Can I build my "bench" vertically in a RMH ?

Just wondering if its possible to build my "Bench" vertically in a J tube style RMH. Basically the pipe would come out of the manifold and up, then hit two 90 bends, come back down then up again to the chimney. The pipe would follon an "N" pattern thru a vertical mass.I would respect the lenght/number of turns laid out in the RMH book the only difference is the bench.

My other option was again a vertical mass but the pipe for the "bench" part zig zags up the vertical mass in a series of 45 degree rises eventuslly reaching the chimney.

I want to do this because I want to keep the RMH where the old woodstove is a a vench would just not fit in the space.

Thanks for your input !

HI Joel;  Welcome to Permies!
The short answer is Yes ! You can go vertical instead of horizontal.
However... there is another option.  In place of vertical piping,you could build a large brick bell!  Its easier and looks good as well!
Either design RMH (J tube or batch) can be plumbed into a bell rather than horizontal piping.  And the amount of cob you would need is drastically reduced!

Let us know what your thinking, we are happy to help. We have a whole crew of happy rocket scientists eagerly awaiting your questions!

Welcome to the wonderful world of rocket science!  Your lab coat might show up in the mail later... but until then carry on!

Thanks for the reply Thomas ! Ive heard a bit about bells but didnt know they could be used on J-tubes.  

-Does the entire bell need to be firebricks ?

-wouldnt having less thermal mass give me less heat retention ? I want to be as efficient per square foot of RMHf space since my house is only 750 sq ft which is why i want yo go vertical. No room for bench but I have two open lofts upstairs on either side and the RMH would be between these.

Where can I find information on size, proportions to follow ? I dont really understand bells because from my understanding you really need the same cross sectional area everywhere in a RMH and bells font seem to follow that.

Thanks a lot

Hey Joel;  Yes , bells can be used with a J tube.  Although you more commonly you hear about them with a batch box.
Regular red clay bricks are used in a bell.  Only at the core would you want firebrick.
And really what you might like is ceramic fiber boards and ceramic fiber blanket. They are the newest thing to use in RMH construction.
The blanket is used in the riser and is known as a five minute riser (how long it takes to build one). HIGHLY recommended using one!

No loss of mass with a bell. You can place stacks of brick inside the bell, as well as the bell construction itself, to create mass.
In your house a ceiling fan might be a good idea to keep that heat moving.

Rmh construction particularly in the core is an exact size.  Piping length is a known parameter and so is bell size.

Here is another site you can check out, it is run by our friend Kirk Mobert (Donkey) You will find bell dimensions there, as well as a bunch of technical information. )http://donkey32.proboards.com/
Here is another site that specializes in batch box construction ) http://batchrocket.eu/

Here is a post all about 5 minute risers )https://permies.com/t/95849/Working-Morgan-Superwool-ceramic-blanket
And here is a long one about my Jtube into a brick bell.)https://permies.com/t/99519/Baby-Dragon-Roars
And another)https://permies.com/t/94980/Brick-Bell-Shop-Heater

Greetings Joel,   As Thomas suggested, bells are a good option for what your looking for as bells are designed to stratify the heat and I would say do it better when there is more vertical height vs horizontal. If you go to the batchrocket.eu site, it does give bell sizing for the system your building but remember, these numbers are based on a batch rocket, not for a J tube. I don't know the equivalent but would say that the volume would be smaller since J tubes don't put out as many btu's.
Just as an example, here's a video showing a system that uses a ducting system similar to what your describing. (Probably not the easiest thing to clean without taking it apart):

Hi Joel;
Here is a post specifically about bell size.  This post is at Donkey pro board, here is a link to that      donkey32.proboards.com  
And here is the thread  http://donkey32.proboards.com/thread/1822/sizes-single-bell-systems.

These numbers are for a batch box.  6" can use a bell with 53.8'  ISA  ( internal surface area)
a 7"  can use a 77'
an 8" can use a 95.3'
ISA in a bell is measured by the four walls and the roof.
The floor does not count. And if ceramic board is used as a roof then the roof would not count either.

As Gerry mentioned, J tube output is less than a batch box.  
When I built the 8" J tube in a bell in my shop.  
It was suggested that I stay with 6" isa requirements.
I think I went slightly oversize, with closer to 65' isa and I have had no problems.

Thanks for all the information Thomas and gerry much appreciated.

The 5 minute riser looks awesome.

So from what I understand, you can form your burn tunnel and feed chamber with ceramic board. Do you screw these together to hold them in plsce temporarily or stick them together with refractory mortar then build around that with red bricks to hold it and support it together ?

How did you connect your riser made with the pipe and morgan superwool plus (on their website i think they  its superwool extra now ? )blanket together to the burn tunnel so its secure


Did you get your ceramic fibre board from morgan as well ? Wondering if theirs any type to avoid like the wool blanket


Also, doing rough math then I substract 23 (the difference betweeen 8 and 6 inch system ISA) to get my 4 inch isa for my 6inch j tube i could go with a bell of around 30' ISA. I think mine should have a pretty good draft as my chimney is nearly 25 foot tall and indoors

Ill keep reading, and found 55 gallons barrels near me to pick up. This will be my big summer project but im trying to.figure everything out now.

Thanks again !

https://www.amazon.ca/ceramafiber-Ceramic-Fiber-Blanket-Insulation/dp/B01HLM8PII/ref=mp_s_a_1_1_sspa?keywords=ceramic+blanket&qid=1582284094&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUFUV0lRMzQwVzg4NzEmZW5jcnlwdGVkSWQ9QTAzMzY1MDEzNzRNV1lGQzlXRUhTJmVuY3J5cHRlZEFkSWQ9QTA3MzU5NDYxODg2SFhRMUlQUjdHJndpZGdldE5hbWU9c3BfcGhvbmVfc2VhcmNoX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=

What do you think of this product ?

Hi Joel;  Welcome back!
Well there is no hope for you now!
You have contracted the deadly RMH virus.  
The only cure is to build your own RMH AND after that, to keep it in remission , you must tell any and all strangers all about rmh's and how super awesome they are!
Congratulation's ! You are taking the first steps to becoming a full fledged rocket scientist! Continue to wear your jeans and tee shirt until your lab coat arrives...


Now lets see about answering your questions.
Yes ceramic boards for the burn tunnel and split firebrick for the feed tube.  I did notice some difference in ceramic boards , but not like the difference between blankets.
I carefully wrapped my burn tunnel with foil to help hold it together. Then surrounded it with clay bricks. Use no metal screws.
When I build another, I plan on making a thin plywood form to go inside the burn tunnel (will burn out with the first firing) This will keep your tunnel the correct size while building , as I found out on mine. Without a form, it is hard to keep a uniform size in your core as you stack brick around it. I had to disassemble part of mine to correct that problem.
The riser simply sits on top of the core, I did bracket it with bricks at the bottom and then stuffed C.F. blanket to seal it up.
A close look at my shop heater build post will show you how I did things.  

Now about barrels. As you see, I used one on my shop stove to get the instant radiant heat. My shop is uninsulated. If this was in an insulated house I would have gone with an all brick bell instead.  No need for rapid heat in a warm building.  
The ceramic blanket has successfully sealed masonry and metal. A lot of folks told me it wouldn't. So it can be done if you like.
Your bell can be built with refractory mortar if you can afford it or assemble with fireclay and sand.   The big difference, is clay mortar will pop free if banged to hard. Good news, is it reconstitutes with water and you can reuse it.  Refractory mortar is forever... Oh and a #50 sack of fire clay is $7-20 a sack of refractory is $50-100...  I used clay!

About the CF blanket you located on amazon.  Might be fine , I don't know as it is not morgan super wool.
To start #8 is overkill, #6 blanket works great.  I wouldn't think you will need 25' . I bought 12.5' and it gave me enough for two risers and plenty of extra to use on my bell build.

It is so exciting to build your first rmh!  Might I recommend building  a temp core out in your yard , just to experience it. Really gives confidence when your doing your real indoor core!
And ... you won't have to wait for summer.  If you try this be SURE to use clay to stack your core, dry stacking has many air leaks and your rocket won't blast off .

EDIT)   I would aim for 45' ISA Joel, 30 just seems to small.     I'll also toss out that 8" J tube is easier to work with.   More room to load and longer burn times.

This is the space im working with. I dont really know if the house is "well insulated" its strawbale but it seems drafty and I do have the issue with the heat rising. I do have a ceiling fan but plan on installing a more powerful one. Ive been fixing up the house slowly and fixing some of the worst draft spots and thats help a lot already.  

Yesterday it was -13F (-25C) and I was gone all day and only left a space heater on when I got home at night it was close to 50F or 10C in the house. It took a couple hours to warm it back up to the high 60s but again upstairs during the.peak heat must of got around 75. The wood stove can heat up the place nicely but it just feels so inneficient. I can be sitting in front of it with the door closed and barely feel any heat. The pipe radiates an ok amount but I feel like most of the heat just gets sucked up. Its got a super strong draft with that tall chimney. I was sorta worried the barrel would make the upstairs way to hot so a brick bell could be something to consider.  Plus weve had a very mild winter compared to the norm and ive used 2.5 cords already but I only burn if its quite cold. Next winter my girlfriend will move in and I imagine ill have to keep the place a bit warmer lol


The house is 24 feet by 24 with slab and ive got two big 5x5 facing south. In the morning the heat from the sun on those two windows is awesome even on a cold day ( 0F or -6c). Im hoping a 6 inch system is powerful enough to heat the place. I already have the chimney in place and wouldnt have to buy new pipes plus out here 8' pipe is just hard to find. I found one store that could order some for me but it was ceszy expensive.

That is a really good idea with the plywood box ill make sure to go over your build thread again I must of missed that part !

Hi Joel;   I see why you want to stay with 6". Here's a new thought.  Other than going thru the roof where you would want a Class A pipe.
All the indoor pipe can be thin wall hvac pipe!  
Here at home Depot , a 5' long stick of 8" hvac  is around $10
On my shop build I used two sticks of 8" black "regular" stove pipe down low, just to avoid dents from careless people (Me) walking by.
And , more good news , I assume you already have a 6" class A thru the roof,?  
With 25' of warm indoor chimney , you can go up indoors with 8" hvac and just reduce to 6"  to go outside!

Several builders have successfully done so.
Food for thought!

Joel;  Its 41.5' ISA difference between 6" and 8"  not 23'

I second the recommendation to go with an 8" J-tube system and reduce to your 6" existing chimney. I have a 7 1/2" J-tube RMH  which currently connects to a temporary 6" chimney out the wall and up, only 12' from fuel feed to top of chimney, and it drafts excellently. I believe you will have no problem.

A bell system can be less massive than a ducted mass, but does not need to be. Figure the volume of material in your bell walls, and you can find out how thick they need to be for a desired total mass. You probably don't want thicker than 8" or 9" - it takes heat a long time to get through that much mass. Also, corners will function better if they are quite rounded; the 4" radius corners on my 9" thick bell walls never feel warm to the touch unless it is cold out and I have fired for hours.

If your system is oversized for your house, you will just have to burn less frequently.

I believe you could build a hollow brick bell to just fit in the stair well with the stove pipe on the inside of the bell just as it is now. A batch box burn chamber or even the stove you have would be just toward the stairs from where it is now with the riser going up beside the stove pipe.  The stove pipe then draws the cooled gases from the bottom of the bell.  The expert Peter van den Berg in this post Rocket Mass heater Event explains  In order to alleviate the low draw I also did the same trick here as with the Minnie: made a vertical slit of 4"x 1/4" just below the lid, this upped the stack temp just enough to ensure the proper functioning of the core. If You click on his name in the above post you can send him one of our infamous Purple Mooseages and ask him to check if this is correct.