I was hopping some other regulars would chip in but …..
The roaring noise associated with the rocket stoves name sake, happens due to the strong draw being pulled through the fire box and burn chamber.
So when the stove is on song, you will get the roaring effect, the higher the temperature the more likely to hear the roar.
In order for this to work well, we need an open and free flowing route for the flames and then the hot gasses to travel through.
So the more complex the route, the more bends and right angles you install the more restrictive the route becomes.
That is why a bypass works so well because it offers a more direct route while the system heats up the chimney and warms up too assist the draw.
In your case you have a quite difficult route for the hot gasses to travel through.
To aid its travel, we need to get the very best out of the fire that is burning in the fire box and burn tunnel. We want that area to be very hot so the gasses can really shoot up the riser without any restriction and allow the hottest part of the system, that will be at the base of the riser, to do its job.
Your thick dense bricks will take some time to saturate with heat but, more importantly we need to keep that heat from passing through the bricks, that is why the insulation is so important.
Different folk have different ideas but in my own builds I use a lot of insulation, I think you will get much better overall performance with 2” of insulation rather than 1” but in any case, the whole fire box, burn tunnel and especially the base of the riser will benefit good insulation.
In order to keep the flow going we need to keep the route as clutter free and open as possible, (piped systems are really quite an old designs compared with the much more free flowing ‘bell’ designs) so the first big restriction in the gap at the top of the riser.
There is not really an upper limit as even four feet above would work well but we need a bare minimum of 80mm. Personally I would go for 100mm as a minimum.
The gases have to spread out and travel down, while at the same time shed off heat that radiates out of the barrel, this area needs to be free flowing and not restrictive.
Next the gasses need to travel through the pipe, if the pipe is covered in mass and sealed completely, the the gasses will keep going and slowly heat the mass. If the mass is not sealed the heat will dissipate like the radiating barrel.
Ultimately the gasses reach the vertical chimney where they can successfully rise, further helping by pulling the gasses through the sytem.
The end of the burn chamber and the base of the riser will be the hottest part of the system so insulation is very important at the point.
In summery it is really difficult to trouble shoot from an arm chair so we must rely on your input but hopefully some points made will help you work out some improvements.
I also notice you are burning quite large pieces of
wood, small dry
kindling will heat the stove up much faster, I control the heat largely by the size and type of wood I use
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