RMH keeping the heat close by

In the photo i hope you can see the idea is to force the hot gasses down and around the base of the heat riser, the idea is to incorporate two blocks so the gasses will be forced down, then up then down again, thus warming the exterior wall of bricks before exiting in to the manifold. The heat riser will be insulated to the base leaving about an 1" gap for the gasses to move through the channel, does anyone have any thoughts if this would work. Respect Antz

Yes, it would work. But there's no need to let the gases go up and down twice, one time will do the trick. Change in the direction of the gases pose friction so you'd better to do that sparingly.
I think what you mean by a gap of 1" is the top gap, the opening between the end of the riser and the top of that brick "barrel"?
The right way to do this is to replace the barrel by a completely brick surrounding, preferably quite a bit larger than the barrel itself. The bricks will extract the heat slower so you need more surface area to do the same. In fact, when it's large enough this will act as a masonry bell heater, the combustion core being a rocket heater in this case.

About the top gap: unless you want to cook on the top, you can make that actually as large as is practical. Years ago, I tried to find the maximum distance between the riser and the top in an entirely brick setup. The ceiling of my workshop limited the top gap to 4 ft and the thing kept working without any sign of hesitation. One remark though: this experiment was coupled to an adequate chimney. Without that, it wouldn't work but that goes for most of the rocket heaters I've worked with of whatever construction.
See this link for the brick experiments.

Hi and thank you for your interest, I will, as you suggest, channel the gasses only once. As for the bell i am restricted to a 60cm footprint, I have only 25m sq. to heat.
The 2.5 cm gap was referring to the space between the heat riser when insulated (if needed?) and the bell walls, not as you thought the "top gap". Your thought on this are most appreciated.
Kind regards Antz

OK, so your footprint is 60 x 60 cm, to heat a space of 25 m2. What is the insulation of that tiny home, what size of system you are planning for and is it an inhabiited space or just a workshop or office? Also, what is the height limit of the heater and do you want quick heat or not?

The 25 mm gap around the riser isn't enough to let the thing act as a bell, it will be more like a contraflow system. This would work as well but I'd expect the produced heat is more than you could extract and stock this way. About the riser insulation: try to find calcium silicate firebricks, the light ones, those would be insulative enough without additional superwool or the like.

Thank you again for this assistance. To get things clear i live in an old east German circus wagon, that i have rebuilt myself, it is insulated with 60mm hemp throughout, a double skin of pine 40mm out side and 20mm skin of pine inside. The floor is 80mm of borox coated paper fluff with 30mm floorboards, the wagon is rated for 16tons and for the past four years the space has been comfortable helding up to the common -10 C. winter months here. I have been using an old Wamsler cooking range a bit like an AGA or Rayburn (no back boiler). The fact is that i wish to improve on the high emissions and fuel consumption. Having built many rocket stoves for outside kitchens i thought i would try out a rocket style design self build, good for confidence and to live by example. Well yes i do have a stove builder friend where i can get Ca-Si in most sizes. I have the current stove concept placed on a slab of Ca-Si. As for the max. foot print it could go as far as 70x150x120(W,L,H). the height of the wagon is 180 slanting up to 220, thus the riser center point would be roughly 2meters. The stove would run along the side of the wagon currently protected with glasswool in. and farmercell board to use the existing flue system, 120mm. would be nice but not necessary.
I hope that puts you in the picture. best wishes Antz