Rocket stove fired bath tub questions...

[klundquist]

Hi. I am new to this group and can't seem to find any threads that address the questions I have (please point me to them if they do exist).

I am building an outdoor rocket stove fired tub system with two tubs side by side. I live in a temperate rain forest that gets 35-90 inches of rain a year depending on the drought cycle. I have looked at the diagram and description in Ianto and Leslie's book and can't figure out the following:

1. How much lower in elevation does the bottom of the feed tube have to be in relation to the burn chamber...the illustration makes it look at least a foot lower.

2. In building the connecting tunnel between the feed tube and the burn chamber and the burn chamber itself, does one need to create a capillary break below these (i.e. gravel) to prevent groundwater from wicking up into the perlite/clay insulation layer and thus the connector tunnel and burn chamber?

3. Insulating the chamber with perlite/clay, what mesh size perlite does one use? Is coarser better than fine? The book says use mortar grade as opposed to agricultural grade...which tells me nothing since construction grade perlite comes in a huge range of meshes from super fine to super coarse. How thick would you make this layer?

4. The diagram shows the insulating layer covering the bottom of the burn chamber and then wrapping around to cover the outside of the lower half of the tub. How do you prevent this from disintegrating or cracking and peeling off due to moisture exposure, heat/cold cycles. Being a cob builder, I can't help but want to build a perimeter foundation for the tub, create an insulated burn chamber on the inside of that and then set the insulation layer that goes on the outside of the sides of this tub on the same foundation to protect it from wicking. Then earthen plaster the outside of this insulation layer to protect it from rain, etc. (is this overkill?). The need to protect cob is mentioned in the text of the book but nowhere in the diagram does it get used. Where does one use cob in this design?

5. I like the idea of having both burn chambers converge and use only one chimney to exhaust...though from looking at other threads (does anybody know if a dual 6" flue will work?), this may be a bad idea as the volume ratios will be off...thoughts?

6. Regardless of how many chimneys I use, what's the best way to transition from burn chamber to chimney? Can I bury stove pipe and insulate around it? This seems most stable to me as I can lock the upright exhaust pipe into the pipe that gets buried.

7. If the tub drain goes through the burn chamber as illustrated, how do you prevent the rubber seal in the drain basket from melting?

Sooooooooo many questions!!! Any thoughts or feedback would be greatly appreciated!

[Donkey]

Dec 3, 2009 15:34:06 GMT -8 klundquist said:

Hi. I am new to this group and can't seem to find any threads that address the questions I have (please point me to them if they do exist).

I am building an outdoor rocket stove fired tub system with two tubs side by side. I live in a temperate rain forest that gets 35-90 inches of rain a year depending on the drought cycle. I have looked at the diagram and description in Ianto and Leslie's book and can't figure out the following:

1. How much lower in elevation does the bottom of the feed tube have to be in relation to the burn chamber...the illustration makes it look at least a foot lower.

The difference in levels doesn't actually need to be there, and honestly, I almost always forget to include it.
It's supposed to be a pit for ash to accumulate into so you don't have to clean it as often.
Did Ianto and Leslie forget to include a measurement for that?? Heh..
Just a couple inches.. Not too deep unless you place a grate over it.

2. In building the connecting tunnel between the feed tube and the burn chamber and the burn chamber itself, does one need to create a capillary break below these (i.e. gravel) to prevent groundwater from wicking up into the perlite/clay insulation layer and thus the connector tunnel and burn chamber?

Yep. Anything made of mud or subjected to heat needs this treatment.

3. Insulating the chamber with perlite/clay, what mesh size perlite does one use? Is coarser better than fine? The book says use mortar grade as opposed to agricultural grade...which tells me nothing since construction grade perlite comes in a huge range of meshes from super fine to super coarse. How thick would you make this layer?

The coarser the better. Bigger bits will provide better insulation, though plenty of different grades in there will allow it to lock together better. Mostly I just make do with what I can find. If all you got is fines, use it.
3 or 4 inches feels good.. I've used less to good effect.

4. The diagram shows the insulating layer covering the bottom of the burn chamber and then wrapping around to cover the outside of the lower half of the tub. How do you prevent this from disintegrating or cracking and peeling off due to moisture exposure, heat/cold cycles. Being a cob builder, I can't help but want to build a perimeter foundation for the tub, create an insulated burn chamber on the inside of that and then set the insulation layer that goes on the outside of the sides of this tub on the same foundation to protect it from wicking. Then earthen plaster the outside of this insulation layer to protect it from rain, etc. (is this overkill?). The need to protect cob is mentioned in the text of the book but nowhere in the diagram does it get used. Where does one use cob in this design?

I wouldn't take the drawing too seriously if I were you.. It's more conceptual in nature.. I'd build the whole mess up on a foundation (urbanite perimeter, gravel under) surround the works in cob, etc.

5. I like the idea of having both burn chambers converge and use only one chimney to exhaust...though from looking at other threads (does anybody know if a dual 6" flue will work?), this may be a bad idea as the volume ratios will be off...thoughts?

I wouldn't use more than one exit flue.
The jury's still out on splitting flows, some have worked, some have not, some have unpredictable results. If you choose to play with splitting, I'd recombine at the end.

6. Regardless of how many chimneys I use, what's the best way to transition from burn chamber to chimney? Can I bury stove pipe and insulate around it? This seems most stable to me as I can lock the upright exhaust pipe into the pipe that gets buried.

Best way?? Which way fits your need best? Be innovative, experiment.
Why insulate the chimney? Think about where you want the heat to be dumped off at. Why not STOP insulating after it leaves that point?

7. If the tub drain goes through the burn chamber as illustrated, how do you prevent the rubber seal in the drain basket from melting?

Good point.. As I said before, conceptual...
I'd isolate the drain area from the fire. Perhaps a cob barrier.

Sooooooooo many questions!!! Any thoughts or feedback would be greatly appreciated!

[klundquist]

Thanks SO much for all of the great feedback. I'll let you know how it all works out. Cheers!