Martin White

Thanks everyone for all the Input. Going to spend a week or 2 not thinking about it and then start dismantling the main bell. Would a rebuild to walker's design as below be suitable for retaining the bench? New door in order and going to go out and buy bricks this time, I feel it will be much easier to get it air tight, the uneven granite was quite difficult to work with.
I'm a joiner I should have bought drawings I know better.

Yes it goes horizontal from the bench out the wall, then a 90 degree elbow. Had wanted to avoid a flue inside, added to the catalogue of errors!

photos of course
It's randomly on Wikipedia also.
It's called Wartle Station.
Great house, lots to do as ever with old houses.

I had played with the idea of cutting a small hatch in the top of the bench to accommodate a small cast iron door for pre warming the flue. Will look at doing this. I bought the flue thinking I could add a metre at a time until it reaches the desired draw if you see what I mean.
Seems I need to take the core out. Build the walls up higher and re evaluate. The flue connects to the bench on the far right hand side at the same height as the inlet to the bench. Both are just slightly higher than the firebox but it's marginal. Both inlet and out of the bench are at the highest point I could fit them in the bench, just under the bench seat.
I have around 500 pieces of granite left. Being in the NE of Scotland the stuff if everywhere. My house is a Victorian train station so stone is all over the place. I had planned on lime plastering the whole thing to hide my shoddy stone work I'm possibly just fed up of looking at it as it's been problematic (of my own making).
Thanks so far everyone for the input. Really helping.

Internal main chamber is 800mm x 800 mm 1m high. I got myself confused with the whole sidewinder cook stove design I think and got lost along the way in some in between build that achieves not a lot. Unless the fan is running. Thanks again for your input

It is a bell type bench, 10 inches wide 12 inches deep and the flue is 6 inch twin wall insulated flue, exits horizontally then makes a 90 to vertical. Hypothetically could a brick bell be added above the riser a smaller version of the granite box but made of clay brick? Then allowing the riser to be extended. More than likely a sledgehammer job but just exploring options.

Firebox and riser are built out of firebrick with ceramic fibre wool as the insulation material. Thanks for the reply.

The answer I expected, if you were a guessing man what would you suggest to be the main issues? I realise this is difficult to answer. I really thought I was working within the bounds of the design, 26 inch riser, 6 inch cross sectional system. Nothing under 6 inches throughout.
My guess was the shape of the batch box itself is the foundation of the issue.
Looking like tearing it down is likely.
Gutted to say the least.
Thanks.

Attempting to build my 6 inch batch box system. Teething problems a plenty. Been a serious learning curve. From outset I think I took on too much information as the build progressed from different sources and kept taking little bits of information from here and there and not sticking to a definite plan that was tried and tested. Lesson learnt.  I will attach photos.
Not drawing very well for a start. Attached an inline fan I had lying round to the chimney stack as short term problem solver. Turned my stove into a blast furnace.
Issue that resulted is my square 5mm steel plate on the top to seal the small hole left from my top construction, (which is made of angle steel, vermiculite brick and cob) the steel warped and resulted in gaps all around the steel plate opening up. Could see the flames coming out the riser. Keeping the fan on stopped the smoke coming out in the wrong place but not ideal.
With the fan on and disregarding the steel issue the system warms up but the second I turn the fan off I'm getting smoke coming back out the door I am thinking this is an issue with the shape of my firebox, low and wide but who knows at this point.
I should have bought red bricks as they aren't that expensive and would've made the whole process easier and more reliably air tight, however had lots of granite lying around in the garden so thought I would use that. Not being a mason and my build essentially being dictated by the size of the granite blocks it's ended up as a wide squat looking thing which I am also wondering if this is affecting performance.
Insulation around the firebox and around the riser.
Just wondering is it a lost cause, top off and figure out another method of sealing the top. Being quite wide I found this a puzzle. Anyway any help or advice met with serious gratitude, I'm pulling my hair out. Should've fitted a wood burner!

Not yet just a few bits of kindling. The wind blowing across the horizontal opening was blowing air back down the bench intermittently. My 90 degree and vertical section of flue arriving this week. Hopefully running at full chap will help it draw also. Playing with cutting a small hole towards the end of the bench for pre warming the flue

The door and thus the burn chamber were due to compromise, it was the only door I could get hold of at the time, not an ideal situation but have allowed enough space to the lintel incase I need to change it. Burn chamber is turned on its side to facilitate the door shape. I am aware this might not work and may need changing sadly. Chimney is to the right of the bench. Twin wall flue runs out horizontally from the end of the bench then makes a 90 degree to vertical.