Looking for judgement on rocket heater

Hey guys, new here but gathered alot of useful stuff in the forums on rocket heaters.. and now i want to build one.
I want to cover my rocket stove with a barrel so that I can use an exhaust to vent fumes from a small space. I cannot fit in any thermal mass on the exhaust, it is purely for ventilation.

Space is so limited in fact that I want the whole thing to be very compact and hence I was thinking that instead of the barrel covering the whole stove, it could cover just the top of the vertical pipe which protrudes from the insulated section. This would mean that two barrels of the same width could stack one on top of each other...
Im guessing that this is sounding problematic but hopefully my rough picture may make it easier to see my point..

Bare in mind that it is not to accurate scale but is a guide of the sort of proportions i was thinking of. Also when i say barrels, im more likely thinking two number 10 food cans or something fairly similar.

So anyone want to get started on the numerous things that are probably wrong with this?

Thanks in advance.
Theo

I can grock your jist....

What it looks like you are proposing is an "L-tube" rocket heater with just a heat exchange and no mass. You should insulate the heat riser inside the top barrel. This will help you get a more complete burn.
Problem is though, if this is constructed on a #10 can-scale, made with actual #10 cans, then you're gonna burn out the top can just using it for a heat source. It would make a great 'hot-plate' for a more controlled cooking surface than a typical #10 can rocket stove. However, I do think your idea could be scaled up to something like two 7.5 gal steel barrels (17"h x 14"dia.) with a 4" system. Maybe you could squeeze it down into two 5 gal barrels, but the steel on the 7.5 gal size a thicker gauge.

Great... sound positive. I had already thought that the heat riser should be insulated (at least a little) all the way up, and yeah i was hoping it would make a nice little stove for boiling water and veg.

Can I just check that when you say "burn out" the top can, you do mean literally burn right through it?!?
Also I'll probably be using a full J pipe eventually as I like the vertical feed.

Should be knocking it together soon so will post relevant info and pics when I do
Cheers for your help

yeah, burn through... not right away, but it won't last more than a couple dozen burns

Hi Theo. What Chris B said, and... you're not providing a big enough 'manifold'. That's the area out the back of the upper barrel where all the flue gas needs to rush out. Because the gas is coming in from all angles inside your top barrel (as it should for an even heat), the gas needs a gentler transition to being alined in one direction, and then flowing out the rear pipe. You will have more success with a manifold roughly three times larger than your intake, just to round out the corner that the flue gas needs to take. A final outfall the same size as your intake is fine.

Theo : I have a friend we'll call him Dr. Smith, who cooks both of the two meals he allows himself daily using a Cast Iron 3" sewer street ell for a rocket stove.*
Actually he does this in good weather on his side porch, and is probably back indoors using a 80 yr old wood cook stove he made 'rockety' !

His is the Smallest Rocket Stove i know of that gets daily use better than 6 months out of the year !

If you are able to do better than that, you have come to the right place, g'LUCK !

I have read and re-read your message, and I don't get it,You are using this rocket stove as a powered exhaust to '' vent fumes from a small area" ?
OR - you want to be able to run an exhaust and your rocket stove both at the same time ?

A much shorter barrel 'B' , and shortened to match Heat Riser might help with the restrictions at barrel 'B's exhaust , but thats just off of the top of my head which is still spinning from the riddle you posed !
Again , g'LUCK , Pyro - maticly yours Allen L.


* Why yes, I've had lunch with Dr. Smith !