John Harrison

Mark, I would say yes Have a removeable lid.  The ability to easily check if there are any issues with your system is well worth it.

I have a J tube in my workshop which drives a masonry/steel bell. The 'lid' is a cast iron section that relies on gravity to hold it in place. I have a fibre gasket which provides a basic seal and it works well. The only downside is that it is a very heavy thing to lift off to allow inspection/cleaning.

In my Batch Box rocket firebox I've used board similar to this stuff (it's widely available in Europe)
Vermiculite board

In my experience it works well but does abrade after a while even when loading fuel carefully. I've also used it in several woodstoves as firebox lining and baffles and it does wear after prolonged exposure to high heat. It really needs to be treated as a consumable part.

Incidentally, My BB firebox uses the insulating board for the walls and ceiling and I use firebrick splits for the floor (backed up with superwool insulation). The splits cope fairly well with the logs being loaded into the firebox - they survive longer in that application than the insulating board.

As your mason says, the preferred option would be to use a high temperature/high alumina/Fondu cement mixed with the perlite. It can be hard to get hold of and is fairly expensive stuff - over here in the UK anyway...

If you can't get hold of high temperature cement I'd use a mix of clay and 'normal' cement (OPC). If the 'normal' cement gets overheated it can crumble and fail but the clay should still hold things together.

I've used the front, door and sides of a small woodstove and have successfully built a 'sidewinder'batch box space heater that also heats water.

I followed Peters dimensions very closely and it works well. To create the correct firebox size and geometry I used a thin steel frame lined inside with a combination of hard fireclay and lightweight insulating firebricks.

Mark - for my BB rocket brick bell I used a cast iron oven door as an inspection door on the front. The added benefit is that it starts to radiate heat almost as soon as the fire is lit.

I also incorporated an old Georgian cast iron oven (with door) into the bell structure which also radiates heat quickly as well.

Glenn's right. You need to have a very hot, highly insulated firebox/riser to burn the wood cleanly first and then target the heat generated towards your heat exchanger.

Any cooling of the combustion area will result in a dirty burn that will smoke like crazy and deposit tar and creosote.

I'm using a conventional 'wrap around' wood stove boiler as a heat exchanger on top of a 5" BB rocket riser to help heat my hot water and provide central heating. The boiler is rated at 45,000 btu/hr and this output, it appears, can be achieved if you keep the firebox well stoked with decent dry hardwood mixed with a little softwood.

The BB also heats a single skin brick bell.

When I get the chance, I'll post details of my build and how the system performs.

If the firebox was left uninsulated the high temperatures needed to help promote clean combustion would be hard to achieve.

Additionally, the firebox (if made from steel) would degrade very quickly under the prolonged exposure to high heat. There are quite a few threads on the forums showing catastrophic failure of metal components in rocket stoves.

Here's a photo upload test - fingers crossed...

Ah right - thanks Thomas.

I thought I would have to link to some photo sharing site or similar on the web. When I return to base I'll give it a go

Thanks again.