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Rocket Stove prototype - 1 (polytunnel/greenhouse heater)


Ok folks this is a small experiment just to test the rocket stove theory and do a small dry run prototype with 1 stage.
If this works out I’ll do a larger 2 stage one and hopefully when I get a larger polytunnel I can install it as a heater for next winter.

Its a very good way of producing heat very quicky whilst using all the small bits of wood n twigs that noone needs.

Ok so let me take you through what its about…..

I am going to have a go first with tin cans as they are cheap. Also got some bigger ones as well. Got a couple of nice big veg oil ones from the chip shop but will use those for the 2nd stage bigger one. So for this one will use a medium size one there for the outer shell.
Just a HEALTH n SAFETY word of CAUTION before we begin. Be VERY careful and I mean VERY careful, cus if you do have one of those Fray Bentos pies in a tin, whatever you do, DONT undercook it ; ). In fact I would recommend dont even buy one ok. Its says 20-30mins which means at least 45mins

And your are also going to need some insulation, like ash or sand or perlite or vermiculite.
I think this will cover it ; )

Ok now we will need some tools, metal clippers for a lovely nice even smooth cut…oops : /

Ok so what we are trying to do is create an L-shape.
I have a small normal soup can there going into two slightly larger tins (economy new tatoes 17p)

now the larger outer shell. Ok this time I used a small drill and drilled holes in a circle then just snipped the gaps in between. Looks better

Leaving a bit of space for the flue to sit on. It goes within the shell.

Now add the insulator on the bottom and sides. I have also cut a hole in a lid piece to secure the vermiculite on the top.

See nice n neat. DONT make it air tight as air will expand and needs gaps to escape.

So lets get some small sticks and start a fire

So the heat rises up the flue and sucks in the air at the bottom

and as we get up some heat, as you can see the wood is burning well but the flame and oxygen are being sucked in

and as she burns along to the end of the can as you can see shes sucking in nicely. There was a bit of smoke at first as any paper labels on the cans burn off.

and now lets make her a bit bigger by extending the flue and the inlet cans. This will mean more drag and so we can move the fire along more and put longer twigs in

So another fire

and pack em in and watch it working

SO here’s the deal, the reason we are doing this. This L-shape is actually creating a kind of vortex. You see in a normal wood burner you burn only a fraction of the burnable gasses with lots of nitrogen, carbon dioxide and monoxide escaping straight up. It not the wood that burns, its the gasses in it, which expand to about 10x the area of the wood. SO as these gases come out and expand, with the super heated (insulated) L-shape they all burn. Therefore no smoke or gases coming out the top and hence a very efficient way of burning and producing heat.
See that vortex go

and as the heat stays in the L of the chamber you can have the fire quite a ways from it with the flame and gasses and air being sucked in to be burnt fully

See how nice n hot that is

Ok how about a twig feeder (copyright STT ; )

ah yes works after a fashion (NB notice I am in the polycave NOT gassing myself) and all the flame and any smoke is being pulled down to be burnt clean.

And so there we are. Thats the theory.
Next stop a 2 stage version. This is where you have a shell over the top of the flue (heating it as a hot plate) and a exit flue out of that. The stove then acts as a pump effectively pulling air in and pushing out the flue.

Ok so if you wanna have a go do it OUTDOORS in the fresh air and do it safely.
Its amazing how hot the thing gets, hence the need for good insulation (NB incandescing tin cans can ignite other things close by) so be careful and insulate properly.

If you search on youtube you can find many examples. Also look up Rocket MASS stoves that use a longer exit flue for heating.

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Excellent idea and build Stt. Might try this myself.

8 Mar, 2013


nice one StheT ! always interesting to see what results you get from home-spun DIY projects.

8 Mar, 2013


A very sound idea, but too much for me to do, it's a man thing lol

8 Mar, 2013


Frightens me. That tin will melt eventually.

9 Mar, 2013


Garden is great thing, but polytunnel is evidently your passion. So you fell in a burning ring of fire? Lol.

9 Mar, 2013


That vortex of fire is amazing! Great job Stevie! Certainly very tempting to have a go, chiminea stoves could do with adapting that principle?

Be great to have the kettle on the top ready for a brew or maybe a frying pan ?

9 Mar, 2013


I will ask something totally different what money are you paying for that size Vermiculite the cheapest I can find is £14.00 a total rip off.

9 Mar, 2013


Boys and their toys came to mine, great idea though, but not for me, I think you have done a great job, just a bit scared that the tins will do a melt down and set fire to the wooden bench and burn the whole lot down. lol. or you will be taken into hospital with carbon monoxide poisoning. lol :O) you look as if you thoroughly enjoyed making that. Well done!

9 Mar, 2013


Bampy, just wait for version 2, gonna be a whole lot more professional,

DB,OO, ST, well yes I think if the fire chamber were a bit bigger with more burnable area then it might get up to a hotter melting temp but would just collapse. A proper one would use a steal L chamber.
I did do it outside and due to the vermiculite the outer time was not to hot to the touch. So the bench under it was fine. Most of the heat is shooting out the top hence if used as a stove you could have boiling water in 5mins.

Yes ST the theory is all about the vortex. When it was going good I stuck my nose over the flue, no smoke, no fumes, no dangerous Co2 or monoxide.

What i would say is that this set up burns quite quick so you need to keep feeding it every 5mins hence better designed ones have a vertical feed and better still would use long bricketts.

9 Mar, 2013


Bjs, yes I sympathise, it would seem very overpriced considering how light it is!!

Around here I think I saw 10L bag for about £5 with 20Litre bag at about £8.50 . So this 100L bag was about £26 or £28 one of those so i though what the heck.
I need something for my seeds/cuttings so it'll all be used.
Vermiculite n Perlite was the same prices

If you found 100litre bag for £14 I'd go for it

9 Mar, 2013


Just found a guy who seems to know his temperatures so the materials to finally use are an important question

For a short warm up I think my cans will be ok for the final version and some sort of warming mass for the flue should hold that longer. But I might just use it for a warm up any way. I think actually my little prototype here would not it seem be burning all the Co or Co2 so outside flue exit is essential (anyway)

Heres a nice example of a home rocket mass heater
and a good permirculture website

9 Mar, 2013


What is permiculture, Steve?

9 Mar, 2013


in the second clip does the stove heat all that seat going round the corner of the room?

9 Mar, 2013


Never heard about permiculture....

9 Mar, 2013


this is from wikipedia

'Permaculture is a branch of ecological design, ecological engineering, and environmental design which develops sustainable architecture and self-maintained horticultural systems modeled from natural ecosystems'

hope that helps kat

9 Mar, 2013


Thank you Sticki. Why do you always add Q or A after mine? Hmm?

9 Mar, 2013


no idea kat! coincidence that we are both on at the same time?

just happened to wonder when i looked at stevie's second link to a clip

9 Mar, 2013


Lol. Too many coincidences!
I wonder, if Steve find the question now.

9 Mar, 2013


i will try very hard not to ask a question after you have kat????

9 Mar, 2013


Kat, ''Permaculture is a branch of ecological design, ecological engineering, and environmental design which develops sustainable architecture and self-maintained horticultural systems modeled from natural ecosystems''

9 Mar, 2013


; )

9 Mar, 2013


Yes Sticki, the exit flue carries the heat and the mass holds it so you have one big radiator plus the 2nd stage hob which gets very hot when burning wood

9 Mar, 2013



have you been watching kevin mcclouds man made home, its fascinating! tonight he made a reclining chair out of reclaimed bits of metal and a deer skin then they made a loo and the gas from it heated the stove!!!!

9 Mar, 2013


p.s. thats a very good quote you used stevie ~ seems to explain it very well!!!

9 Mar, 2013


You know Stevie, most of Filipino is using that kind of cooking stove but its not like what you made , here they only need a very fine wood and they only need a Big Can and drilled a hole ,and that's all , you are very intelligent you have an excellent idea:-)))

10 Mar, 2013


It might be a better idea for everyone to display their own safe successful overnight greenhouse heaters ?

10 Mar, 2013


Just for everybody´s safety.

10 Mar, 2013


I bet you meant that blond planted heating system, Dianebulley?

10 Mar, 2013


Good link Kat, I found that first link I put up with the chap talking about temperatures needed very informative.

Seems you need very high temps to burn absolutely clean and he seems to recommend firebrick. However it would need alot of feeding to get up to that sort of temp.
So seems any design will carry some risk. I know open fires and normal stoves emit dangers so with an open fire its very important to sit up wind/breeze of it. However this design is intended to burn 'better' and yes as Junna points out usually for the purpose of cooking.

For my next prototype I'll be doing a 2 stage one.
I quite like the design of this 2 stage one with a nice firebox feeder.
I like the way he has a slot to start the fire off and its used just to heat his shed up. I like the way he then switches to recycled wood brickettes

well hey I got a debate going : )

10 Mar, 2013


Blue Peter, eat your hearts out!
Awaiting the next blog with bated breath.

16 Mar, 2013


Just found this Stevie, Reckon you could do some toast or a baked spud on that contraption Stevie, eating al fresco and all that!
Typical thing a 'boy' would experiment with, me thinks, brilliant. Lol.

7 Apr, 2013


stay tuned, have all the bits for the next one : )

7 Apr, 2013


On a bigger scale next time? Will it light up the skies over wales?

7 Apr, 2013


well a certain other task has preoccupied me this weekend but will be building another bench area suitable for the Rocket 2 : )

8 Apr, 2013


Is the certain other task nearly done now?

8 Apr, 2013


the certain other task is indeed finished for now this very morning..see blog

8 Apr, 2013


It's a great job!

8 Apr, 2013

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