Getting it right the first time, an 8" Batch Rocket

One of my favorite lines from early in "The Book"... "Exercise caution not only in building and operating your stove, but also in your research!" - Leslie Jackson.
The more times I read the book, the more answers I find. It's easy for my mind to wander, and I rarely get completely through a section without drifting away from some potentially valuable advise. Likewise, the more I read around, the more I find (some) sources of less than well founded advise and planning... all mixed in with nuggets of wisdom & in need of straining.

The chosen version for my first build is the 8" batch. Like many, so much reading led to so many more questions. Ultimately the 8' Batch Rocket became the obvious choice.

From an earlier line in "The Book" ... "As with most reading, it's value is multiplied by discussion with other readers." As much a gathering of plans and processes as it is the usual request for critique & commentary by a "newb", here's one more..


After much searching, Peter van den Berg's "8" rocket-thingy" grabbed my fascination. 'Well documented and the latest iteration RMH (now early 2015), one decision will be whether to use a square riser per those wonderfully shared plans:

https://permies.com/t/40007/rocket-stoves/Results-batch-box-thingy-Innovators#311498

or adapt the octagon shape from an earlier PvdB build/video:

https://permies.com/forums/posts/list/40/24658?OWASP_CSRFTOKEN=Q5KL-BX05-VSF9-O6JQ-TXEG-6PRO-19GL-BKB2#198186

I've tried to attach an image from each, but apparently may need to go back and find that "How to attach images" thread.

My build will be of insulated fire brick so either of those plans provide a great set of visuals to work with. The simplicity of the square riser or the beckon of the octagon... you may be able to sense the direction I'm leaning. After doing the math a number of times ( because the results seemed counter-intuitive) an 8" octagon actually has less CSA ( 49.77 sq in) than an 8" circle - 50.24 sq in.
so a request for comment here - square & simple? Or does the octagon shape provide enough added benefit to pursue?


Another concern - the mortar composition, especially in high heat areas. Once again - from the book...

"..wood ash, added to my local clay slip makes a really good super cheap refractory cement. It really helps with the high temperatures..." Kirk Mobert.
This, and rest of that paragraph, was worth the price of the book to me when I began to contemplate how best to stick those critical burn chamber & riser bricks together.

My (proposed) refractory mortar: re-hydrated pottery clay & wood ash. There are several old dried out blocks of pottery clay in the basement. A few days 'soak & run through a screen, add ash & mix well. One thought - might re-combining the (screened) "dust" from insulated brick cuts be a good addition to refractory mortar mix ... your comments here would also be appreciated.


In keeping with the "Keep it simple" approach, the build will otherwise mimic many "tried and true" barrel/bench designs. Nothing too out there - getting it right the first time doesn't seem like such a reach.
That it will go in an "out shop" rather than outdoors is of less concern, holding hands with ( & standing on the backs of) so many wonderful predecessors. I feel safe skipping the " first, build one outside". I have an old wood stove that will make a charming flower box... the sooner the better.

'Regards, Arlyn

Arlyn,
I'm sorry, the 8" batch box thingy doesn't sport a square riser but a round ceramic fibre tube one. The bricks are there only to fix this tube in place. Please read more of the thread of the 8" batch. When doing the riser in firebricks the octagon is better in many ways, one of those is the ability to get the double ram's horn vortex very early in the burn, even in a cold heater. The octagon can be built from firebrick splits as well, allowing a much lower mass inside the insulation. Best of all: the ceramic fibre tube. No mass to speak of, highly heat resistant and super insulating at the same time.

The insulating firebrick you mention, the light white ones are a very good second choice. The octagon doesn't need to be smaller than the round one either.

Thank you. I was just trying to re-figure my math error. Cutting cardboard pieces to scale (rather than wasting bricks) revealed the error in my thinking. Now I'm getting a CSA of 52.72 sq inches for the 8" octagon. I recalled your mention of the octagon enhancing the double ram's horn, part of why I was leaning that way.

Thanks again!

Arlyn, about the pottery clay, how dry is it? I.e. if it is completely dried hard then it may be faster to pulverize the stuff into powder. Then make your mortar "mix" with it as one would with powdered fire clay etc.

Arlyn Gale wrote: One thought - might re-combining the (screened) "dust" from insulated brick cuts be a good addition to refractory mortar mix ... your comments here would also be appreciated.

To my knowledge, yes, that would be an excellent grog.

This quote from the article (taken from a chemistry handbook) supports my reservation about the mud:
"The strength in the dry state increases with grog down as fine as that passing the 100-mesh sieve, but decreases with material passing the 200-mesh sieve. "
I don't know how fine all of this material is, but I suspect there is a lot of ultrafine dust.

It's about time I report back. The title should be amended to read ..."6 inch batch rocket". In retrospect, down sizing was the right move. The entire build was with 2800* insulating firebrick - ~97% in accordance with Peter van den Berg's dimensions & diagrams. A single barrel "quick heat" system for now. The chimney stack is the old 15' wood stove vertical (with ~2' horizontal). The results are absolutely impressive. A load of wood that might have yielded 60-70*F in the old wood stove now easily brings the (375 sq ft) shop to 80-90*F. Outside temps hovering near freezing at night. I'd estimate wood consumption is down by 75% or more. 'Kind of disappointing when I'm in the mood to tend a fire...

Thank you Peter, for sharing. Anyone contemplating a batch feed RMH would do well to heed your advice and directions!

Aryln, thanks for the update. I always wish more people would give results of their new builds after using them a while such as how much wood and amount of heat put out compared with the old stove. I want to build an 8" batch stove next spring or summer and it's good to hear that they put out more heat than a regular metal stove. I am in interior Alaska and can't afford to mess around when it comes to heating the house.

Arlyn Gale wrote:It's about time I report back.

Awesome, thank you!
Can we see some pictures?

Phil, I suspect you'll be very pleased with an 8" system. I found the 2nd link in my first post to be very useful - again: (scroll down & activate the video)

https://permies.com/forums/posts/list/40/24658?OWASP_CSRFTOKEN=Q5KL-BX05-VSF9-O6JQ-TXEG-6PRO-19GL-BKB2#198186

Mike - Any pictures I may manage to share will pale in comparison to the video in that link. Right now it's been 12 hours since the morning burn, and the RMH is still a bit to warm to pull apart for pic's. I followed the "layer by layer" diagrams provided in the beginning of the video. Watch it and I'm sure you'll agree! (Pause, copy, paste, repeat!!!)

a couple more...

Funny isn't it? I've made the drawings a couple of years ago and the guys who were filming the workshop found it worthwhile to picture the layer by layer method. Every now and then this video and/or the pictures in it are passing by, leaving me grinning like a Cheshire cat...

Some questions addressed to Peter van den Berg:

Dear Peter,

I watched several of your videos in the internet and find them very interesting.
Some questions remain:

1. Please have a look at the attached pictures. One is from Sketchup and one from the corresponding video (“Accumulating kitchen range”). I marked some bricks. They look different from the others. What are they made of? Why did you use them at this place, i.e. what special properties do they have? Are they commercially available? Where?

2. In one of your posts at Permies you say: “... a round ceramic fibre tube one. The bricks are there only to fix this tube in place.” Can you tell me (us) a little more about this tube? Where to buy it? I am in Germany this days.

3. Did you ever use bricks of Iron oxide (magnetite, hematite or something like this) in construction of masonry heaters? If yes, why, what are they good for?

Thank you very much in advance for answering these questions!

Peter

Peter Peterson wrote:I marked some bricks. They look different from the others. What are they made of? Why did you use them at this place, i.e. what special properties do they have? Are they commercially available? Where?

Nobody asked this before, but you are right, those bricks are different. This kitchen range is built with what the participants of the workshop could bring in. Those were the only available bricks which were large enough to span the black oven. Those are not stone but man made and used in accumulating industrial ovens. I forgot the name of it, sorry but it could well be magnetite. Because of this material the heater is hard to get going, all the heat is gobbled up by these bricks. But when warm, it will stay hot nearly forever. The only time I've used these and I won't do it again if I can avoid it.

Peter Peterson wrote:In one of your posts at Permies you say: “... a round ceramic fibre tube one. The bricks are there only to fix this tube in place.” Can you tell me (us) a little more about this tube? Where to buy it? I am in Germany this days.

This is made from ceramic fibre, the same stuff as superwool. The tube is made using vacuum with an added binder and is used in industrial processes such as steel melting. It is highly heat resistant, insulating and very little mass, ideal for a heat riser. Try googling "ceramic fibre tube", I've heard of one supplier in Belgium but there should be suppliers all over the world.

Those "magnetite" (or whatever they are) bricks may not be good for the firebox or any other part of the combustion core, but they would be excellent for the thermal storage mass. They would hold a lot of heat in a concentrated area.

Thanks for the answers!

Yes, I supposed this was magnetite. Actually I thought you used it at that place because of its good thermal conductivity. This would make sense, except the two bricks near the door. But ok, you say and I believe you, the disadvantage because of the high thermal capacity is more important.

I found a ceramic fibre tube even on ebay.

regards
Peter

Peter van den Berg wrote:Funny isn't it? I've made the drawings a couple of years ago and the guys who were filming the workshop found it worthwhile to picture the layer by layer method. Every now and then this video and/or the pictures in it are passing by, leaving me grinning like a Cheshire cat...

It's pleasing to hear this brought a smile to your face, Peter. It should. You've provided a very valuable and informative source for anyone lost or wandering through the planning stages! (like I was)
Once these were gathered and supplemented with your "dimensions" spreadsheet, the rest became much easier. The video of a semi-permanent "in-home build" was comforting - seeing an RMH build that had obviously taken into consideration the concerns of a safe, lasting, indoor build.

My vote would be for this to become "must see" in the "where to start" category

Peter van den Berg wrote:
This is made from ceramic fibre, the same stuff as superwool. The tube is made using vacuum with an added binder and is used in industrial processes such as steel melting. It is highly heat resistant, insulating and very little mass, ideal for a heat riser. Try googling "ceramic fibre tube", I've heard of one supplier in Belgium but there should be suppliers all over the world.

High Peter,
I happen to be Belgian and am trying to source a good ceramic fibre tube
Any chance you would remember the name of that Belgian supplier? (or any European supplier for that matter)
Thanks for any info!

Hi Frere Daran,
The ones I had from Belgium are bought from Joris Pouls, who's building his own version of batch boxes nowadays. He's the one who started to use those superwool risers some years ago. See his website.

Peter van den Berg wrote:Hi Frere Daran,
The ones I had from Belgium are bought from Joris Pouls, who's building his own version of batch boxes nowadays. He's the one who started to use those superwool risers some years ago. See his website.

Wauw, excellent info, thank you much Peter!
___
I'm finally gearing up, with two possible places to build my first rms, 'will be in spring probably