Mass heater into a truck, 47kg gas bottle?

Hi all

have spent all summer researching and reading up on rocket stoves, cant get my head round the numbers but i think i have the practice side down!
I am Currently living in the back of an ex removals truck, on an industrial site so having a standard smoke stack is a no no, and i would like to keep the mass to a minimum if any at all

what i have built so far:

47kg gas bottle

3X3 "J" tube but my feed tube is 22 degress outward

3X3 Riser wrapped in ceramic header wrap rated to 1200c

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rough shape of "J" tube

space between the top of the riser and the inside of the gas bottle is about 20mm

i have got a 6" solid flue pipe down the bottom of the bottle then attached a flexible flue to the end


my problem.....

when its windy i get a backdraft no matter how i position the flue, i have tried to fabricate cones, a spaced bucket on the top nothing seems to be stopping it the wind and the cold temp are making it really cold in the truck, average of 4 degrees before i fall asleep. im not in a great financial situation (hence the truck)

any help will be greatly appreciated! and if your nearby Somerset Taunton i will quite happily exchange labour! (im a mechanic if it helps)

I'm guessing you are likely on a very limited budget like me. What type of material is the J-tube made from? Lengths of feed,burn/riser? Is all but the feed tube inside the tank? A 3" system is very hard to get to work except for just a little rocket stove. Sounds like a 100 pound tank. Is the tank about 14x46"?
Here's a few ideas.
You need to match the J-tube size to the exhaust duct. Preferably go to a 6" J which the tank would easily support, or as a least desirable option a 3-4" exhaust. Your draw is being slowed way down by the larger exhaust, and the large space between the riser and the inside of the tank. Although it's a 3" riser your top gap is maybe a bit small. The burn tube needs a lot of insulation. In a pinch you could use sand or better yet cob, and riser needs more insulation as well. An 8-10" duct pipe around it lightly packed with fiberglass insulation could work.
Having the exhaust go out the side wall (Even a dryer vent outlet might work) on the down wind (leeward) side of truck could also help.
Without mass you have to keep a fire going all the time to maintain any temp unless you well insulate the interior space. If you could use any kind of mass maybe a barrel or 2 of water would be better than anything. Getting the water heated is a bit of an issue to keep it simple and SAFE!
These are a few off the wall ideas to give you a place to start.

John Adamz wrote:I'm guessing you are likely on a very limited budget like me. What type of material is the J-tube made from? Lengths of feed,burn/riser? Is all but the feed tube inside the tank? A 3" system is very hard to get to work except for just a little rocket stove. Sounds like a 100 pound tank. Is the tank about 14x46"?
Here's a few ideas.
You need to match the J-tube size to the exhaust duct. Preferably go to a 6" J which the tank would easily support, or as a least desirable option a 3-4" exhaust. Your draw is being slowed way down by the larger exhaust, and the large space between the riser and the inside of the tank. Although it's a 3" riser your top gap is maybe a bit small. The burn tube needs a lot of insulation. In a pinch you could use sand or better yet cob, and riser needs more insulation as well. An 8-10" duct pipe around it lightly packed with fiberglass insulation could work.
Having the exhaust go out the side wall (Even a dryer vent outlet might work) on the down wind (leeward) side of truck could also help.
Without mass you have to keep a fire going all the time to maintain any temp unless you well insulate the interior space. If you could use any kind of mass maybe a barrel or 2 of water would be better than anything. Getting the water heated is a bit of an issue to keep it simple and SAFE!
These are a few off the wall ideas to give you a place to start.

Hi John thanks for the reply.

its made from mild steel, when just used as a barely insulated rocket stove the hottest it was getting inside was 400 degrees, after reading up on all the issues of using mild steel and high heat im wondering how long this will last if i insulate it and get high temps, i have done about 20 test burns while building it trying to keep that rockety bit going and there is no issue yet

will get some measurements later on and try and post a picture

i read somewhere that the flexible exhaust causes drag thats why i went for the bigger size flexy : and the 3" is already welded to my bottle quite extensively might try and source a reducerfor the far end of the flexy.... do you think that might work?

i have got a load of cavity insulation, just trying to find something to pop round it that will fit inside thats not to big! oh and yes it a 100lb bottle pretty much

the bottle does retain some heat for a good hour or so i have had some long wood sticking down into it and left it for a good hour before coming back and still burning really well

again thanks for the advice, last question how do you work out the gap from the riser to barrel?

ok so measurements

gas bottle is 14 inches diameter, 48 inches high
riser is just under 31 inches 3X3 Box section mild steel (now with an 8 inch dia pipe around it ready for insulation (trying to find some)
feed tube is 22 degrees and\9.5 inches long
the cleanout (under feed tube) is 14 inches long the feed tube starts about 5 inches in toward the gas bottle so the burn tube is quite short?
the flue is a 6 inch sat at the bottom pointing opposite the feed tube


can anyone give me a rough idea how big my gap should be for the riser?