2 Winter old Rocket Stove in a yurt. Review and Feedback!

[rocketyurts]

Hey folks,

This is my first post on this forum and first I want to thank you all for creating this space and filling it with life and knowledge! I took a lot from it building, fixing and tunining my first Rocket mass heater.

In this Thread I want to describe the building of my J-Tube rocket stove in my 6m Yurt (insulated with 2-3cm felt blankets).

Also as I am wanting to build another rmh for our community workshop I am most curious for feedback and views from the recent development and advice how to construct & measure better stoves.

You can find some pictures here:

jonglirium.com/wp-content/uploads/2018/07/rmh1.jpg - Bench still in construction

jonglirium.com/wp-content/uploads/2018/07/rmh.jpg - finished

jonglirium.com/wp-content/uploads/2018/07/rmh2-e1577186626539.jpg - feed tube and one day of fuel

Some Data about the Stove:

-System size is 16 cm (Diameter of the pipes)

-Riser: 134cm, Burn Tunnel 60cm, Feed tube around 25cm, Piped bench (4m x 1m x ,6m & 10m of Pipes +2x 45° angles)

-P-Channel with a piece of metal in the feed tube - but haven't noticed a difference in the burn

-3m vertical chimney (not insulated) exiting the bench outside the yurt

-The stove is submerged so the feed tube is at floor level. (see pictures)

-The bench built on the ground and is insulated to the bottom and the sides with a clay-straw mix that gets more and more dense around the pipes and towards the floor level, around the hot parts (the core & where the bench pipes are close to wood) the stove is insulated with rock wool

-flue exit temp. is around 19° C (the pipes are declining towards the exit and there is a hole for the condensating water to exit outsite of the yurt)

-barrel top temp. 180° C - 230° C

-bench temp. 28° C - 20°C (warmer closer to the core and cooling down along the bech)

-temp. where the barrel exits to the bech is around 50°C

We now spent two winters in the Yurt with the heater (also two without ) and it's heating up the place easily to 18-20°C with 2-3 loads of fuel and storing the heat in the bech so there is a temp of around 6-10°C in the moringin with outside temperatures around 0°C to -6°C.

The performance of the stove is quite steady and reliable it starts well from cold with a good draft. Only later when the heater is hot there is a tendency for burn back and smoke back if the wood is resting against the back wall of the feed tube. We found this is managable by covering the feed tube around 50% with a brick.

I am very happy for feedback and suggestions on this build!

My main questions are:

-Would you consider the bench to big? Should it heat up more? Is the insulation to the ground sufficient or is the ground acting as a heat sink?

-Are there solutions out there to fight the burn back along the hot back wall of the feed tube

-Does it make sense to implement newer designs like peterberg 's double shoe box into this system to improve efficiency and heat storage, another design i was curious about is satamax ' top load vertical batch but the thread seems to be cold... donkey32.proboards.com/thread/1803/peter-vertical-batch

Another thing i would be happy about if you could point me to a thread explaining how to measure and analyze the exhaust and efficiency of stoves like this, what equipment to use ect... i only found bits and pieces here and there.

Thanks in advance! Felix

 

[permaculturebob]

I'm not sure what can be said here to suddenly bring you up to speed on the many years of experience represented in these threads. I came on this forum about three years ago and learned about the batch box first, then came horizontal risers, DSRs, etc. I'm still trying to understand it all.

It can take a week to read through some of the lengthier threads, and even longer when you start to read the reference links included in them.

I'm guessing you are getting ready to start winter in earnest, so unless you have a place outside to do experimental builds it's likely a little late for hands on, but a perfect time to start reading and familiarizing yourself with the different things that have already been tried, and the ones that might apply in your situation.

I'm going to guess you put a p channel in a normal J tube, no batch box or port.

It would probably not have much effect since there is no serious pull on the secondary air supply , J tubes are designed to be used with unrestricted primary air, and metal in the firebox may interfere with burn temps, reducing efficiency.


If you don't have a firm understanding of J tube dynamics, that's certainly going to be another prerequisite to understanding some of the more recent designs. I'm guessing you already have some of that reference material

If you only need to run two fire box size loads each day maybe the J is all you need, if like me you run more fuel through your stove, then you will likely want to know more about batch box dynamics-- I would suggest you start with donkey32.proboards.com/thread/1998/batchrocket-eu-information-site

Then there is the DSR donkey32.proboards.com/thread/2341/different-batch-core-riser-all which ultimately fell out of favor, giving way to the DSR2 donkey32.proboards.com/thread/3503/double-shoebox-rocket-mark-ii
Along the way you will be introduced to many innovators and experimenters and perhaps be able to make a little more sense out of the science and art of stove building

My own experience on this site has dramatically increased my knowledge base as well as giving me some great tools and designs to play with, but they come with a fair amount of reading and rereading trying to make sense of everything just so I know what questions to ask.

As far as insulation for your bench, that's a huge question, and a topic all it's own. built on the ground like that you are probably losing half of your heat to the earth. It's impossible to say long distance without looking at it, put a thermometer in the earth under the bench  right after a fire, if the temp is higher than surrounding soil away from the bench you have your answer.

As far as the dynamics of managing the burn box on a J tube, it seems you already have some techniques, using the brick to restrict air flow and avoid smoke.

leaning the fuel against the leading edge of the burn box can also help keep the fire down in the box, and giving the thing a rest to cool down in between fires can help improve manageability.

I also found that ashes can accumulate in the tunnel and obstruct free flow of gasses so if you think you have too much smoke, reach in there before lighting the fire periodically to clean it out.

One thing I noticed is your temps seem a bit low for the top of the barrel, at least compared with mine. My top could glow so bright it scared me. I used to have 1/2inch water pipe coiled around the barrel and one time when it ran out of water it melted the solder on the pipe joints about 1/2 way down the barrel.

You reported 230C as your high temp on the barrel top which to my way of thinking is less than 1/2 what it should be, and while your J seems to be ok enough to use by your report except for some minor smoke issues after longer burns, There must be something else going on reducing it's performance.

I feel a bit pretentious commenting with so many more experienced people on the forum, but maybe the links I've offered can answer more of your questions.

[Orange]

Dec 24, 2019 3:59:28 GMT -8 rocketyurts said:

-flue exit temp. is around 19° C (the pipes are declining towards the exit and there is a hole for the condensating water to exit outsite of the yurt)

wow, that's total heat extraction. I like the submerged bench, it's like floor heating. Any looks like you don't mind the cold, that small j-tube gives little heat.

[Jura]

Dec 24, 2019 3:59:28 GMT -8 rocketyurts said:

We found this is managable by covering the feed tube around 50% with a brick.

Hmmm.. I did not play much with J-Tubes but AFAIR the exit temps to the bench were of about 200^oC
(well.. the barrel was partially insulated)

Maybe when you decrease the air inlet by covering it with the brick it may drive the stove incomplete combustion
resulting in lower temps.

How much condensate do you collect from a single burn?

Dec 26, 2019 10:59:56 GMT -8 Orange said:

wow, that's total heat extraction. I like the submerged bench, it's like floor heating. Any looks like you don't mind the cold, that small j-tube gives little heat.

Do you find the 16 cm system small ?
(insufficient ??) If it is capable of heating some ~25 m²  (my guess) of the yurt?
we dont know much about the insulation of the yurt and if the radiant heat warms it up to 20 C.

I just balk at a mere thought of waking up in 6^oC in the morning

[rocketyurts]

Wow i didn't expect answers so soon.. thanks a bunch!

permaculturebob - yea the plan is to take this winter to read and learn more.

I'm going to guess you put a p channel in a normal J tube, no batch box or port.

yea just a piece of metal hanging in the feed tube - there is enough pull behind the metall to suck out a lighter flame

If you don't have a firm understanding of J tube dynamics, that's certainly going to be another prerequisite to understanding some of the more recent designs. I'm guessing you already have some of that reference material

I would say that i know my way around the J-Tube by ways of building and fixing it - but looking for opinions from comparable setups

As far as insulation for your bench, that's a huge question, and a topic all it's own. built on the ground like that you are probably losing half of your heat to the earth. It's impossible to say long distance without looking at it, put a thermometer in the earth under the bench right after a fire, if the temp is higher than surrounding soil away from the bench you have your answer.

i'll do some tests with the thermometer -good idea! - we tried to insulate as much as possible towards the ground and the sides of the bench (straw-clay and rockwool)

leaning the fuel against the leading edge of the burn box can also help keep the fire down in the box, and giving the thing a rest to cool down in between fires can help improve manageability.

I also found that ashes can accumulate...

yep... aware of that.

About the barrel temperatures I'm also wondering - we have quite a big gap between riser and barrel top - around 6cm i think but i should double check that - it's just a bit tricky in the heating season we decided for this gap size to get more heat into the bench. One thing we were thinking that we might increase draft and burn efficency by adding a layer of rock wool around the riser (at the moment its a 6cm thick clayslip-perlite mix)

Jura Maybe when you decrease the air inlet by covering it with the brick it may drive the stove incomplete combustion
resulting in lower temps.

How much condensate do you collect from a single burn?

I will check the condensate amount! About the combustion ... i kinda hear by the noise when the air inlet is too small and the fire chokes or starts pulsing and we try to run it with as much air as possible.

Orange & Jura - curious about feedback - would you say it's a small system with too little heat output?

Is there a known thread allready on how to measure a rocket? i would be glad about some advice how to go about it. Then i guess this build would be also easier to analyse from afar.

[permaculturebob]

It's interesting that you say you have a strong suction at the p channel, perhaps the outside air at that point is cooling the rising gases rather than combusting them.  The J tube was designed originally without  any secondary air to the riser and burned quite efficiently,

 It was only with the reduction of primary air and a port design in the batch box that secondary air became advantageous.

I would try blocking or removing the P channel for a burn and see if that helps your temps

I was always fascinated by the idea that the j tube was supposed to have enough oxygen to combust the fuel completely, but not so much it burned away the steel drum top too quickly.

[Orange]

I had a 160mm j-tube and it couldn't heat a small 16m2 room (with poor insulation).

check out the power calculator here: batchrocket.eu/en/building#size

[peterberg]

Jan 2, 2020 15:56:33 GMT -8 permaculturebob said:

It was only with the reduction of primary air and a port design in the batch box that secondary air became advantageous.

Hmmm... Maybe, just maybe, you've got the wrong end of the stick here? The original p-channel was the one in the j-tube and although the benefits aren't that obvious, the Testo clearly proved it has a positive impact. More hydrocarbons are burned this way, plus the first brick bridging the tunnel won't crack as easily due to heat stress. I did the experimentation as early as 2011, you joined 6 years later. Maybe you've missed the thread about this development completely?
See donkey32.proboards.com/thread/355/small-scale-development

[rocketyurts]

hey there and thanks again for all the answers!

I've did some measurements:

one burn (one loosely packed feed tube full of beech dried in the feedtube after the last burn) yields around 125ml of condensate - light brown and sausage-like smell

I measured the temps of the bench (underneath the insulation (30cm Straw) and yurt floor construction)
with outside temps around 6°C the outer walls of the bench are around 10° with top temps of the bench in between 34 and 22°C

So i guess there is some heat loss to the around 40cm high air space underneath the yurt floor construcion and probably also some to the ground - but enough to call it a heat sink? Looking forward for your thoughts here.

peterberg yea thats the reason i tried the channel - the front stone is doing well about hydrocarbons i can't tell I would like to start measuring the stove - is there a thread already on how to go about it and wich testo to use?

Orange - thanks for the link to the calculator - does it also apply to j-tubes? i live in a 28.27m² yurt with 52.95m³ (insulation quite poor 2-3cm of felted wool) - the stove is heating up the place up to 22°C with 2-3 loads of wood depending on outsite temperatures - what exit temp did your flue have?

[Orange]

this is an interesting idea of total heat extraction with condensate going outside of house. Are your chimney pipes clean or there is creosote buildup?

since bench is not that hot, I guess heat loss trough floor isn't significant if bottom of your bench is 10C and earth is 7C.

that calculator is only for BB, j-tubes are way less powerful since only bottom 1/3 of fuel is burning.

[rocketyurts]

Jan 11, 2020 12:30:37 GMT -8 Orange said:

this is an interesting idea of total heat extraction with condensate going outside of house. Are your chimney pipes clean or there is creosote buildup?

since bench is not that hot, I guess heat loss trough floor isn't significant if bottom of your bench is 10C and earth is 7C.

that calculator is only for BB, j-tubes are way less powerful since only bottom 1/3 of fuel is burning.

There is a light black film on the pipes after 2 winters of full heating - you'll get a black finger if you swipe alone the inside of the pipes outside of the yurt... also the cleanouts (after manifold and in the middle of the two 45° bends) are the same.

Thanks for the feedback - so it looks like we did the critical things right with this one.

[Orange]

sounds good, I'm just amazed that you can live/sleep in such cold conditions

[permaculturebob]

Jan 4, 2020 1:02:55 GMT -8 peterberg said:

Jan 2, 2020 15:56:33 GMT -8 permaculturebob said:

It was only with the reduction of primary air and a port design in the batch box that secondary air became advantageous.

Hmmm... Maybe, just maybe, you've got the wrong end of the stick here? The original p-channel was the one in the j-tube and although the benefits aren't that obvious, the Testo clearly proved it has a positive impact. More hydrocarbons are burned this way, plus the first brick bridging the tunnel won't crack as easily due to heat stress. I did the experimentation as early as 2011, you joined 6 years later. Maybe you've missed the thread about this development completely?
See donkey32.proboards.com/thread/355/small-scale-development

You were right, the thread where the first p channel was created had escaped me. That puts a totally different take on what I thought was meant by the P channel mentioned in this post, too bad I didn't know about it when I was still running  a j tube rocket. Trying to balance burn efficiency and having the fire climb out of the intake box was an ongoing problem after about the third batch in a hot firebox.

thanks for the link