Heather Arvensis

Thanks peter! We have been back at the drawing board trying to come up with a better design since putting the barrel at the end of the bench puts it too close to too many combustibles. It could be doable but a pain. So with all the potential problems of that original design we are trying to come up with a new design entirely. There are windows and doors everywhere… a tree trunk in the middle of the room… and the exhaust is already installed so lots of variables to work around. What if we did something like this quick, not to scale sketch? Since we are building mostly with cob I can do a bench wider at gas receiving end and narrower at the other end. I would maybe need a baffle or wall between barrel area and exhaust since this design would have barrel in front of exhaust?
(I’m not sure on exact measurements of width yet as that can be adjusted to hit the desired ISA. I would also need to get creative with supporting such a wide bench top span. I do have rebar, angle iron and bricks for towers!)
I do like the backrest bench design you did! We are still pondering that idea.

Thanks for the tip on including the barrel in the ISA… does that apply to jtube builds as well?

Cheers!

Peter van den Berg wrote:

Heather Arvensis wrote:I’m currently working on my second RMH build. Last year I did a j-tube and now I’m working on a 6 in batch box. The bench/strat chamber will be an L-shape with firebox on one end and exhaust on the other. In an effort to have the burn chamber where we want it to land, my internal measurements would be a bit small to stay within the 57 ft2. (Contrary to my lovely, sage teacher and mentor, I prefer not to install a bypass 😊). The internal measurements I would like to do are-
12 inches tall
13 inches wide
(Length is approximately 114” on one leg and 90” on other)
This would create a small but long chamber… does anyone know if there would be any negative aspects to this shape?

To be frank, it won't work at all. Just a quick calculation shows  that the Internal Surface Area would be close to 80 ft2. Far too large, according to the recommended values. The L-shape of the bench makes matters worse, lots of friction is expected, due to that sharp bend.
How do you plan to lead the gases from the combustion core into the bench, and what variant of core do you want to use?

Hi Peter! I’m so grateful you chimed in!
I’ll include a rough layout photo for reference. I re-ran my numbers just now, twice. I’m getting 53.66 sq ft for the numbers in the photo. And 56.74 sq ft for the layout in original post. 🫣 Now, if my brick cutting today is any indication, I am totally bad at math… 😬
(I did subtract the floor… is that not ok??)

As for the L shape- I had no idea that would pose a problem! I got away with it for my j-tube but maybe because it goes from barrel to transition area to into Strat right next to corner… shoot. What if I made the corner wider (less cob there) to help relieve friction?
As for leading gases I was planning on going into barrel from riser and dump straight into bench with as wide and big a hole I can manage.
As for variant of core I’m not quite sure what you are asking… type of batch box? If so, I’m doing the basic, original design.
I sure do appreciate your expertise!
Cheers!

Hello all!

I’m currently working on my second RMH build. Last year I did a j-tube and now I’m working on a 6 in batch box. The bench/strat chamber will be an L-shape with firebox on one end and exhaust on the other. In an effort to have the burn chamber where we want it to land, my internal measurements would be a bit small to stay within the 57 ft2. (Contrary to my lovely, sage teacher and mentor, I prefer not to install a bypass 😊). The internal measurements I would like to do are-
12 inches tall
13 inches wide
(Length is approximately 114” on one leg and 90” on other)

This would create a small but long chamber… does anyone know if there would be any negative aspects to this shape?

Cheers and thanks!

Hello!

I’m trying to find out if horticulture perlite (not treated to be water resistant) is ok for the base insulation under the RMH or must it be the masonry perlite? I will be building on top of a loose rock floor. It’s about 3 inches of various sized rocks getting smaller in size with depth. Under the rock layer is sand. There is not a vapor barrier but I’ve never seen any moisture- although I do live in the Pacific Northwest .....
This question has been asked in this forum before but it went unanswered?

Also, any suggestions on what to do for a base under the mass? Build right on top of the rocks? Do a perlite pad on top of the rocks?In an old post, Erica suggested a semi- dry stack as the first layer to help with keeping things dry. Unfortunately, she didn’t give any info on how or with what material?

Thank you!

thomas rubino wrote:Hi Heather;
Welcome to Permies, and Welcome to the wonderful world of Rocket Science!
For how to books on Batchbox construction see my website https://dragontechrmh.com/
I offer them in hard copy or digital PDF format.

Let me start by saying I believe an 8" J-Tube will make you much happier than a 6" will.
An 8" uses larger wood and once warmed up will only need fuel every 45 -60 minutes.

Barrels) You only need one, preferably with a removable lid.
Or you can build with no barrel at all if you have plentiful clay bricks to create a brick bell instead.

Your horizontal transition area is easy to create with clay bricks. (Much easier than custom cutting a barrel)
The back 1/3rd of your barrel sits over an empty clay brick box.
Hot air leaving your riser sinks around the outside of the barrel it settles down into the brick box.
Your pipes or your hollow bell start from the brick "mini" bell.

You will only want firebricks on the floor, in the feed tube, burn tunnel, and the first 16" of the riser.

A five minute riser is the fastest easiest way to go, it sits on top of the firebrick riser and is sealed with a fireclay mortar (cob).

Your beach clay will work fine as a cob mass, however, a brick bell is a more modern choice than a piped mass.
Fire clay and a screened graded sand work best for mortaring bricks.

A 2x4 frame filled with 3.5" of a perlite clay mix, is enough to insulate under an RMH
A common method to build on top of wood floors involves using clay bricks set flat on the floor.
A cement board is set on top with 3.5 inches of perlite clay as a base to build your core on.

As you may have noticed there are quite a few upgrades and changes that are now common in RMH construction that are not in the Wisner's Builders Guide.
You can find information on new innovations in the RMH forum or on my website.

Well hell! Just when I was feeling slightly educated enough to pull the trigger on a j-tube, vented mass stove. Now I’m taking a second look and diving deep into the batch and bells. Which definitely make more sense for me…. But damn… do I have time to start over in the planning department?!
One thing I’ve noticed within the forums is how quickly one great idea is no longer….. but the no longer part is not always easy to find.Hence why I was thinking of sticking with tried and true. However, the bells and batch models appear to be sticking around. Between your site and products, walkers and Peter I ought to be able to figure it all out?!
🤷🏻‍♀️
I need to learn more about the “skins” and how to do that with cob or rocks instead of 600 bricks.
One question for now-
Are walker’s CFB cores still a good choice? If remember correctly, you didn’t like them in the feed tube due to the abrasion -but I like the simplicity of them. Do they have the same concerns as the hazardous ceramic blankets?

I will go back down the rabbit holes and return with a slew of new questions I’m sure!

Thank you!

Greetings! I’m finally going to make my first rocket mass heater- two in fact! I’m definitely hitting analysis paralysis…
I was planning on 6 inch, j tube style heaters. (I would prefer batch box but my understanding is they are more complex and there isn’t a solid “how to” guide yet?? Any suggestions?)

Both buildings are small, 400-500 square feet. One will be well insulated the other is poorly insulated.
They will be the only heat source in western Washington state weather.

Here is my first list of questions in hopes to at least get started!

(I live on an off-grid island in the Pacific Northwest. Obtaining materials is starting to dictate what and how I do things on this project.)
First off, the firebrick is going to be multiple boat loads. In an effort to reduce the number of bricks I need I’m leaning towards the 5-6 minute riser. Since that goes off script from “the book” I’m struggling to understand how the base of the riser connects with base of the burn tunnel/core inside the manifold? Any links, videos or threads on that part of the construction?

On that note, the manifold…. Barrels are a b @$?ch to get out here (I won’t bore you with all the details but the fewer the better I think?). I’m starting to entertain the idea of building the manifold with regular brick. Again, off script from the book! Any suggestions on if this is difficult to do?! I’m having a hard time finding a clear “how to” on this part. (However, maybe two more barrels are easier to get on island than more bricks?! Phew.) I guess the question here is which material is easier to build from? And any instructions on the brick version would be swell!

On to clay questions- I have an unlimited source of what I think is glacial, marine clay. (Cliff side of land meeting the ocean. It’s light grey when dry and dark grey when wet.) It performs well in my thermal cob samples. I think it’s completely viable for the cob mass but what about the slip and mortar? Is there any way to know if it will hold up to being “glue” between the firebricks in the core? Is it best to play it safe and purchase some known fireclay?

Next up is rmh foundations.
One is going in a room that already has a rock floor. It is beach rock of larger size on top and gets smaller as it goes down. Probably about 3 inches of rock and pebble and then sand and earth below that. Do I need to put an insulated layer under the mass to keep the heat from going to the earth and below? (In addition to the perlite/slip that I will put down under the core.)

The second rmh is going in a cabin currently being built. It will have a wood floor but we can do whatever needs to be done under the heater to protect and support. What suggestions do you all have for how to insulate from the sandy ground and the sides next to the wood floor? Can I build the floor up from the ground with cement or broken concrete blocks to get the heater up to floor level?

(I will try to add photos of both floors.)
My head is spinning but I want these heaters too much to give up yet- any help would be greatly appreciated!
Cheers!
Heather