Rocket Stoves anybody ?

[Little John]

Anyone on here interested in Rocket Stove technology ?

I started one last year, but didn't get it finished before winter set in. Have just conducted the first run - absolutely bloody amazing. A few small bits of wood, and it's away ... chucking out heat like a good 'un. And zero smoke (it actually burns the smoke) once it's up to temperature.

It's still outside in a polytunnel whilst I put the finishing touches to it.

I'll post some pics - if there's any interest.

LJ

 

[rolande]

if there's any interest.

There is!

 

[Bryang]

Yes!!!!

 

[Itchy]

Please share.

 

[Little John]

There is!

Ok - that's all it takes - I just didn't want to post into empty space ...

Preamble: I've got a Hunter multi-fuel woodburner - one of those big 'uns with double doors - it's supposed to run the central heating as well as the house - but all it does is heat the sky directly above my house. I can feed it with hundreds of £'s-worth of coal, and still shiver. 95% of the heat goes straight up the chimney - well sod that - I've had enough ...

There are many videos and websites devoted to rocket stoves, so I worked my way through a few last year ... and to be honest I was a bit skeptical about the claims being made - but I thought I'd make one for as little cost as possible, if only to test those claims. Now I fully accept that ceramic construction is the way to go - but I've got steel, and I can weld - so steel it will have to be at this stage.

The first job is to find a suitable container - I chose a 47kg propane tank - and removed the valve (there are much easier ways than belting it with a hammer that some videos show) before filling the tank with water - which is ESSENTIAL - before cutting it open with an angle grinder. I then fabricated a firebox and welded that in place ... which takes us to the first pic:

This is where I got to last year, before running out of time:

So the next job was to weld on a 4" s/s riser tube:

I then surrounded that with a 6" tube and dropped some fire cement down to the bottom to hold it in place, and filled the cavity with perlite. This shows a small fire being lit in order to 'cook' the fire cement:

Now - this is the best bit: Look - no smoke ! Ok , it did smoke for a few minutes until it got up to temperature - but from then on, zero smoke.

I was so chuffed at this that I quickly plonked the top on, and lashed up a flue - which was not strictly necessary, but I wanted to simulate 'the real thing', as a test:

Just a handful of pieces of scrap wood, and the tank became so hot, there was no way it could be touched - at one point even some of the paint started burning off. But that was enough as a test - as I didn't want to stress half-set cement so early on.

There's just a few more jobs to do - I welded on some handles this afternoon, to make inspection/cleaning etc easier, and I need to do more work on the firebox door tomorrow.

But - this technology really does work - it's not exaggerated as I suspected it might be. It really is possible to heat a house with 1/10th the wood of a conventional wood-burner, that is already very clear.

LJ

 

[wessexmario]

some years ago I made a shed rocket heater using a large catering size tin and a 6ft length of cast iron drainpipe. The cast iron worked a treat as being 6ft tall it had a good draw and once it was warmed it radiated the heat nicely.
It's amazing how little fuel you need to create a lot of warmth with one of these things.

 

[REDWOOD]

I made one earlier this year, I put an old cut down aluminium keg on the top to boil frames

 

[Itchy]

Is there more detail on the firebox?

 

[REDWOOD]

The reason why they are called rocket stoves is that when they get going the drawing sound is like a rocket, the fire box on mine is just a "L" shaped pipe, the paddle divides the fire box in two where the sticks are placed above it and the air is drawn in below. Mine is filled with vermiculite which keeps the heat in so the flue remains hot to super heat the gasses making it a clean burn. A very efficient stove that will boil a kettle in 3 minutes with a hand full of twigs. I removed all the paint with a disc sander and repainted it with two coats of black heat resistant paint.

The down side is you need to continually feed the fire by pushing the twigs in and an alternative design would be to angle the feed tube up by 45 degrees so the twigs will fall into the fire

 

[Little John]

Well - I must say that you guys have been hiding your lights under a bushel ! Seems like I'm playing catch-up on this one ...

Is there more detail on the firebox?

Firebox ? - well, not really. To be honest I don't really know what I'm doing - I've just got a handle on the basic principle, and am now flying by the seat of my pants, so to speak.
I'm only using those materials I already have around the place. My thinking was (rightly or wrongly) to use a whacking big firebox to hold as much wood as possible, to save constant re-filling, and a small(ish) diameter riser pipe to create a kind of venturi effect as this is the smallest diameter tube within the system. I'm tempted to retro-fit a vertical feed tube - something around 6" diameter and 2ft tall (with an air-tight cap), to accomodate half-length pallet planks - but I don't want to get caught-out by not finishing before winter again. So that can be next year's project.

I made the firebox from lengths of odd-angle (2" x 1" x 7mm) which I have lots of. It's bloody heavy stuff, and should last a long time despite being mild steel.

I fitted a s/s tray inside the firebox with tubes underneath - these tubes are to support the tray as it's only thin stuff, and also to allow air to reach the base of the riser tube for a secondary burn. The riser tube itself had to be s/s in view of the high temps inside it.

I'm still working on the firebox door - I saw some other guy use a slanted front with hinged plates, which I thought was a rather neat idea, so I've copied that. I don't know whether I'll try and regulate air for the secondary burn yet - I'll need to run this a few times to get a feel for how it performs first.

LJ

 

[mintmoth]

...The down side is you need to continually feed the fire by pushing the twigs in and an alternative design would be to angle the feed tube up by 45 degrees so the twigs will fall into the fire

build it like this:-

I bookmarked several sites on R-M Heaters when I first heard of them as I liked the idea of a stove with an integral butt-warmer (in preparation for winning the lottery and building my own eco-house - alas, still waiting) http://www.richsoil.com/rocket-stove-mass-heater.jsp

 

[Canary Honey]

Could one of these be automatically fed such as with many biomass boilers? (pellets, chips etc)

 

[Little John]

This is the sort of thing I intend installing & testing, during the next phase of 'rocketry':

The drill being - start with ash pan flap closed and the top cap in position. Start a fire above the grate, and push a few lighted sticks towards the riser tube if necessary to start the draw.

When a good draw develops, then close the front door, open the top cap and load the feeder with sticks. Replace the top cap and open front door. Regulate air intake as necessary.

When re-fuelling: close front door, open top cap s_l_o_w_l_y to allow any smoke to be drawn downwards, and then re-load feeder. Replace top cap and open front door, regulating as before.

Good theory - but dunno what will happen in practice.

LJ

 

[Little John]

Bit of an update ...

I've just posted a thread with more pics over at the 'Permies' site:
http://www.permies.com/t/41349/rocket-stoves/Rocket-Heater-Build-pleased#324163

I'm thinking that this would make a very nice bee-shed heater ...

LJ

 

[Tom Bick]

Have not looked at all the replies on the primates site so don't know the what they have said but I think your idea of trying to control the burn with air flow is perhaps a good move as far as I am concerned. Always thought they are good stoves but once going well I bet you have to constantly feed them and you will be up and down like a yo yo With the only control of heat output by letting the fire burn down low with the risk of letting it go out and requiring more close attention. I know you are well into your design and working with scrap at hand but it would be interesting to see a conventional wood burner with back flue acting as the fire box of the rocket stove so you would perhaps have all the benefits of the two stoves.
I have one concern over the design of the rocket stove and perhaps more so with controlling the airflow and it's build up of tar resin ect that could catch fire one day and then that could be a sight to see.

 

[Itchy]

From what I heave read, the creosote is burned off each time. I suspect when the burn is slowed, than creosote will be formed.

 

[Little John]

As you know, I'm new to this - but what appears to be happening is that the creosote/tar etc is burnt-off ok when the heater is up to temperature - but during a start from cold, a small amount of creosote/tar is deposited on the internal surface of the tank. I noticed this when fitting the glass rope seal after just a couple of days use.

Right now it's just a 'wetting' of the surface, but multiply that by 3 months of cold-starts, and it could develop into a millimetre or two of build-up - so I'll need to keep an eye on that.

Otherwise - all is well. It's a bit of a fag feeding the heater of course, and life does tend to revolve around it, but I've always found that to be the case with any woodburner ...

LJ

 

[enrico]

As you know, I'm new to this - but what appears to be happening is that the creosote/tar etc is burnt-off ok when the heater is up to temperature - but during a start from cold, a small amount of creosote/tar is deposited on the internal surface of the tank. I noticed this when fitting the glass rope seal after just a couple of days use.

Right now it's just a 'wetting' of the surface, but multiply that by 3 months of cold-starts, and it could develop into a millimetre or two of build-up - so I'll need to keep an eye on that.

Otherwise - all is well. It's a bit of a fag feeding the heater of course, and life does tend to revolve around it, but I've always found that to be the case with any woodburner ...

LJ

I run three woodburners in my house.....I don't have a problem with constant feeding! Get them up to heat get it ticking over, always put one piece of wood on top of the burning one, will burn all night like that! And I sleep for eight hours! Also depends on what wood you are burning of course!
E

 

[Tom Bick]

Yes but what's the size of timber you can get in your wood burners enrico every rocket stove plans I have looked at are all based on reasonably small fire box. I can keep my 4kw stove in all night with wood but it requires some hardwood and even then it can either burn to fast or go out. For the dead of winter I prefer a few bags of coal for burning overnight.

 

[Little John]

Well, I was rather thinking of woodburners in comparison with gas, electric or oil - where you never need look at the heater, not even once, during the day. With any kind of solid fuel - even an open fire - it seems there's always something to do; chuck some more fuel on, rake over the coals, empty the ash - so different from just flicking on a switch and letting it happen.

But - I'm currently working my way through a mountain of pallets. There ain't much heat there (compared with ash, oak or apple) but it's free - and heating the house for gratis has a very good feel about it.

LJ