take any video that you see From U-Tube at Face Value, there is a tremendous amount of crap
out there ! For the Good of the Craft ! BIG AL !

My chimeny should be an 8" at least that's what I measured at the cleanout in the bottom but I'll be remeasuring everything before I start building anything.

As for the spacing, it's obvious that to keep it away from the wall I just stop the cob short of the wall but how do you acheive that 4" gap between it and the floor?

If I used 24" x 24" clay flue liners with nothing else as my bell would it be able to handle the heat or would it crack over time?

Also, if I am limited to a 6" system would it be capable of keeping my 1300 sqft open floor plan house warm (mid 70°F's) as it's only source of heat in the winter?

Finally (for now) with my design as shown in the picture, where should I put my cleanouts?

If I used 24" x 24" clay flue liners with nothing else as my bell would it be able to handle the heat or would it crack over time?

Yes, the flue liners would crack (the first time you used it) because of thermal shock. Consequently, that is not what we recommend. Line it with dense fire clay brick adhered to the sides all the way up and down. The fire clay bricks store more heat in less weight than cob.

Also, if I am limited to a 6" system would it be capable of keeping my 1300 sqft open floor plan house warm (mid 70°F's) as it's only source of heat in the winter?

I don't think you live in Texas, so I would not recommend a 6" system in that size house. Better to get your chimney adjusted.

Just a few more questions.

From what I read it is recommended to keep an air space between the mass and any walls or floor. For the walls this is simply done by just not building right up to the walls. But how do I achieve this for the floor?

I am still a little unclear on the clean outs. I know I need one right at the start of the horizontal run but where else should I put them and what's the best way to make them?

I was also wondering about the manifold (barrel to ducting). I am a very visual learner and I have read about this area and how it should look but I am still a little unclear. If anyone could either provide me with a diagram, picture, or just a better discription on this area that would be a great help.

Mark kansburg : First, there is a LOT of Crap on You Tube, especially with the '' Flaming units of Death '' that get called Rocket Stoves ! Always take everything
you see on there with a long-ton of salt. Only watch what is recommended by someone you trust !

Having said that Goto=> villagevideo.org and find and clickon=> the You-Tube Icon, at the new page you will see rank and file of short videos the top row is labeled
Rocket Mass Heater Scenes, directly to the right of that description is a flashing ''PLAY " button Which will load that series of short videos in the correct
order to watch them !

This is ~ 3/8s ~ of a complete Video of a high end Rocket Mass Heater build, you will see how a Rocket Mass Heater can be turned into a fine Hand-crafted piece of
furniture, and find the answers to questions you didn't even know you needed to ask !

The combined sections plus more than that much again, are part of a DVD for purchase through Village video villagevideo.org or though the builders, Ernie and
Erica Wisner who are moderators on the Rocket and Wood Stove forums AT ernieanderica.info ! And yes they are friends of mine !( as much as an old crab has-
friends )

Minimum use of "T"s and caps for clean outs is every time you would use two elbows to change direction 180 degrees ! Following your sketch, one at the barrel, one at
the 1st 2' pice one flush with the top of the bench at the start of the 6' and your final clean out, outside !

For the Good of the Craft! Think like fire, Flow like a Gas, Don't be the Marshmallow! As always Your questions and comments are solicited and Welcome ! Big AL

We just wrote a blog about spacing between the rocket heater and the floor. This is important information, especially for 8" burn tunnel. The blog is called: Installing Rocket Heaters Safely and here is the link:

http://blog.dragonheaters.com/installing-rocket-heaters-safely/

This applies to ALL rocket heaters.

Mark Kansburg : 1st things first, because you are a visual learnerI will send you to a spot to talk About what the Transitional Area is, and is not! HOWEVER-
the Castable core you will be looking at is a failure, When someone Else makes a Castable Core that works and is for sale theirs will look like Dragon Heaters,
Dragonheaters.com!

Go to the listing of all posted Rocket forum Threads and locate ''Rocket Mass Heater Shippable Core'', and look at the Third picture. the square hole in
the center is for the Heat Riser, The big ring is for the Rim of the over turned Barrel, and you have an arc of about 300 degrees for the insertion of the
horizontal pipe to carry to hot exhaust gases through the Cob Thermal Mass, the inner ring and the horizontal hole plus your 1st clean out make up the Whole
of your Transitional area Big Al !

Late note: By Paul W.s own hand we are told this line of research has not produced a finished product. However much has been learned! -I think we will have
to go modular building it piece by piece or just go back to bricks !

MY POINT IS to Qoute Winston Churchill on the evening of the Normandy Invasion June 6th ! "This is not the End' 'this is not the Beginning of the End !''
'' It Is the End of the Beginning '' (we Hope !) Mark ME down as ''For the good of the Craft'' Big AL !
''