Walker Stoves Brick Rocket Mass Heater Plans

Hi Permies!  I've got another plan set finished up in time for the holidays for you!   I'm excited to introduce the Walker Brick Rocket Mass Heater!



I've been having a lot of fun interacting with you all as you are building your Walker Ceramic Fiber J cores and Cook Stoves, and one of the most common interactions is folks asking for plans to build a Rocket Mass Heater using the 6" Super Hot J Core Plan.  It's such an easy way to build a core, I thought I'd try to simplify the rest of the process as well.  

I've designed a Brick Rocket Mass Heater that can be built by anyone using simple brick stacking and a safe clay/sand mortar.  The core is simple parts cut with a knife or saw from ceramic fiber board.  The brick work can be done with no brick cutting and very little fuss.  It requires about 225 bricks, ceramic fiber board, and some stone or concrete slabs/pavers for bench and bell tops.  A simple build that a rookie can build in an easy weekend, this one is for all of you folks who want an RMH but don't care for the barrel, or have a small space.  It's ideal for a small cabin, living room, greenhouse, shed, etc.

I've put the plans on sale through the weekend, there is a link to my site below for more info.

Let me know how I can help you build your heater, and thank you as always for letting me share here.  Thank you Permies!

Brick Rocket Mass Heater

Congratulations Matt !  You've done it again. If you keep popping up with these really cool plans , nobody will design & build their own anymore .... they will just buy and build yours !  Keep up the good work!

Hey gang, I know I just posted a customer build yesterday, but I got another email today and I know you all are as excited to see new RMHs as I am, so I thought I'd share.  It seems there are lots of builds wrapping up as we approach winter and I am having so much fun helping you all with your builds and seeing them come to life.

Check out this great example of the Walker Stoves Brick RMH by Joshua Heyneke:






You can see more here.

Thanks as always Permies!

Very nice Matt - thanks for sharing

Forbive me for such a pedestrian question.

What type of bricks are used for the 225 bricks necessary in this RMH? Firebricks?, red clay? Or something else entirely?

Hi Wes; Welcome to permies!
Looks to me that Matt has a row of firebrick on the bottom and then he has switched to red clay.

Wes, the brick RMH uses standard red clay brick throughout. You can buy them at Home Depot for $0.44, or check your local craigslist for salvaged bricks which is my preference.

Hi Matt, these plans look great. Since I have already purchased firebrick in anticipation of finding such plans, I'm glad they're here. How many firebricks does your plan use?

Problem is, the link you posted doesn't seem to work. It does a 404, then when I try to go through your site, I find only a directory tree in that link. Check it?

Hi Matt,
I'm really impressed with your work and am strongly considering buying plans from you.  One preliminary though:  are your brick stoves and rmhs light enough to install on a standard joist-supported floor (18" centers) or would they require some floor reinforcement or a dedicated foundation?  I gather the latter is standard for cob rmhs but is something I'd like to avoid.
all the best,
Peter

Very cool, Matt! Those are really nice examples of RMH. Exactly what I've been looking for actually. Thanks for sharing the plans. Cheers!

Is it vital to mortar the red bricks together?

It would be great to take my stove with me when I move one day?

I’m gonna presume it’s a bad idea due to heat loss through the air, but it felt like it was worth a shot.

Hi Matt. We’re planning to purchase your rocket mass heater plans, but we have a couple questions. What’s the difference as far as the amount wood used in the batch heater and the brick heater? Also, we need it to heat 2,000 sq ft, so do we modify it in some way or how do we accomplish that? Thanks!

If you use fireclay mortar, the bricks will come apart cleanly and be easily reusable. This does not meet code which requires refractory mortar, but may be practical if that does not concern you.

Heating 2000 square feet may be a challenge for any single heater that does not use remote heat transport, depending very much on the house layout; and the size of heater required depends very much on your local climate as well as the house size.

A cob or brick bench style of bell may be able to be supported on ordinary wood framing, depending on the specific details, but a concentrated tall bell will most likely require reinforcement or a dedicated foundation.

Glenn, thank you! We’re in Michigan and with our house layout we may need to do two.

In Michigan (= gets cold and stays cold) I might consider making one of them an 8" version, depending again on layout and positioning of the heaters. If it turns out to be more than needed, no problem, just burn for shorter periods each day; if 6" is inadequate, you might need to burn all day, which could be a real pain. 2000 square feet is not a "small house" which is what this particular plan is aimed at.

I might also consider building one 8" system in a central location, with provisional plans to build a supplemental 6" version in the coldest peripheral area if the first is not sufficient.

Resurrecting an older thread with a question I haven’t found an answer to…

The Walker stove build calls for 1” ceramic fiber board to cap the bell above the j tube. After reading so much about the issues with cfb and released fibers in the air possibly causing respiratory issues, I was wondering if instead I could use some 1” Superwool and place concrete slabs on top of that instead?

Thoughts for or against?

Taking the same sort of safety precautions as if you were handling batt insulation, sanding, spray painting etc applies to working with superwool or cf board.
As for capping with superwool to make a roof, it doesn’t have much stiffness to span a very wide gap and will easily sag. You could potentially provide metal supports on each side of the heat riser but they may spall and give out causing your roof to collapse.
A cast iron plate and ceramic glass from an old cooktop are some things that could be substituted as well.

As Gerry points out, most European standard ceramic fibre products are fairly safe to handle using sensible precautions however, if you should ever need to remove any ceramic fiber that has been super heated then you must be super cautious!
All the ceramic products that I use are rated as body soluble, meaning that the fibers can be broken down by our own body should they get inhaled.  
The issue becomes far more dangerous  if you inhale any airborne fibers once they have been exposed to high heat as the dust is no longer body soluble!
So you can use ceramic fibre board, although it would be best to coat it with some high temperature coating, and just be aware that if you should take the stove down, to be extremely careful of the possible dust in the air.

Hmmm, thanks for that info. On second look, not yet having the core in my hands, it appears that the riser isn’t going to be super close to the top of the bell. So, maybe the exhaust at that point will have enough time to cool a bit before hitting the cement flagstone on the cap of the initial bell containing the riser and the stovepipe?

Or, I do have some heavy firebricks. Maybe I could use those to bridge the top layer? Or maybe those and then the slabs on top adding an additional layer so that the cap is effectively two layers thick?

Firebrick above the heat riser could work. It may crack over time in such a high heat area so I would keep an eye on it.
A cement cap in this area would spall very quickly and crumble apart in no time.

Gerry Parent wrote:Firebrick above the heat riser could work. It may crack over time in such a high heat area so I would keep an eye on it.
A cement cap in this area would spall very quickly and crumble apart in no time.

Interesting then that Matt’s plans specifically mention stone or cement flagstones for capping the bell.

Being more used to a 55 gallon metal barrel, this has been very interesting buying the plans and considering he differences in building a brick/bell RMH. Wife is enthusiastic about getting it built though after seeing the videos.

I’ll try to get some in progress pics of the build, as well as getting feedback from her and kids on the effectiveness/ease of use during this winter. Hmm, have to look through the SKIP book, surely building a RMH will get me another BB…? ;-)

Leif Ing wrote:Interesting then that Matt’s plans specifically mention stone or cement flagstones for capping the bell.

As you mentioned earlier Lief, Matt calls for 1" cfb to cap the bell above the j tube. The layer on top of that then can be stone or cement flagstones for capping the bell above the heat riser.  The bench doesn't get nearly as hot so the cfb board is not needed here to protect the chosen capping material.

Gerry Parent wrote:Firebrick above the heat riser could work. It may crack over time in such a high heat area so I would keep an eye on it.
A cement cap in this area would spall very quickly and crumble apart in no time.

What about using cement bricks? If the riser exhaust will be going directly up to hit the 1” cfb, then swirling in the taller brick section before moving down to the bench, is there a problem with using concrete bricks? If so, how far down or how many layers do you think before cement bricks would be okay? What temperature does concrete spall at?

From the web:
concrete temperature tolerances

" The mechanism behind heat-induced spalling is fairly simple. When concrete is exposed to temperatures above 212 degrees F, the boiling point of water, the moisture in the concrete turns to steam. If the temperature rises more rapidly than the steam can escape through the concrete matrix, the rising pressures exceed the strength of the concrete and it begins to spall. This spalling can be explosive in extreme cases."

The cf board will take the heat above the riser but i think will eventually heat up enough to get any cement product stacked on it at spalling temps.
Clay bricks for example would stand a much better chance.
As a general rule, cement should be kept away from the core and far enough downstream to not heat at spelling temps.

Hmm, sounds like maybe I need to use actual firebricks for the top levels then, for this year… and maybe use the concrete bricks more for just the bench (layers 1-5/6? and the firebricks for layers 7-15?)

The lower layers should be much cooler. I’ll have a very limited time to build while home, before winter gets here. Not sure that I could source actual clay bricks, as apparently I didn’t pay enough attention when at Menards. My buddy said that I could probably just heat the icf house with space heaters if needed, but I don’t really want to do that!

It might depend on the actual concrete brick, certainly in my area standard concrete bricks are porous  by nature meaning that you could put one under a tap and drips would appear from the underside.
So gasses could escape too and as the bricks also hold air they wont be very good at holding heat.
However I can also buy high load bricks that have been vibrated, they might be ok.

Leif, you could also reach out to Matt with questions about recommendations for his heater.
He is very friendly and helpful.

Ok, thanks Fox and Gerry, will try to get a hold of Matt. Kinda hoping if I get mine running well and using little wood for the winter that I can inspire some other friends including Amish ones in my area… :)

Good morning permies. I've been working with the amish in my area. They seem interested but hesitant. I will say that they are always watching for smoke from my rmhf chimney. They only see smoke when I first start it up.my amish neighbor let's me know. He always says smoke for a few minutes then nothing.i would also like to say keep up the good work Mat and posting you tube videos. Always a joy to see what questions you tackle. Have a great day permies the sun is finally shining in New York gotta get something done . Probably fire wood.

Well, frustration abounds. To save time I bought a 6” j tube core from rocketstovecores.com, and on the page this guy making shipable cfb cores with Matt’s plans states to specify if you want the square/rigid riser instead of a piece of ceramic wool blanket. So I did… just opened the box and no square riser! I already had a 50’ roll of the cerawool, but went to his site and it says he is too busy to make any more cores or respond to emails! So frustrating since I made SURE to follow his instructions and he says he won’t even respond to emails until maybe fall of next year!

Hi Lief;
I was at Luke's website recently and read his message.  
You should write him.  As a  customer with a problem, he may respond to you.
No promises but it is worth a try.

Thanks Thomas, it’s worth a try. Was very frustrated yesterday with how stupid hard it has been for me to find any kind of source for fire clay in Des Moines or even Kansas City. To have such limited time at home and waste a full day then not even receive what I asked for upon opening the box was just the icing on the cake.

If I can ever get this thing built, as far as I know I’ll be the first in my county with one and a bunch are watching to see the results. No pressure though…lol

Lief;     Did you locate the Fireclay?  
I find it very hard to believe it is not to be found in those major cities!
I do sell & ship #20 boxes of Lincoln 60, but I encourage folks to find a local source.
Where did you search?

That sounds like a very bad service!
Fire clay is a normal mud, simple as that, but mud with a higher Alumina content. It  usually has whiter-lighter colour.
As Thomas points out it should be available anywhere!
Refractory or pottery suppliers sell it in dry powdered form. I get mine in dry powder bags from a local potter.
Commonly Alumina content of fire clay ranges between 24% – 34% Alumina content so look out for that %.

Tried pottery and ceramic supplies, fireplace stores and supply stores, architectural supply stores and have a lead on more firebricks… I asked them inside for ideas on where else I might look and actually may have made a friend at a pottery studio who really tried to help and can also down the road teach pottery and ceramics and 3d printing to me and the kiddos.

Fox James wrote:That sounds like a very bad service!
Fire clay is a normal mud, simple as that, but mud with a higher Alumina content. It  usually has whiter-lighter colour.
As Thomas points out it should be available anywhere!
Refractory or pottery suppliers sell it in dry powdered form. I get mine in dry powder bags from a local potter.
Commonly Alumina content of fire clay ranges between 24% – 34% Alumina content so look out for that %.

Yeah, super not impressed with the lack of service on the core kit. I wanted to e square riser so I could just pin it and go… but, the blanket is a bit too wide for the 8”x24” duct piece I bought and on top of that when I laid it out, there is a maybe 2”x2” L shaped cut all the way through the center of the blanket! Ugh, glad now I have a new roll myself so I can at least waste more supposed to be building time to return to the old house and measure and cut off my own roll a piece the proper size! This house construction is gonna be the death of me from stress… 🤪😱🤪

Are you saying that pottery suppliers dont supply clay?

Hi Lief;   What you want to locate is a masonry supply house.
This is where contractors go to buy stone, concrete blocks, clay building bricks, fire bricks, and most of all they will have fireclay.
A quick search in Des Moines brought up this  https://www.apiowa.com/
You must call them and not just search a website.
I promise you there is a supplier in that area you just need to find one.
Search for a contractor who builds fireplaces and ask him where he gets his supplies or, see if he will sell you some fireclay and bricks.
Fire bricks should cost $2-4 each fireclay should be $10-25 a #50 sack they will be available.

Thomas, thanks! API is actually one of the half dozen stores I went to. They do sell fire bricks but not fire clay. I spoke to the manager or owner and have a card for their interior sales guy. The guy with a pottery studio actually said I could order fire clay through him and he’d just charge whatever the shipping difference was and gets trucks at least weekly. I’ve got his card too.

My buddy is an ex boilermaker and has laid bricks in kilns, etc. He helped me get up to course number 9 today, only 6 left to go plus caps… gonna be a long day tomorrow.