How To Make A J-Tube Cobb Rocket Stove

I make a cobb (clay, sand & straw) rocket stove with some salvaged firebricks. This is my first J-tube rocket stove and I'm excited to learn how it works. Thanks for watching.
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[@chefboyrdanbh]

The 4x4 card board trick is genius!

[@cecilarchie4112]

Good job, thanks Mr. Greenshortz.

[@GreenShortzDIY]

Thanks for watching Cecil.

[@marshallmarshall78]

Great job! I really enjoy learning from your videos. Thank you very much!

[@GreenShortzDIY]

Thank you for the complement. Thank you for watching.

[@cgseicc]

Me encantó tu vídeo amigo, una excelente idea para aprovechar toda la biomasa de los arboles.

[@ajaymehta685]

Perfect 👍👌

[@FredMcIntyre]

Nicely done Tom! 😃👍🏻👊🏻

[@GreenShortzDIY]

Thanks as always, my friend. Have a nice weekend.

[@michaelkrepel3182]

Sorry for the late comment. I couldn’t watch the whole video. It kept crashing right as you completed the front of the feed chamber. I was happy to see that you finally built a j-tube, but bummed that I couldn’t watch the whole thing. I will try again next week when my signal should be better. Have fun with that j-tube. I bet you won’t go back to the simple rockets now that you have tried it.

[@angs8068]

Use the cardboard from the toilet paper rolls and fill it with lint from the dryer add wax so they burn longer. Actually i soaked the lint in the melted wax then filled the rolls and my husband’s friend loved them when they were trying to start a fire at their favorite hunting ground.

[@therespectedlex9794]

Sounds good but even before I click on your very plain logo, I can bet you don’t have your own channel.

[@angs8068]

@@therespectedlex9794 nope. Don’t want one. I just learn from KZbin and pass it on.

[@libbiemorin2555]

well done project! If you do not want to use a lime or linseed sealer: For my cob bench and oven I mixed clay/sand to a slip consistency/added a small amount of white sauce(yes, white flour and water cooked on the stove) and mixed well: applied about 1/4 in:/ took a plastic disk (yoghurt lid cut flat) and used it to burnish the surface. The action creates a bonding of the clay and acts as a water seal.

[@therespectedlex9794]

Sounds like salt dough without the salt. Salt might be a good idea to preserve it?

[@TheRojo387]

Knead it into the cob and get a VERY plastic earthen mixture.

[@everythingandanything-xr1ls]

well done Tom, great job BGW hello from ireland

[@GreenShortzDIY]

Thank you for watching! :-)

[@allenchase3987]

I was thinking just have the base front brick permanent and that would still make it possible to do the initial feeding of fuel

[@GreenShortzDIY]

Thank you for the tip. Thank you for watching.

[@epiphgd4302]

You mightn’t be able to clean it out easily though.

[@TheRojo387]

​@@epiphgd4302 That's what a sloping burn tunnel might be for. The ashes roll out due to gravity.

[@lucadelmare5542]

fantastic… hello from Italy

[@GreenShortzDIY]

Thanks for watching, Luca. Apprezzo il tuo incoraggiamento.

[@ohneehe123]

good one

[@GreenShortzDIY]

Thank you for watching.

[@paulorobertofeichasfeichas1595]

very good job. congratulations.

[@GreenShortzDIY]

Thank you for watching.

[@davidpadilla2571]

Exelelente 👏👏👍 estufa

[@thereseserbo4834]

what's up greenshortz happy new year

[@gonnahitcharide]

You’re doing the hard work for me as I gear up to build my own shortly. Thank you for the great tutorial as always! I do get a kick out of your announcements that “the train is here” as the train horn is blowing, as if it could be anything else, though some may believe you if you say that the Georgia Wooly Mammoth roams free near your location. 😉 ✌🏻

[@TheRojo387]

The less volume in the riser's walls, the faster it heats up, and the faster its burn speed picks up.

[@epiphgd4302]

Love it. Any follow up vids on it?

[@senolt8448]

merhaba,my garden is filled with rocket stove😀greetings from Turkey🤘❤️

[@GreenShortzDIY]

Merhaba! Thank you, my friend.

[@sspence65]

the front air feed is not necessary, that's the purpose of the shorter vertical of the j tube. cob the whole front vertical tube in. build your fire in the bottom of the front vertical, not the horizontal fire tube. you could push a couple of balls of paper down the horizontal before building your fire to kick start the draft.

[@mariedinger2382]

Would you be able to use a rocket stove for indoor heating?

[@GreenShortzDIY]

You can heat indoors with what is called a rocket mass heater. It uses an enclosed rocket stove with ductwork that carries the exhaust through a mass (usually cob or pebbles). The mass absorbs the heat and radiates it into the room slowly. Lots of good videos about it. I haven’t made one yet. (Saw your GreenShortz icon…thank you for your sponsorship.)

[@mariedinger2382]

Thanks. I am very interested in your channel and would love to get some feedback on some future projects I will be making on my own journey on being more green. 😀

[@GinaKayLandis]

This is really cool. I always wonder how to recreate without red Georgia clay! lol! Will some standoffs be added to the chimney top before it dries completely? Great idea, too, to cover the 2 x 4 with cardboard.

[@GreenShortzDIY]

Hi Gina. Thank you. :-) I think you can find clay in powder form at the local home supply store. I do plan to add standoffs to this rocket before it dries. I've got two of the three still in my old cobb stove. I'll find a third and add them in the morning. It's only a day-and-a-half dry, and it was wet to start, so it should be fine. The cardboard worked like a charm. I didn't expect it to be that easy. Thanks for your support.

[@GinaKayLandis]

There is a pottery studio local to me, I will ask if there is a brand or type of clay available there as well! Thanks fir the suggestion of the clay powder!

[@michaelstansell1001]

@@GinaKayLandis Another option might be the cheapest clumping cat litter you find (hopefully unscented) because it is usually just bentonite clay. This option may be much less costly than clay from pottery stores.

[@ESLinsider]

7:35 is a good idea. Wondering if a stove like this or a hybrid of your other welded j tube stove could be put in a van? Or what sort of mod's would need to be done? I like the cob or maybe adding perlite cement to the stove to add mass so it would retain heat after the fuel is gone - I hope ;-).

[@GreenShortzDIY]

Hi Ian. It might be interesting to combine the two stoves you mentioned. A metal j-tube rocket stove with a massive cobb thermal mass around it. You could have it go through the van horizontally-firebox on one side, chimney on the other. I’d make sure you have a fresh air intake from outside the van. Don’t want to rob the interior of oxygen. Safety is still of paramount concern…any flame heat source inside anything is. Still, I think the concept could work.

[@ESLinsider]

@@GreenShortzDIY Thanks for the ideas! 2 questions... Would a layer of an inch or two of perlite and cement be lighter than the cob around the metal and still have a similar effect? Would you need to put some sort of closure on the feed of the j tube for safety or is it fine without?

[@michaelstansell1001]

@GreenShortz DIY, have you considered an inner layer of cob for the chimney with a high perlite content so it is less of a heat sink? Although not as structurally strong, it could be surrounded by traditional cob for strength. I built an L-tube around wire mesh with insulative cob made with perlite and then encased it in lime render for weatherproofing and strength. This burner has been in use for a year and although there are small cracks in the render they re-close in between uses.

[@GreenShortzDIY]

Good ideas. I think that would have benefited the efficiency of this stove. I did a bigger coil in another stove and move the shower over there. I haven’t used this little one any since then (no heat sink). I am thinking about using it to heat a floor or radiator for a tiny house project...some time in the future. :-) Thanks for the feedback. I’ll have to learn about the lime wash process. Thanks for watching.

[@TheRojo387]

It actually needs its inner surface to be a heatsink or it simply won't heat up enough to heat its internal air to draw through a heavy enough draft to sustain the burn.

[@howardnicholls5447]

Could you make the double

[@dianefink1978]

👍😀

[@therespectedlex9794]

How long do you have to burn it to ‘bake’ the cob solid?

[@GreenShortzDIY]

I'm not exactly sure, Lex. I don't think this first burn was a full bake. My guess would be 4-5 times as long. It depends some much on how much moisture is in the cob. However, I think it would have been better for me to let this dry for a couple of weeks before firing it. I can never wait though. :-) Thanks for watching.

[@TheRojo387]

​@@GreenShortzDIY Here are two suggestions: first, if the burn tunnel slants upwards to the chimney, then the air that combusts will tend more to want to go that way, to "rise". Second, charcoal shards and beads add insulation to your cob, due to microscopic pores full of air. When hot enough these shards combust and form pure gas, adding even more insulation.

[@baraemanuel8469]

Cobul amestecat cu 40% nisip rezistă la temperatura in timp ?

[@reneebrown5598]

Yes. But shouldn't you keep your j tube at an angle so the front is lower than the back? Wouldn't that make it easier to self feed?

[@GreenShortzDIY]

Hi Renee. I'm not sure. I've just started experimenting with a rocket stove with a J-Tube. I need to play with it some more. What have you heard? Thanks for the feedback.

[@reneebrown5598]

@@GreenShortzDIY from what I've seen myself and in videos the self feeding works better if the feed tube is angled at about a 10 o'clock angle. Sorry I always sucked at geometry. Lol. But split the difference of straight up an sideways. I think its a 37° angle but don't quote me. It feeds better and doesn't need to be fiddled with to fall into the fire area as it burns down. Try turning your top brick of the feed tube to angle. That should do it. Other than that I love your build

[@GreenShortzDIY]

Thanks for the suggestions. I always get great tips and ideas from the community here. I think the cobb is still soft enough to shave, I’ll make some tweaks. Thanks for watching.

[@karthiyzos3887]

15:30 is really original ?

[@jasonbroom7147]

I really like this build, but I have found that pavers and modern bricks are simply too porous to work for the burn chamber...that needs to be all fire-brick to last very long. I will also mention that any air gaps in the feed area or burn chamber will really hurt the performance, so seal those as well as you can. Don't make the feed area any more than 1/3 the height of the riser...or it will compete for the role of "riser". Big thumbs up!

[@GreenShortzDIY]

Thanks for the feedback, Jason. I appreciate knowing your experience with pavers and bricks, versus firebrick. I have experimented with both, but haven’t burned them enough to see any issues. I have too many rocket stoves, so none of them get regular use. Thanks for watching and for the thumbs up.

[@jasonbroom7147]

As you tighten up the design to be more efficient, the burn gets much hotter, which will decrease the time it takes for pavers or common bricks to fail. If you cook anything on it, you'll see it will grill much better and boil water a lot faster. It is very interesting to look at your "rocket stove row", as it is like a living history of the evolution of how they are built. Very cool stuff!

[@jasonbroom7147]

@@ocpd23 Old style bricks are fine, but the newer ones are not dense enough. They will crack and fail under the extreme heat of a rocket stove.

[@makingmemorieswithmichigan1368]

Do I understand that your last name is Mills? My Uncle Warren moved to Georgia from the Upper Peninsula of Michigan Wondering if we R related 🤔

[@GreenShortzDIY]

Yes. My Mills roots are from Middletown, OH. That’s a little closer to the UP. By the way. I spent some time in college in Porcupine Mountain State Park on Lake Superior. It’s a beautiful part of the country. Thank you for watching.

[@gonnahitcharide]

Hope you’re ok, Tom. It’s been a while since you published a vid.

[@GreenShortzDIY]

Yeah bro. Doing fine. Got a longer project in the works, plus some client projects that have taken extra time. Thanks for checking in. I appreciate it. :-)

[@TheRojo387]

Any clay will do.

[@bsiever007]

Video is still glitchy.

[@GreenShortzDIY]

I see it now, but on my phone. Are you watching on a phone? The other viewer I heard from, who had the same issue was able to scroll past the “bad” spot and watch the rest. I’m guessing it’s a KZbin server issue, my export file plays fine. I will look into it with them. Thanks for letting me know. Thanks for watching.

[@bsiever007]

I am using my iPad over wifi. Unfortunately the video terminates after the glitch and is not viewable afterwards. In most cases it is recommended that the video be removed and a clean upload be done.

[@bsiever007]

I was able to view the rest of the video by doing what the other viewer did.

[@GreenShortzDIY]

Hi Willameena. Thank you for helping me with this problem. KZbin is going to re-process the video for me. They said it would take 24-48 hours. I’ll let you know when it is done. If you are willing to test again, that would be amazing. Thanks again.

[@bsiever007]

I would be more then happy to.

[@bsiever007]

Video got corrupted. Started to glitch at using clay bricks.

[@GreenShortzDIY]

Someone else said that too. I’ll take a look. Thanks for the heads up.

[@GreenShortzDIY]

Initially I wasn’t seeing the problem (on my desktop), but see it on my phone. Are you watching on a phone? Another user was able to scroll past that spot and watch the rest.

[@jwfinkler388]

Error message just as you were adding front bricks. “Something went wrong. Tap to retry.” Does not working. Will attempt viewing again, later.

[@GreenShortzDIY]

Thanks for watching, JW. Hope it works on your next go round. I feel like I’ve seen the message before, but not on my own videos.

[@jwfinkler388]

GreenShortz DIY great video, I forced it past the “bump” to enjoy the remainder. What will you be doing for a pot stand-off? Gas stove grate or ... carry on and stay safe.

[@thereseserbo4834]

i see you are barefooted are you earthing?