Rocket mass Heater latest questions.

Hello all, I've been on this journey for quite some time and I have done a lot of research and read through the books but there is still some things I can't figure out or maybe I missed.
Im surrounding my heat exhange and firebox with the proper clearances of insulating/non insulating cob then incased it a red clay brick wall all the way around on a already exsisting concrete foundation. Do I just mortar the bricks to the floor with regular mortar or would it be better to combine them with cob? Previously I used cinder blocks and then removed them because I felt clay bricks would be better heat exhangers. The cinder blocks were mortared down and came up very easily from the foundation with a mallet...some weren't even stuck very well.

I would use regular mortar for setting the exterior brick shell. The heat exposure should not be high enough to damage it. I think you were right about the poor heat transmission of common (hollow) cinder block. Solid concrete blocks would probably work fine for an exterior shell, though if esthetics matter, that would be a reason to avoid or cover them...

Okay thank you! Also do you know if I can make a right turn about a 1-2ft after the manifild exit??

Sure you can put elbows anywhere in the duct run; the sharper they are, the more restriction they make for flow.

I saw from your pictures that your bricks have hollow cores - those will also insulate somewhat. It would be best if you filled the cores with mortar on the faces exposed to the room (insulation near walls is a good thing).

So leave the ones close to the wall empty? That wont cause any cracking issues?
I get what your saying and it makes perfect sense. Ive been struggling back in forth with this build for two years haha its just such a confined space with little options but I think I have a good idea on the layout. Il update pictures soon.

The bricks you have are probably hard and would be brittle in high heat situations, but the heat level as the shell of the thermal mass will not be enough to stress them.