Rocket mass heaters

Hello,hope this finds y'all in good health.
I think i read where the bell can be the mass, and if so,how does that work?
Also,in my part of west virginia, we have yellow clay,which does not appear to be very useful for this particular application.
Any advice on this would be greatly appreciated.
Thank you in advance ☺
Rich Coole.

Hey Rich,

I moved your question to the Rocket Mass Heaters forum.  They are about the nicest, most helpful folks on the planet, so give them a minute to chime in.

Welcome to Permies!

Hi Rich,
basically there are two types of popular systems in the RMH world, the piped bench and the bell. The piped bench uses ductwork to run the RMH exhaust through high mass which sucks up the heat and releases it into the space. A bell system works differently in that you have a much larger open cavity that the exhaust pools in and stratifies with the hot gases on top and the cooler gases below. This system can be ideal for spaces where a large mass bench is not possible. A bell can allow you to build vertically with a thin shell that will release heat more rapidly than a mass bench. Check out https://permies.com/t/102393/Horizontal-bench-vertical-bell for more discussion on this topic.

To add to Daniel's summary, a bell can be thin for quicker heating, or thick for massive storage and long release time, or even a combination of thick walls and a steel access panel to give some instant heat plus long storage. A bell can also be low and wide like a bench if that suits your space. (You do need some taller spot to house the heat riser; it can be a steel barrel or a masonry box/cylinder as desired.)

Thank y'all, I appreciate any and all input,lol
I know y'all use clay, our is either yellow or white, and to date,I've not heard of a good use for it. Maybe that's why there's so much of it,🤣🤣🤣🤣🤣
I'll probably have to go with the mortar and perlite.  

Why do you think your clay is no good? What happens if you try to make a "snake" from it and bend it? What is it like if you make a brick shape from it and dry it (especially with some straw, hay or grass clippings mixed in)?

I've tried a couple bricks from both. By themselves, when dried,don't hold together very well, but I've not tried grasses or other fibers. I will make a couple this week, and hopefully let you know how it works out.
No one I've known has done this,hence the reason.
If it were a good material, I would like to think it would've been used more.
This is going to be a fun adventure.

Again, thank y'all so much for all the help.
Honestly appreciate it!!!

Rich Cool wrote:I've tried a couple bricks from both. By themselves, when dried,don't hold together very well, but I've not tried grasses or other fibers. I will make a couple this week, and hopefully let you know how it works out.  

Might help if you describe the ratios and types of sand in your cob mix, and the process of determining the purity of the clay source.  My creek clay has a variable amount of sand aggregate already in it, and occasionally silt that I have to eliminate before use.

Never mixed it, lol. I'm kinda new to cob, just been around furnace cement mix all my life. It comes in a tub, just add water,lol.
I'm looking forward to trying this, turns out our clay is usable,so Saturday just got booked 🤣🤣🤣
I'll try one to one, the two clay one sand. With tall grasses I have around.
Yup,going to be interesting.

You generally want something like two or three sand to one clay for cob. If your clay already has some sand, that would affect your mix ratio. Wild clay needs to be thoroughly kneaded before it becomes good cob; straight from the ground it tends to break up easily.


Grass can make decent cob, but stems rather than leaves are better (hay or best of all straw), and it is better if dried before use. Dry grass/straw will absorb some water after mixing into cob, so the material can start sloppy and easy to mold, and stiffen a bit in a half hour so it doesn't sag too much after placement. Broad leaves are bad for cob, as they make planes where there is no clay contact. Pine needles are too weak to work well.

Well i dug some up,just a shovel full, and tried it. With two handfuls of sand, fairly coarse sand, it had all the characteristics of everything I've learned. So,I made a teeny tiny burn chamber. Now I'm waiting for it to dry. Results to come. 😀😀😀

Glad to hear your clay is working. Don't be discouraged if your tiny burn chamber doesn't work very well, scale matters when it comes to fire and a small J-tube 4" diameter or less can be very tricky and will not get nearly as hot as a common 6" or 8" system. 6" and up work reliably as long as you follow the standard guidelines.

Thank you everyone  for the help and encouragement.  I am truly grateful!!!