Fox James

Have you done any revision about the internal temperatures inside your bell?
Apart from the very top 8-12”  you might not need to worry about  expansion or high temperature cement.
In any case you can use the standard pizza oven cement mix called ‘home brew’
3 Parts Silica Sand
1 Part Portland Cement
1 Part Fire Clay (powdered)
1 Part Hydrated Lime
This is cheap, very easy to use and good for 4-500c

Hi Mark, what a great project and it sounds like you are having fun already?

I just read your opening post and wonder about your logic regarding your one year old verses a J tube!
Firstly I will just say that I really like J tube’s designs, they make a lot of sense for many applications, relatively simple to build and very easy to use.
However the open top fire box will be an irresistible draw any child of any age and a perfect hight too!
Something like shorty batch box design can be set quite high off the ground and also have a door.
Secondly I would advise reading up on the use of any high temperature matting or wool, its use is very popular on this forum but as an example, if you use it inside your bell and you get a down draft of wind (very common with open top J tubes) you could be allowing your room to be contaminated with potentially toxic dust.
Of course that is totally up to your discretion as the product  is very effective but does come with some risk!
Your ideas about building an internal brick chimney is unusual but sound….. and should be very long lasting, the down sides might be the work and cost involved or maybe the fact that you just can’t check to see if it has cracks or leaks but that would also apply to  any internal chimney. Something like a cast iron pipe or stainless steel pipe might be an option.
You may want to look at cement board and find out what is available near to you. I often use high temp cement board for chimney construction. That would be long lasting and simple to use.
Vermiculite board would kill two birds with one stone as it is very insulating and also very easy to work with.
Good luck in any case……

I have this short video showing a slightly different lay out, it looks awesome but is a a bit sensitive.

Hi and welcome to the forum.
There is a good reason why you are finding it difficult to find info on such an endeavor!
 There are a few issues to overcome and very few people actually succeed to successfully reach this goal.
To start with the very nature and design of a rocket stove is to burn hot and fast for short amounts of time in order to store gentle heat is a dense mass.
Where as most cooking situations require a consistent but adjustable heat source, and that is not easy to achieve with a rocket stove.
This sort of project will be quite a big undertaking and very unlikely to be cheap!
At the very best you will end up with a compromising oven, certainly compared to a clean easy to use, fully temperature adjustable, gas or electric over anyway.
However when there is a will there is a way……
Incorporating a hot plate is probably the easy way, you can quite easily and for a reasonable cost, build a dedicated 6” J tube rocket stove with a large hot plate.
You have to be a bit more careful  not to loose to much heat through the hot plate if you want to further heat a mass and heating a half decent oven with a door is going to be a challenge.
I guess the next step is for you to tell us more about what you would like and expect. The area you want to heat and the actual space you have?

Yes 500 + at peak burns depending on what you are burning and how diligent you are at feeding the fire.
Every stove will perform slightly differently (some times very differently) it is a compromise of how much wood you cram in and how much air is being pulled through the system.
No doubt you will soon discover what is best for your particular circumstances..

Hi Mark, If I recall rightly you are thinking about building a 6” J tube?
If so then you may possibly see 500c exiting the top of the riser but a more average temperature would 300-375c.
Given perfect conditions, a well insulated straight up and tall chimney, 1” square lengths of softwood in the fire box with no ash build up, then maybe 500c for a short time.
A 6” batch box is more likely to offer 900c at peak burn.
There is a good reason for the big temperature difference, a J tube burns the tips of the fuel in a six inch square box, a batch box burns a whole load (batch) of wood right down the whole length in a much bigger box!

Hi, I think silicone is an option for you, in general there are a few silicone options namely, high modulus, low modulus and high heat.
Although none of these are suitable for anywhere in a flame path, they will stick tiles to an outer surface.
Low modulus is rated somewhere around 150c it remains very flexible. High modulus is rated up to 250c and is a great choice. High temp is rated to 300c, personally I don’t like it much as it is not as adhesive as the others and twice the price!

However there are other options for adhering tiles in the form of purpose high heat tile adhesive!
This comes in various forms, I like the tube variety (just like a silicone tube) and is often rated to over 1000c but it won’t be at all flexible at that rating, so you might want the 300c tile adhesive as that allows a tiny bit of movement but sticks very well indeed.
My local store can offer about 20 choices of high heat tile adhesive…..

Rico, yes I have lots of YouTube videos and my designs are also documented on this forum, I don’t like to keep re posting the videos but you can find them on my channel https://youtu.be/LbZTkuiMBRU

Hi Rocky, batchbox stoves are more complex than a J tube, they would generally require, accurate air control and a door, this makes them more time consuming and more expensive to build.
Many folk prefer the bigger load and the more powerful results that a batch box can offer. however you can still use them with half a load if you don’t need too much heat.
On that basis I don’t think anybody has ever asked your question before.

You can often find people comparing a 6” batchbox with an 8” J tube in the power stakes but they still work in a slightly different way.
Personly i have both designs in use in different locasions . I prefer a J tube with a hotplate for cooking and a batch design for mass heating.
Good luck with your revision, keep it up and you will discover the best option for your personal use.

Well it is a small world, I bet you are glad you left that horrible place…should have moved to Guernsey   ha ha!

We have rocket mass heaters and there are rocket stoves without the mass.
Therefore we could have a compromise between the two.

A six inch J tube can be built from lighter materials like vermiculite board or insulating fire brick but it is the mass that can cause the structural issues.
If you want long overnight heating from a pre heated dense mass then there are not many compromises but if you want fast radiant heat then you just need the rocket engine.

I have my own version J tube with a small amount of mass that works perfectly for my circumstances, it has glass viewing windows a short burn tunnel and a spinning vortex riser.
I also use an extremely efficient vortex stove with no mass at all but it looks amazing and throws out heat like you would never believe but has zero mass!
Peters latest Shorty core is relatively easy to build and is much more forgiving about re loading to produce radiants heat all day long.
A lot depends on how well your house is insulated and how much wood you have to burn?