All-masonry/All-brick longer term RMH design inquiry

Ernie and Erica, thanks for your work and willingness to share and teach. I have watched all the videos I could find, read the book on RMH's, listened to the podcasts, but have only found the time to read some of the threads here, partially because there just are so many. I have wanted to ask yours, or anyone else's, opinion on attempting to build an all-masonry RMH. I'm a DIY kind of guy and love the affordability and accessibility of the 'barrel rocket heater' approach. But I also really like the idea of finding a more longer-term durable design using masonry materials, as I believe was suggested at one point in one of the podcasts. I know that there are now shippable core designs out there (with manufacturing in the works) which I'm very excited about, but they are probably still designed to be used with the barrel approach...I could be wrong.
So I think what I'm asking are 2 things:
1. What do you envision being the most responsible/cost-effective design approach that uses all masonry or all brick, etc? I'm still assuming that the metal duct for the horizontal run and exhaust could be used of course. Essentially, what's in between the RMH barrel designs and full blown $5-10,000 Masonry heaters?

2. I'm pretty sure you know about Larsmith217's All-brick RMH design on YouTube, which is a google sketch-up design that he sells. What do you think of his design and dimensions? Have you purchased or has anyone else offered to purchase one from Lars for you to take a look at. It looks well done, but I see all these things as benefitting from communal efforts and perspectives and by no means want to discredit any of the work that Lars has done. He discusses the dimensions on the video I believe. Any possible improvements? What would keep this design from code approval? It it still the lack of a UL approval stamp even though fire brick is a standard well known building material?


thanks again and sorry if this has already been addressed before. I can't wait to see your RMH DVD and the 4 DVD Rocket Stove workshop with Paul. Of course I supported them both.

Josh, I did post this same question, and was told that the barrel is absolutely necessary because it is metallic!
The good conduction of the metal makes the high temperature of the smoke coming through the inside rise fall down dramatically, thus helping the draft because the colder smoke will go down on the sides.

So, with all masonry, more smoke at the beginning, more need of a good outside smoke exit, or a need of electric ventilation as seen on this video it seems.

Xisca Nicolas wrote:Josh, I did post this same question, and was told that the barrel is absolutely necessary because it is metallic!
The good conduction of the metal makes the high temperature of the smoke coming through the inside rise fall down dramatically, thus helping the draft because the colder smoke will go down on the sides.

So, with all masonry, more smoke at the beginning, more need of a good outside smoke exit, or a need of electric ventilation as seen on this video it seems.

The amount of smoke has to do with the combustion chamber. Perhaps you are referring to exhaust and not actually smoke. The barrel does not determine if there is smoke or not, only if the heat is radiated immediately or not. It is possible to have a rocket heater without a barrel that is all masonry material. It is the responsibility of the chimney to exhaust the gases. You must have sufficient surface area to absorb the heat w/o a barrel, or it will exhaust to the chimney, wasted. There is the tricky bit.

All rocket heaters should have a good chimney for reliable performance.

I was not refering to exhaust but to heat riser and barrel.
Call it smoke or gas this is not the problem, I was referring to the metal inducing conduction/radiation, causing temps to go down, thus "smoke" colder thus going down -> creating draft.

What you say does not correspond to what others said,
But I reckon that the book does not say all what would be useful to free us from following recipes (=plans)!
If we could agree so that we could all adapt the basic principles to our personal constructions criteria... but masonry instead of barrel seems to not work the same.

The barrel determines if the heat is radiated immediately or not.

True, and this radiation removes heat, and makes the draft because gases go down easier after the heat riser, in the barrel.

You must have sufficient surface area to absorb the heat w/o a barrel, or it will exhaust to the chimney, wasted.

Half true but half wrong. You mix 2 things.
The mass from the bench or whatever absorbs the heat. It can be all masonry.
This is not the main utility of the METAL barrel.

It is the responsibility of the chimney to exhaust the gases.
All rocket heaters should have a good chimney for reliable performance.

You also mix 2 things here.
The chimney is only an exhaust pipe.
It does not do what usual chimneys do. The exhaust has nothing to do with draft.
RMH are supposed to be able to do well with only an exhaust in the wall.
Then, for legal reasons you can be forced to use a real chimney.
A common chimney will also eventually compensate a design that does not work well...

The REAL CHIMNEY of RMH is the heat riser.
By real chimney, I mean what creates draft.

A common chimney does 2 things: exhaust gases and create draft.
A RMH separates those 2 purposes between an exhaust pipe and a heat riser.

Xisca Nicolas wrote:So, with all masonry, more smoke at the beginning, more need of a good outside smoke exit, or a need of electric ventilation as seen on this video it seems.

I explain better:
- More smoke at the beginning = above the mouth feed, when you light the fire
- More need of a chimney OUTSIDE = for draft as in a normal stove.
- Or ventilation = to compensate and help to create draft.

All these drawbacks come from only 1 thing: it is no more a pure rocket because the internal chimney does not do its job well when it is not metallic.
I recall that the rocket pushes gases Vs a chimney that suck gases from outside.

Xisca and Sandy : This will be a two parter where I jump in on the Functions of the Combined Heat Riser and 55 gal Drum ! and A short comparison of Masonry Heaters and
Rocket Mass Heaters R.M.H.s, and Hybrids !

This is only my latest interpretation of what goes on within the Heat Riser, (which I think we all agree works as a 1st, primary chimney) and the Barrel, and the words are my
own, I claim no special knowledge! Everything said here relates only to the functioning of a Good R.M.H. !

Not only does a Well insulated Heat Riser create the High flow rate, high Volume flow of Hot Exhaust gases, these hot exhaust gases by their very nature is/are packed with
'potential energy' !

The rapid cooling of the until then Hot Exhaust gases, from their contact against the skin of the Top and sides of the Barrel, allows them to fall rapidly through the transition area
and flow out the horizontal pipe ! The turbulence created within both of these sections creates both more heat, and the Rocket-y sounds that you hear !

Failure of the External skin of a R.M.H. to radiate sufficient heat will eventually cause the Flow of the Hot Exhaust Gases to stall as the temperature within the R.M.H. equalizes
everywhere ! This is even more pronounced when the Heat Riser is poorly insulated, as enough heat can then leak through the Heat Risers External wall - into the area of the
barrel or exterior skin of the R.M.H. to cause that 'stalling' to occur at a higher temperature and sooner ! Massive fail, and a living space filled with smoke !

Again, everything said to now relates to the R.M.H. ONLY ! - -

The original build discussed at the start of this build is a think- outside- the- Box Combination or hybrid Masonry and R.M.H. Unit, and does work, as a D.I.Y. Project, built on the
cheap, it is an interesting build!

There is certainly room here in the combined Wood Stoves Forum Threads for more discussion of Masonry stoves, and I am truly in favor of seeing more of it, This Model by being
'a horse of another Color' actually confuses the discussion, A report from him on how his 'Wood Stove" continues to work would be useful to this discussion - With out more info
we are all like the Blind men attempting to describe an Elephant ! I hope this helps clarify a simple but important point !

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

So, how often does the barrel have to be replaced? I assume you shouldn't "encase" the barrel in cob or something then either...

Danette Cross : A look in your phone book and a couple of calls should convince you that the 'Heat Exchanger'[ on a Conventional Fossil Fuel Fired Furnace is usually guaranteed
for 15 - 20 years with most of them being Rated for the full 20 years of service !

Having said this with over ~100,000 working Rocket Mass Heaters ~ having been built to date, Where are the reports of the failures? AND - the most often recommended
55 gallon drum, by myself- and others - Is the barrel with the removable top, held on with a clamping band, over the years the thickness of all 55 gal drums has diminished,
with my favorite , most recommended, barrel still made out of thicker metal than the afore mentioned F.F.F.F. heat exchanger!

Allowing for the fact that most Rocket Stove 55 gallon drums were made in the past with thicker metal gages of steel, I still expect to see 15-20 years out of the R.M.H. I put
into service this fall ! for the Good of the Craft ! Be safe, Keep warm!

As always, your comments and questions are solicited, and Welcome. Think like fire flow like a gas, Don't be the marshmallow ! PYRO - Logically Yours - BIG AL !

Late note, yes you can easily Cob the bottom 1/2 of the bench ! A.L.

Allen: Well, we will go to Axmen's and see if they have a heavy duty barrel. They are a very good place to go for alternative energy materials. I have 2 barrel racing barrels on the place that I will check to see if they seem sturdy. Racing barrels can usually stay standing after a good "rub" by horse and rider.

One more question: we have a 33'x48' metal building that we are going to convert into a house. That gives just the 1st floor a footprint of 1584 s.f. When the loft is included it will be around 2376 of living space that we will need to heat (Montana winters can be a tad bit chilly). So, do you have any figures on what type of dimensions we should consider, and how much thermal mass we should encorporate into the design? I have seen a photo of an RMH that had cob surrounding the barrel, with the top left alone for a stovetop. I realize that would mean that you don't get the "immediate" heating that you do with an exposed barrel, but I did like the look of it.

Danette Cross : Go with the 8'' system, you didn't mention how high/tall the interior space is or what material the floor is made out of !

This is your build but you still have time to take in more information as you gather materials, a thin layer of cob can be made nearly any color you would like.
a thin layer of Cob will still radiate a sufficient amount of heat !

I took the time to bump up the Forum thread 'Oil drum in my Living Room '' '' '' ''! ' posted by Erica Wisner, I would also like to send you to ernieanderica.info
there is a tremendous amount of information useful for a 1st time builder, specifically I wanted to get you to click on 'Consulting and Booking Events' on he right
side of the Page. This will take you to a new page where you can click on the 'Site Planning' section This can be used for a nearly all-inclusive Guide to make sure
you are reedy to start your build !

Have you been to rocketstoves.com for your PDF Copy $15.oo of Evans' and Jackson's Great book 'Rocket Mass Heaters', there is STILL No other
book even equal in any Language ! With ~100,000~ Rocket Mass Heaters R.M.H.s built most of the 1st time builds were made with this book, and virtually all of
the 1st time builds that worked and are in use were made with 'The Book '! Hope this helps and is timely, for the Good of the Craft !

As always, your comments and Questions are solicited and Welcome. Think like Fire, Flow like Gas, Don't be the Marshmallow ! PYRO - Magically BIG AL

Not quite exact on the cieling height. See attached. I think the door is about 12' high so that might give you an idea- again, guessing. The floor is a 6" concrete floor with fiberglass mixed in. We want to change the roof line so it takes more of a "gable" barn shape so that will add even more space.

Dannette Cross : I am currently living in a 30' X30' House in town and will be moving into my travel yurt, 100 Sq. ft eventually building or purchasing a used 20'-ish Yurt.
I actually use less than 300 sq. ft now and In the future will be using the yurt almost exclusively to get out of the weather ! Why do you think you need so much room !
how big is your family ?

As a member of our local Volunteer Fire Dept. I can tell you that your large overhead door is a huge heat sink, I would remove the door in total and box it in with
conventional framing, remembering to have an Air chamber.

Alternately, pay an Overhead door installation Company to aline the door, and see it un- aline itself within 100 ups and downs. Our Fire Dept plans on using a 4 man
crew 3-4 hours per man To tighten and re-aline our doors every two weeks !

It is still such a heat sink that when we had a grant that paid for 60% of the cost of Insulating the station 45 % of the membership voted against it be cause '' Whats
the sense of insulating when we have all these drafty doors !''

Again this is your building and future home, live in it a while, put tape down on the floor to mark off future rooms, see how much space you actually need, Run your
own race ! I hope that you find something in this ramble that you can take to heart and use ! For the good of the Craft !

As always, your comments and Questions are Solicited and are Welcome ! Think like fire, Flow like a gas, Don't be the Marshmallow ! PYRO -logically Big AL

The door and the steel will be removed and the building will be clad in wood. I am a fiber artist, and have 6 spinning wheels and 5 looms, 2 of which are 45" wide and at leat 4' deep and up to 6' tall. The loft will be a studio and where we have a guest room. Downstairs we will have the bedroom, kitchen, bath, office for the farm operation and such. Basically, we will live on one floor, but I will work in the loft alot.

I just moved out of a small house into a smaller house, and can't wait to get into a place where I can move around! I can't even find a place to sit and spin except outside, and that just won't work in the winter. Forget setting up one of the looms. For what I do, I need room. Below is a photo of 2 of my looms set up in a 12x12 parlor in the house in Missoula. Can't imagine bags of fleeces, racks of weaving yarns, spinning wheels, tools, tables with tools - you get the idea....

allen lumley wrote:

This is only my latest interpretation of what goes on within the  Heat Riser, (which I think we all agree works as a 1st, primary chimney) and the Barrel, and the words are my
own, I claim no special knowledge! Everything said here relates only to the functioning of a Good R.M.H. !

Not only does a Well insulated Heat Riser create the High flow rate, high Volume flow of Hot Exhaust gases, these hot exhaust gases by their very nature is/are packed with
'potential energy' !

The rapid cooling of the until then Hot Exhaust gases, from their contact against the skin of the Top and sides of the Barrel, allows them to fall rapidly through the transition area
and flow out the horizontal pipe ! The turbulence created within both of these sections creates both more heat, and the Rocket-y sounds that you hear !

Failure of the External skin of a R.M.H. to radiate sufficient heat will eventually cause the  Flow of the Hot Exhaust Gases to stall as the temperature within the R.M.H. equalizes
everywhere ! This is even more pronounced when the Heat Riser is poorly insulated, as enough heat can then leak through the Heat Risers External wall - into the area of the
barrel or exterior skin of the R.M.H. to cause that 'stalling' to occur at a higher temperature and sooner ! Massive fail, and a living space filled with smoke !

Thanks for the great info

My aim is to make an efficient heater which heats up a 120 sqft and 96 sqft rooms being built into the wall beetween them. I planned a cob wall maybe bricks around the heat raiser outside...

How would you do it? How would you provide radiant heat both rooms and heat up a mass under a double bed next to the wall in the bigger room please?

To your info about the Conductiving and gases flows the cooling way(sorry for my english) would a water heating pipe in the right place create the draft? For example on the bottom of the outside of the heat raiser near the exhaustion pipe starts?

Thanks in advance
My first post

I would make a section of the dividing wall doubled, with a 12" to 16" space between them, and run the heat riser up in that space. Then I would connect to a cavity in the mass under the bed for the hot gases to flow into, and from the bottom of that cavity connect to the chimney rising to the roof.

That is the bare outline; the dimensions would depend on the details of your spaces, any doorway between them, and your heating requirements. As you appear to be in the UK where winters are usually milder than in the northern US, and the spaces you want to heat are relatively small, I think a 6" system would work fine for you. For instant radiation, I would mount a metal plate in the wall of the cavity, which would also serve as an access port for inspection and maintenance of the riser. You could put a plate in each room if instant radiation is important in both. Whether you build a conventional J-tube RMH core or a batch box is up to you; in either case, you can use the information at batchrocket.eu for component sizing and cavity layout. It is generally thought that a 6" batch box gives equivalent heat output to an 8" J-tube, so you could even make a smaller size batch box, maybe a 5" system, and get good results. If you have the room, a 6" system would guarantee that you had enough capacity, as if it is oversized, you simply run it less often.

If you give more details on the heating loads and the space layout and building materials, we can give you more detailed advice.

Thanks Sir!

I didnot really get your concept. Googleing the cavity came out as a teeth
The normal raiser size should be fine i dont want to chop the woot into chopsticks.
My question is the bell could be built by bricks partially by the same shape as a barell? With a piece of metal each room but bricks in the wall. The metal should be able to open for cleaning.
The picture is the black wood goes in the big circle is the "barell" purple is the chimney as i think right now.

I think it can work.

The house will be strawbale passivHaus windows mvhr so maybe i dont even need this other rmh i will habe a masonry rocket cookstove with bench in the kitchen.

I would like to know your opinions.
16.5 m with the walls but 4.5 plus the cellar and entrance room i will put bales walls beetween living room and cellar as well. The windows are south facing.  I will put a lot of cob into it with least straw as possible.

The house will be in Hungary middle europe. With - 20 max in winter. Not too much snow though. We are becoming dessert as i see it changing.

Okay, so continental climate, a lot colder than most of the UK. I think a rocket cookstove like Matt Walker's Tiny House Cookstove would be enough to heat your structure's area, but the house's length would make the far bedroom quite cold. I think a small batch box RMH built into the wall and feeding a space under the bed would give you comfort. A 4" system would probably give enough heat, but would not be able to handle the large surface area of the bell under the bed, so a 6" batch box system with the smallest viable wall space and a large under-bed space would do well and probably only need to be fired once per day.

I notice your plan shows windows set deeply into the south wall. This will cause the glass to be shaded much of the day except near noon, drastically reducing solar gain. I think you would get much better results putting the glass near the exterior face of the wall.

Glenn Herbert wrote:I notice your plan shows windows set deeply into the south wall. This will cause the glass to be shaded much of the day except near noon, drastically reducing solar gain. I think you would get much better results putting the glass near the exterior face of the wall.

Yeah the app is not smart enough or me... windows will be outside 50 cm thick walls so man can sit there contemplating like in movies in the kitchen kids can sit there the other side of the table when im chopping.
Inside i will put a
https://roletta-rolo.hu/roletta/tokozott-roletta/
Blind curtain in a rail? another heatbarrier.

What is that 4" system means?
Where should i put a thermosiphon water heater coil?
Can it be on the bell way down to the hole to the tubes for the mass?
Thanks in advance

A 4", 6" or 8" system means that the whole setup, from feed to chimney, is about that diameter in flow area. (Because of extra friction losses, a square channel the same size across will have about the same capacity.)

I would advise a "bell" chamber under the bed rather than tubes for the gases to flow through. See the batchrocket.eu links in my previous post for discussion of bells. This will have almost no friction losses, so it will be easier to maintain good draft.

I think the bottom of the first bell chamber would be a good place for a thermosiphon coil. Make sure there is positive pressure venting capacity, or use an unpressurized, vented system for best safety.

I have just finished an all brick 6” j designed by Matt walker who sells plans (which includes consultation to help you with the build).
It works perfectly well and I’ve run it for 12 hours straight without any issues of gasses not cooling etc.
The chimney is a different design from the type in the original rocket mass heater book
It is still a work in progress though it’s at the functional stage. Pic in the link
https://www.dropbox.com/s/1x3tm2h0ajs7yx1/IMG_3646.JPG?dl=0