cob bench without ducting

So I was thinking about rocket stoves today. I want to pose a Question.

Obviously you need fire brick to make the feed tube. Then you use a metal tube for the burn tunnel. You have that connect to a 90 degree elbow and shoot straight up into the barrel. The gas flows up the tube and down the sides of the barrel exiting at the exhaust flew located at bottom and going into the ducting that imagine is going into your nice nice heat battery aka your couch made out of awesome cob.

But.

What if you made mudd bricks with an archway that has a half circumference of 12 and half inches. Then you could take these sun-dried mudd bricks and place them where needed. One brick on then another brick upside-down and repeat until you have 30 feet tunnel from your bricks. Then you can seal them with mudd and cover them with cob. That way you won't have to use as much metal.

Feedback?

blyskawica Hatfield wrote:So I was thinking about rocket stoves today. I want to pose a Question.

Obviously you need fire brick to make the feed tube. Then you use a metal tube for the burn tunnel. You have that connect to a 90 degree elbow and shoot straight up into the barrel. The gas flows up the tube and down the sides of the barrel exiting at the exhaust flew located at bottom and going into the ducting that imagine is going into your nice nice heat battery aka your couch made out of awesome cob.

But.

What if you made mudd bricks with an archway that has a half circumference of 12 and half inches. Then you could take these sun-dried mudd bricks and place them where needed. One brick on then another brick upside-down and repeat until you have 30 feet tunnel from your bricks. Then you can seal them with mudd and cover them with cob. That way you won't have to use as much metal.

Feedback?

Yup, all the heated benches on masonry stoves are done that way.... Anytime bricks (special shaped or not) are used, sealing becomes a problem. Most of the masonry heaters are double skin for this reason (It is also required by code in most places... though not in Russia). It is one of the reasons masonry heaters cost so much.... and a big part of the reason the RMH uses pipe. Pipe is cheap (check the price of ceramic flue if you think otherwise) and easy to seal... this gives skin one and the cob is skin two. The pipe acts as both a form for making the cob arch "in place" as well as sealing the flue path. Both ways work though.

In my case my whole flue path is metal... feed included, with the sole exception of the top of my bench... which is upside down to what you describe... but a metal trough with cement over it. I finished cutting the holes for the bench intake and exhaust today. When next I work on it I will weld in my intake support and even up the top. Then I can assemble it outside to test before moving the whole works inside.

Would you be able to use two hole or round center hole concrete blocks for your exhaust tube? Well mortared into place, of course to keep the exhaust from leaking into the room, of course. The blocks would add more mass while directing the flow through a baffled system.

I need more concrete blocks at the farm anyway, so when I get my firebrick I'll add a few dozen of them to the order. When we do trial run on a rocket stove in the courtyard I'll give it a dry fit to see what the worst case scenario might be.

Lolly K wrote:Would you be able to use two hole or round center hole concrete blocks for your exhaust tube? Well mortared into place, of course to keep the exhaust from leaking into the room, of course. The blocks would add more mass while directing the flow through a baffled system.

I need more concrete blocks at the farm anyway, so when I get my firebrick I'll add a few dozen of them to the order. When we do trial run on a rocket stove in the courtyard I'll give it a dry fit to see what the worst case scenario might be.

I saw a picture of someones set up that was done that way... unfortunately, I did not hear of the outcome when/if it was finished.

no no metal tube for the burn tunnel. yes bricks for the burn tunnel and feed tube; preferably bricks for the heat riser (space dependent). metal tube for the exhaust is normally used but terra-cotta, mud brick, stone, fired brick, cast cement pipe Etc. all work. the cob is several inches thick to prevent gas seepage. it takes a large crack to allow exhaust to enter a room. this is why we have everyone do test bricks of the cob mix they want to use for the bench and stove surround. a good cob mix wont crack deeply and you wont have a leak problem.

your brick arches should work well. as long as they are sealed up well.

Lolly Knowles wrote:Would you be able to use two hole or round center hole concrete blocks for your exhaust tube? Well mortared into place, of course to keep the exhaust from leaking into the room, of course. The blocks would add more mass while directing the flow through a baffled system.

I need more concrete blocks at the farm anyway, so when I get my firebrick I'll add a few dozen of them to the order. When we do trial run on a rocket stove in the courtyard I'll give it a dry fit to see what the worst case scenario might be.

yep it works you will want a slight incline the whole way. remember to put in clean-outs. the only place to watch is the first 5 feet of the exhaust. it runs about 500 degrees in this area and can get hotter. depending on the cement mix you might be able to burn out the lime. This wont be a problem if you have a thick layer of cob over this part but this is also where you need to put your first clean-out. just keep an eye on it it wont effect the stove but it will be a touch nasty to clean out cause you may very well get some quick lime. wear gloves when you clean out the stove and you wont have to worry about it.