Are you interested in building a rocket mass heater? What is holding you back?

I have loved learning about RMH and would love to have one.

If only I lived in a bigger house...

I guess I could get some #5 cans and fashion one out in the yard though that would only be a rocket stove.

Glenn Herbert wrote:Code even says that a masonry heater needs to be supported directly by masonry piers or foundation and not wood

What is the code that covers this?

Glenn Herbert wrote:Heating rooms distant from the heater location could be tricky, and we can only advise usefully with a floor plan of some sort and/or good pictures.

I'd like to do that tho it feels like leaning on you'all quite a bit.
As for  no wood floor under a RMH that sets me back, not even with a sheetmetal barrier like I have under my woodstove?

Glenn Littman wrote:...What is holding you back?

I live in Maryland and I would love to connect with someone who can help me build one. I can't put it in my house but I want to build it outside (maybe build a structure around it) and connect a heat pump to it to heat my house in winter. I have an unlimited wood supply.

Ian Graham wrote:As for  no wood floor under a RMH that sets me back, not even with a sheetmetal barrier like I have under my woodstove?

If the top of masonry foundation walls is close to the floor level, you could place steel rails diagonally in the corner and build a concrete pad. This solution is used in Europe when building a masonry heater in the room corner when the floor is too weak to carry such a load.

Barriers to starting:
-we have a high efficiency woodstove installed;
-good access to hardwood cordwood; less effective access to small stuff
-intimidated by evolving abbreviations & terminology (J-tube, K-tube, riser, bell...);  a pegged glossary/wikidictionary would help
-enjoy view of flames and intimidated by options to install a window
-confusion over naming & accessibility of supplies (refractory brick, clay for cob, insulation etc.)
-until recently, limited time; cob construction looks fun in timelapse youtube, not sure about irl

I may still try something next spring.

John C Daley wrote:In Australia I am held back by lack of concrete information.
I habe been advised by members on this site about what type and size I need to build.
But detailed information about build plans are very hard to find.
I have ascertained from batchheater.eu what dimensions I need but that is all.
I would love detais for a 125mm [ 5 inch] batch rocket  unit.

This is the issue I am facing (here in Pennsylvania USA in 2026). I have purchased several books (some through permies) and watched many videos (some through permies), and I'm still having a hard time finding concrete information laid out for a newbie. I'm a handyman/carpenter by trade, so I know how to use tools and a tape measure. What I need is a detailed set of drawings of how to make one of these things out of fire bricks. It doesn't inspire a lot of confidence in the product to have a bunch of people experimenting on camera saying, "You can build this!".

Half the websites dedicated to rocket stoves are defunct--even ernieanderica.info takes me to some foreign landing page with a soccer ball on it. It seemed Ernie and Erica were the go-to people.

A lot of the permies RMH videos talk about a "shippable core". I'd love to get my hands on one of those, but where? Did the kickstarter lose steam and no one bothered to update the published information on permies?

The only real plans I've seen are the batchrocket.eu plans, and even those have limitations (I have to interpret a Sketchup drawing on a free website).

Am I missing something here in 2026? Please tell me I am!, cuz I'm hoping to build a RMH (batch box style) this summer. But maybe I'm asking too much at this stage--just hoping for it to be less experimental, I guess.

Hi, interesting thread and great question.

I have been wanting to build a RMH for a while now,
even though I have a tiny tiny house in a rather hot climate. We do have cold winters (night time moslty).

The thing that holds me back to embark, besides lack of time and all such things
is the materials.

I would love to build one where I do not have to use the special heat resistant whatchamacallit for the core.
I _do_ understand why it's needed, but always end up taking a liiiitle time (which I lack) to try to find alternatives
or find what they used in the mass heaters in central/northish Europe.
They did not have those materials back then, but I did not find any good resources yet on how they build their kachelovens or masonry heaters.

I bet there's tons of info out there, I just always end up looking over it, or again, lacking time to do the research proper.

Another material-related thing is the insulation below the RMH.
The floor is basically a big boulder/rock, and initialy I had not given it any thought to have insulation and build the RMH on top of it.
Now that I know that, I find myself thinking about a thick layer of wool, with all the questions that brings with it.

So not lack of space or time to build, more analysis-paralysis about the materials and being stubborn on the core super tech material...

One day!

Dalo,

You just use the firebricks for the core and it will work. If you insulate the riser, it will work better and if you build the upper part of the riser from insulating bricks, it will work even better. It can evolve further into building entire core from insulating material, but it's impractical, due to its fragility and softness, so the compromise is chosen - hard firebox and soft upper part of the riser.
Before the invention of modern firebricks in late XIX century, regular bricks and cob were used for the purpose of building heaters. Even in older times people were aware that some clays are more refractory than others and various bricks were used for various tasks.
And now it's easy to purchase quality and uniform refractory material.

Hi Cristobal!

Thanks for your splendid answer, very much appreciated.

I would love to ask some follow up questions (try to keep it short)

- do you just stack the firebricks? or need some goop between them?
- insulating the riser with rock wool or is that too low temp stuff?
- the top insulating bricks that's that funny whatchamacallit white material right?

Yes, evolve, my intention is to build one which can be "easily" disassembled and upgraded,
and builing the first one outside.

Darnit, now i have less excuses, and want to start building :)
Perfect ! I love this forum!

dalo franss wrote:- do you just stack the firebricks? or need some goop between them?

If you dry stack brick, thermal expansion will quickly move them around and will open the joints. It would work with a well designed tension frame, but would work better if the dry stacked bricks had thin layer of refractory wool in the joints. For testing, dry stacking will work fine, especially if brand new (straight and square dry pressed, not extruded) firebricks are used.
The brick can be mortared with:
-clay/aggregate mortar - air setting; can be reused
-or hydraulic mortar - water setting based on alumina cement; can not be reused
Tension frame is a good addition even if mortars are used.

dalo franss wrote:- insulating the riser with rock wool or is that too low temp stuff?

Outside of the riser the temperatures are much lower than inside. for example a brick that is almost too hot to the touch at 70 C, it will be 450 C on the fire side. i do not know if people use it, but I think it would work.

dalo franss wrote:- the top insulating bricks that's that funny whatchamacallit white material right?

Yes. They are insulating bricks. There exist various kinds and not all of them are designed to work in the flame path (perlite or calcium-silicate).
The most popular insulating firebrick ARE designed to work in the flame path. For riser it's recommended to use IFB-2600, rated to 2600 F. They can be purchased at well stocked refractory supplier for $6 a piece (US made).

dalo franss wrote:Yes, evolve, my intention is to build one which can be "easily" disassembled and upgraded,
and builing the first one outside.

Building a prototype outside is the best approach. You will learn a lot and risk nothing.

I have drawn up a plan for one for our place in Arkansas Mountains, but have Not begun yet. I have a question about the Mass Heater portion of pipe. Does the pipe have to be perfectly horizontal, as I have it drawn with slight incline for each leg, which brings me to the 2nd question. I have approximately 32 feet before chimney entrance which is approximately 30' but have 3 180 deg turns as I have 4 runs drawn into the bench area, with chimney near combustion chamber barrel to help draw. Is this too much length. Please see illustration. Pipe is 6" w/ 1/8" wall

Rocky Massengale wrote:I have drawn up a plan for one for our place in Arkansas Mountains, but have Not begun yet. I have a question about the Mass Heater portion of pipe. Does the pipe have to be perfectly horizontal, as I have it drawn with slight incline for each leg, which brings me to the 2nd question. I have approximately 32 feet before chimney entrance which is approximately 30' but have 3 180 deg turns as I have 4 runs drawn into the bench area, with chimney near combustion chamber barrel to help draw. Is this too much length. Please see illustration. Pipe is 6" w/ 1/8" wall

. I need a little advise for this configuration considered before commencement of construction.

Rocky Massengale wrote:

Rocky Massengale wrote:I have drawn up a plan for one for our place in Arkansas Mountains, but have Not begun yet. I have a question about the Mass Heater portion of pipe. Does the pipe have to be perfectly horizontal, as I have it drawn with slight incline for each leg, which brings me to the 2nd question. I have approximately 32 feet before chimney entrance which is approximately 30' but have 3 180 deg turns as I have 4 runs drawn into the bench area, with chimney near combustion chamber barrel to help draw. Is this too much length. Please see illustration. Pipe is 6" w/ 1/8" wall

. I need a little advise for this configuration considered before commencement of construction.

You can see that center section is vertical whereas the feed section from combustion into it is slightly angled and discharge end is slightly angled to provide draw to chimney. Feasible ?

Advise on design would be muchly appreciated

Rocky Massengale wrote:

Rocky Massengale wrote:

Rocky Massengale wrote:I have drawn up a plan for one for our place in Arkansas Mountains, but have Not begun yet. I have a question about the Mass Heater portion of pipe. Does the pipe have to be perfectly horizontal, as I have it drawn with slight incline for each leg, which brings me to the 2nd question. I have approximately 32 feet before chimney entrance which is approximately 30' but have 3 180 deg turns as I have 4 runs drawn into the bench area, with chimney near combustion chamber barrel to help draw. Is this too much length. Please see illustration. Pipe is 6" w/ 1/8" wall

. I need a little advise for this configuration considered before commencement of construction.

You can see that center section is vertical whereas the feed section from combustion into it is slightly angled and discharge end is slightly angled to provide draw to chimney. Feasible ?

Advise on design would be muchly appreciated

 I forgot to mention that cleanouts have been added at 180's to clean out Horizontal runs, and that Barrel is Schedule 20 SS 24" pipe 36" long will be building manifold as suggested with IFB-2600 Brick and wrapping with perlite to about 2 - 2 1/2" from the barrel cap at top.

The design looks workable, but most builders are now opting to make a stratification chamber instead of a piped mass. The main advantages are less flow restriction and susceptibility to ash blockage, as well as being easier to clean out when necessary.

Are you saying that another large chamber like what the one with j firebox n manifold are in? To take the discharge of that into another chamber at say mid level and then allow the heat to stratify and discharge to chimney near bottom ? OR SOMETHING ELSE ? ARE THERE PICTURES OR DRAWINGS AVAILBLE SOMEWHERE ?

By the way phil,
Thanks for responding ?

Yes, a stratification chamber or "bell" is just a hollow brick box with the combustion core feeding into it, and the exit to the chimney leaving from near the bottom of the cavity. The new hot air rises, gives its heat to the brick box, and falls as it cools. The coolest air ends up at the bottom where it leaves for the chimney. The internal surface area of the box needs to be sized to extract the right amount of heat for best operation, per instructions at batchrocket.eu.

Rocky, I am a beginner,
but  one thing i  have learned:  the long runs with 180s are not optimum. Too much friction for exit gasses I think.

A bell (or stratification chamber)is superior, and can be cob or brick or even made using earth, in a pinch.  

Thanks Rico
i have received loud n clear !

I haven't found the perfect setup and the aesthetics of the current models make me hesitate. I lost the information for the man who has built a system that can be purchased and completed at home. It had the option for an oven. He uses brick for the heating systems. There was a video where he came to a customer's home and helped build it but I lost that link. I think if it was done with brick like some of the Russian/Eastern European videos we see I'd be more willing. Our homestead land has some smaller trees but is not a big forested area so a rocket type stove is ideal but the actual look isn't palatable.

There's a YT channel that has Medieval techniques that I've been watching for ideas. They have some really great models that have been lost through time.

BTW I did buy the rocket series DVDs that Paul Wheaton put out to see if anything new was coming down the pike.

Thanks Sandy, Still working out Details for the Upcoming build !

Here is a link to Matt Walker's stoves
https://walkerstoves.com/
He sells brick-by-brick plans for cook stoves, water heaters, BBQ's, and more.

This is probably Sandy's lost link.
Matt used to travel to build but I think he has stopped doing that.

Thanks Tom,
I hope it helps Sandy, at least my communiques with (Rocket Scientists) about details for a solid build that functions well ! I am a hands-on guy and want to build my RMH myself, I have been in construction most of my life (Residential, Commercial and Industrial), I am not familiar with RMH construction but asking and acquiring all information possible to "get her Done" . I am confident that after all the videos/research/questions asked and answered, that I can create a great RMH at my place that I am in process of building !  

Any issues with this design for a 6" system ?

An important thing to be aware of is that a J-tube system has much less power for the size than a batch box. It has been found that an 8" J-tube is roughly equivalent to a 6" batch box in rate of heat delivered, so using the bell size for a 6" batch box needs an 8" J-tube to heat it adequately.

My experience is that in a space/chimney with good natural draft, an 8" J-tube is well served with a 6" final chimney leaving the bell.

Good Info will Redesign for an 8" can I still use a 6" chimney pipe discharge ? i already own it !

Apologies, i didn't finish your post until I asked the stupid question about the chimney pipe !

Am Good to go then ! the J tube was gonna be a fabrication from ceramic fiberboard and fire bricks anyway so that is Great to know BEFOREHAND !

From the look of your plan, with the chimney rising straight through the central peak of the roof, I would expect a 6" chimney to work. This assumes that you don't have weird atmospheric or environmental conditions.

Thanks Glenn

it will be right out The Peak, I will be living in the Mountains of Arkansas, and the wind does do some whipping around, but the stacks will be well above the ridge !

Rocky, nice sunset photo, looks like southern Ozarks. Had one trip there....my dad took me along for a 6 day paddle on the Buffalo and white rivers , i was 12.  Serene camping spots and fresh trout for supper. Good idea to build there, sir

Thanks Rico, We Love it there, peace, quiet n solitude ! Lots of Critters, All kinds from Bear, Deer, Elk, Mountain Lions n all the rest !