Wood stove as a Batch Rocket Firebox?

Firstly, greetings from the UK and I'd like to thank all involved in this fabulous forum for all their help and information - brilliant!

I've been studying Peters excellent Batchrocket Resource site and would like to build a Peterberg inspired rocketstove to heat a masonry bell and a hot water system.

I want to use an existing 'box stove' (Charnwood Country 4) as the firebox and connect this to a 130mm diameter lightweight, insulated heat riser.. The internal firebox dimensions of the box stove are approx 350mm wide, 355mm high (sloping to 235mm high) and 210mm deep. According to the stove calculation table by Doug Ptacek the ideal firebox size for a 130mm system is 187mm wide x 281mm high x 374mm deep. There's obviously some discrepancies between my box stove firebox dimensions and the 'ideal'... The main issue appears to be the depth (front to back) dimension. I intend to use the Matt Walker floor based secondary air channel in this application. I don't think there's room for a sidewinder type of port/riser arrangement.

I'd like to use the box stove as part of the construction as it has a nice, close fitting glass fronted door and precise primary and pre-heated secondary/air wash controls. I'm quite prepared to cut away part of the back wall of the stove to accomodate the preferred front to back dimensions of the batch rocket firebox and modify the baffle arrangement. I intend to line all of the firebox with insulating vermiculite firebricks and hard fire bricks backed by ceramic fibre blanket in high abrasion areas.

Do I really need to make major alterations to the box stove or would the finished contraption work (albeit with perhaps a certain compromise on performance) with the existing dimensions? Could I simply place the fuel load at right angles to the port rather than the recommended 'front to back'?I realise that at the very least I would need to cut out the 'port' area in the rear wall of the stove to connect this to the heat riser.

Anyway, many thanks in advance for any help and advice and there's a barrage of extra questions to come!

John, welcome to the boards.

What you are trying to do is fraught with problems. Size matters in this case, your firebox is completely the wrong shape. The air inlets in the door aren't probably the right size and placement isn't almost certainly wrong. You need to protect the inside of the firebox, otherwise it will be eaten away when insulation is around it. And, even when you are able to protect the walls and ceiling, what do you want to do with the port itself in the back? This will become one of the hottest areas of the whole thing, so eventually the port will get wider and wider.
Of course, you can do what you want but I would think you'd better start from scratch, using the right materials for the job and building the layout which is known to work. Do a rough mockup in the backyard and run that, you'll get an idea how violently this thing will burn. When you build another shape or use other materials you're in unchartered territory.

Thanks for your welcome and swift reply Peter. I suspected I may be looking at this from the wrong angle...

What I may explore is simply to use the door and frame from the box stove and construct the firebox to your design from firebrick. My metalworking skills are fairly poor and this is why I'm keen to use the nicely engineered door of the stove. The combined box stove primary and secondary air control openings closely match the recommended sizes on the spreadsheets and I like the option of 'fine tuning' the air supply to optimise the burn. The finished heater is for use in a living room in our house so I want the whole unit to look quite nice in addition to performing well.

As the spinwheel air control on the door front lines up well with where a floor based secondary air tube would sit, would it be OK to simply use your standard firebox design with the tube on the floor rather than the roof mounted P channel?

Many thanks again for your help Peter.