Batchrocket icw barrel and bench (as a bell)

Hi all,
After a lot of reading I decided to register since I believe I can use some advice regarding the construction of our RMH. This will be our first build ever.
At first I looked into the "classic" J tube design. The thing I don't like about this is the open feed tube. After going further down the rabbit hole, i ended up on Peter Van Den berg's batchrocket site.
I like the core that peter designed, with the floorchannel sec. air supply and square riser (150mm/ 6") (number 7: "A simpler core design" under the Design section). This design seems pretty straightforward, and I would only need to cast the cover of the core.

Combining this effective core with a barrel over the riser would give (according to my humble opinion) the best of both worlds.
In the bottom of the barrel I'd make a channel to a bench: I still haven't decided on whether to go for tubing covered with cob, or use bricks (single brick bell).

Option1: a bench as a bell: According to Peter's site, the ISA should be max 5,3m² for a 150mm riser. For a bench of 3m in length, 50cm high, and 50cm deep, I would end up with 4,5m² for the 3 long sides + 2x0,25m² for the ends, all in total 5m². I only found a picture on his website of a similar design, but with a "classic" bell. Unfortunately no plans available.

Option2: covering 150mm channels with cob.

My questions:
- do i keep a 2"/ 5cm gap between the top of the riser and the top of the barrel, just as one would do in a J design setup?
- is it correct to state that the maximum length of the channels (in option 2) is 10,5m/ 35ft?
- how does the inside look of the bench (bell): is it only the 4 wall with a cover plate, or do I have to divide it into multiple chambers? Is 50cm high enough to properly work, or is it better to build a narrower but higher bench?


Our homestead is located in South-Africa, temperatures go as low as 4°C in wintertime. There is currently no wood stove installed yet, hence the need for a solution before winter

Hi Fred;
I'll try to answer your questions.
#1)  No, a Batchbox riser requires a 12" clearance.
#2) No, 35' would be for a 6" J-Tube, 6" batch works with 8" J-Tube numbers, so 50'.
#3) A bell is open, no dividing walls.

Using a barrel will give you a large amount of instant heat.
Perhaps, it might be more than you would like.  
Your barrel can be covered up to 2/3 with cob to mitigate how much instant heat you need and how long your bell will hold it.

Hi Fred, exciting times for you then.
The old style batchbox is a powerful stove but it has a few restrictive aspects from my perspective.
The riser it’s self, is what makes the stove work so well but, it is a tall component and you would need more than one barrel to enclose it.
Another issue for some people might be the internal metal work that will deteriorate quite quickly although Tom (who made the above post) can sell you a few components that will help your build……
There are more up to date models that don’t use a full size riser but rely on a good, ideally straight up, tall chimney.

I don’t think the riser less stoves are quite as powerful but, they might offer more options to make them fit into your home.
One of the benefits from my prospective with Peter’s latest design, called the ‘shorty’ is you can re load the fire any time you like without causing any problems with smoke or reducing the stove clean burning aspect.

Now that you mention it, I didn't think about the deterioration of the barrel.
You don't happen to have a link to his "shorty" model? I don't believe I came across it.

The only thing that's holding us back to build a J type is the "fear" of having smoke inside the room at startup.
And perhaps that I'd need to make our fire wood smaller: length of our wood blocks is 30cm.

Hey Fred.
I don’t think Fox is talking about the barrel. Barrels usually last quite a long time as they quickly shed the heat that’s coming in from the riser.
Smoke back can happen with any wood fired stove. But if you prime the riser and maybe even the chimney you won’t have that problem with a standard J-tube.
A way to close off the feed tube is having a tile or something ready to be put over the feed.
So if that’s what you want to build after reading up on all of the types, go for it!

As for the length of the firewood, the last one I built had a 35cm feed tube height. That would be enough to fit 30cm wood.

Hi Fred, no as Ben points out the barrel (s) can last for years, it is the  secondary air supply feed that will degrade!

Personally I love J tubes, they are very simple to build and use, one  disadvantage is the need to keep topping up the fire box with fuel.

I have my own design J tube that has a glass door and a viewing window, it also only requires a fairly short riser that easily fits inside a single barrel.
If I were you I would spend a few days looking at the builds folk have completed on this forum, there are quite a few choices.
A lot might depend on your DIY skills or your budget.

Benjamin Dinkel wrote:Hey Fred.
As for the length of the firewood, the last one I built had a 35cm feed tube height. That would be enough to fit 30cm wood.

You don't happen to have the dimensions of that setup?
I found this one in an old topic, but was never build, and is for 40cm wood.

Edit: I noticed in the construction example of "The Rocket Mass Heater Builder's Guide" that it has a 16" (40cm) feed tube, being ideal for our situation. The bench in this setup, has the correct dimensions for the room as well.
So most likely I go for this one: easy to build but more importantly most components are easy to find.

Fox James wrote:Hi Fred, no as Ben points out the barrel (s) can last for years, it is the  secondary air supply feed that will degrade!

Personally I love J tubes, they are very simple to build and use, one  disadvantage is the need to keep topping up the fire box with fuel.

I have my own design J tube that has a glass door and a viewing window, it also only requires a fairly short riser that easily fits inside a single barrel.
If I were you I would spend a few days looking at the builds folk have completed on this forum, there are quite a few choices.
A lot might depend on your DIY skills or your budget.

Oeps, almost missed your post.
DIY skills are ok, regarding the budget: we'd rather spend something more instead of regretting it later, and having to start over.
I'll take a look at your build (and the other ones).
The only problem now: there are so many different builds/models/options, that choosing is really difficult 😀

Finally, after lots of planning, I started the build.
Firebricks are 76mm and 25mm thick (230×114mm).
Burn tunnel floor length: 60cm (23,5" or 59,69cm on plan). Calculated hight of the feed is about 38cm (40,64cm/ 16" according to plan).
So far so good.

The riser however comes out at about 119cm with 12 layers in total: plan says 48" (121,92cm).
Is this ok?
I think yes since the feed is 2cm shorter as well, which with a factor 1:3 comes at a 6cm shorter riser. So in theory, my riser should be ok with 116cm. Wanted to doublecheck with you guys before making any mistakes 😀

Hi Fred. That’s so exciting you get to start!
The minor difference shouldn’t be a problem.

Feeder complete. Riser will be finished tomorrow.
I have a stainless steel barrel, but only the one.

I'm hesitating now on what to do: build a manifold with bricks (have plenty of them) or look for another barrel (will need to find one and it's paint removed, which is also time consuming).

The only advantage I see for a 2nd barrel would be the annual cleaning: a clamp is easy to remove. With the bricks, I'd need to "destroy" the clay seal and apply new slip afterwards. Not to difficult either.

Build a small brick box "manifold" and add a cleanout door, either a stove pipe cap or a cast iron door.

Thank you for this great idea! Didn't think about this. Thought I'd need acess to the top of the riser.
What would be the most ideal position to install it?

Going with a brick manifold sounds like less trouble for your situation.
I think I also saw a video of Paul where the seal was basically made from the fly ash settling on the inside of the lip of the manifold.
Or sit the whole upside down barrel on a stove gasket connecting it to the brick?!

Does your barrel have a removable lid? If so, cut out enough of the barrel floor to fit over the riser, seal it to the manifold, and just remove the lid to inspect/clean the riser (in conjunction with the cleanout door at the base of the manifold).

Some people have removed the top of an inverted barrel leaving an inch of horizontal metal, and installed a circle of heavier steel with a gasket fitting into the recess, sometimes just held by gravity.

If you have not built your bench yet, I would advise you to make it a bell (a simple hollow brick box) rather than ducted channels. You will have much less friction, and cleaning will be simpler.

Thank you for the ideas.
Have already bought all ducting, so likely I will be using those. Thought about a brick bell, but my bricklaying is not so ... perfect, that's why I chose the ducts instead. Maybe next time for a masonry heater project 😀

When building the brick manifold, do I do it with 'regular' cement mortar?
Until now I have been using premix refractory mortar (20kg bucket): looks like clay slip to me. Was sitting under a water layer in that bucket to keep it moist. Adding water, mixing and dipping the firebricks in it went really well.
But since the regular bricks are more uneven, this might not be possible. (I might have not enough left of the refractory as well)

Hey Fred. I usually use clay sand mortar. Fine sifted clay and fine sand 1:3.

Brickwork is done.
Cutting the bricks with the diamond blade on our angle grinder gave me trouble: the aluminum in the bricks melted, making it impossible to cut them. So I started dipping them in water (5 secs is optimal to avoid double dipping), just past my crayon line.
A water saw would be ideal, but one has to improvise. Soaking the entire brick didn't work out for this refractory product as it tends to slide off.

Also prepared some samples: from 1:2 to the occasional 1:5 with both bought construction sand (orange brown color) and our own white river sand (looks like this might be to course).
Feels like 1:3 will be the sweet spot indeed.

Fred Beken wrote:The only advantage I see for a 2nd barrel would be the annual cleaning: a clamp is easy to remove. With the bricks, I'd need to "destroy" the clay seal and apply new slip afterwards. Not to difficult either.

For my RMH, I made a lip at the bottom by pressing the barrel rim into the wet clay, rotating it back and forth, and scooped it out enough that a length of fire rope sits in it. The barrel just goes on top of the fire rope and its weight holds it in place.