RMH smoking back after small changes

Yes, relocate the manifold to push directly into the other room, that will give up some of the push from the falling exhaust, but a good chimney should provide enough draft to compensate, and you still have the rise of the flame through the riser to push it.

But before that,  just for fun, you might remove some of that extra mass you installed near the manifold and substitute an elbow for the t--I think you said that was one of the changes you made?

And the first video clip you put in, though burning strongly, did have a hint of the pulsation in the background, and if the mass warming up causes some sort of inversion in that 3' rise outside the bell, that could be just enough to make it falter.,  but I'm not putting any money on any of these suggestions, But again, after seeing your diagram, that's a whole lot of twists and turns in a relatively short space

I have to imagine that this is so finely on the edge between working and not working, any little thing might be the culprit, so a leak in the chimney, a slight change of an angle on the exhaust pipe, , a change of wind direction, wind speed, maybe even if you just breathe too deep :-)

Another possible rebuild might be an expansion chamber, secondary bell in the other room instead of that right angle that sends it along the wall, so the manifold exhausts more or less directly into an expansion chamber that extracts more heat, then goes to the other right angles and up the chimney.


When you figure it out, let us know.

Hi, Bob
I want to appologize for my heater. I usually don't bother other people about my problems. It must be something really special that I can't sort out myself.
No changes have been made from manifold onwards.
When replacing bridge brick, I did not remove any cob and hence rebuilt feed tube with insulation in place. It might have left some gaps. But since people often use second air supply, I thought it wouldn't be a crime.

I started this thread hoping for an easy solution. Looks like it is not easy to tell even for experienced builders.
I am in for more rebuilding, it appears. But that's okay.

Today i fired it and tried to be meticulous.
It is windy so draft was improved (spinning cowl).
Rocket started out allright, though there was some indecisiveness of flames towards the back of feed tube. First pulsing started about 30min after. Lasted maybe 5sec.
For the fire lasted less than 60min (but still temp in the other room reached over 26C), there were 3 times it pulsated. All innitiated while gently rocking sticks to drop down (which normally would increase the rocketness). Last of the 3 was so pronounced that sent the house vibrating before I maneged to grab phone and make this clip

About 45min in, I had a feeling bell was very warm and was actually surprised to find out how hot chimney was (the last times, chimney would cool down when bell was hot, as if hot air was trapped inside it). I think it has not been this hot in any of last firings (and before that I had no need to check it). It actually stayed very how even when only ambers remained inside the feed.
Unfortunately, hot chimney did not stop flames from climbing up longer sticks. Which is unacceptable with 60min fire. It would never do that even after 3h of operation.

One interesting fact I noted:
I was very worried about the crack in manifold. So today decided to open manifold's cleanout. I mean, it wasn't wide open, but enough to let sunstantial amount of cold air in. This did not seem to make any change inside burn chamber.

Last thing before total rebuild will be to swing the bell slightly towards the room. Making that drawing yesterday, made me think that the part of it which is most offset (and hosts most of gases) sits too much on manifold which may be producing too much of a 'step' (and thus may be the suggested earlier restriction). Yesterday I stuck my hand through the cleanout hole and that 'step' may be about 3/4'' right over the 90deg exit elbow.

I appreciate all your suggestions, Bob. Truth is, since there has never been a single hint about not drawing properly, I  don't want to start messing with other parts at this time, because that may create only more potential potentials
For a while I was overwhelmed with work, but it looks like I now may have some time to do it.

Before any one has chance to reply (and I mean you, Bob, because you are the main contributor), I will add this

I am sure there is something different about the rocket. Nevertheless, I am starting to think that there also may be something wrong with me. That I am impatient and perfectionist, I have always known. And the two may be causing the issues.
It is warm outside so I only fire this heater for testing. In the beginning it was always fired cold. For the past 3 days, I have tried to be sistematic, but still... not like in winter.
Bench gets warmish on top, but the bottom does not get even close to what it did in winter. Back then, floor around it was warm too.

Before all ambers disappeared, I added kindling and twigs to start fire again. It is windy (and so the cowl helps with draft), but it is also warm (at least 15C/60F).
I got VERY strong draw. Chimney was (still is) VERY hot. Though there is still this 'laziness' at the far end of feed (the bottom far corner, ie), fire only started creeping up when I stopped adding fuel.

I want to sort it out more that any one in this thread I am going to open doors and windows and keep firing twice a day for a couple of days.
Until then I suspend this thread I just don't want to waste anybody's time, in case it is just my being picky.

BTW, with very stron draw, there was no panting, which (at least in my head) it doesn't make sense if there was restriction somewhere in the system... Of course, draw would pick up and then slow down again according to wind speed, but with such a strong draw (I wish I had videod it) why wouldn't it pulse? It did at the end though, when I left too little a gap between bricks to restrict air, but stopped immediately once I widened the gap to ca 15-20% CSA.

John Goodbody wrote:Last of the 3 was so pronounced that sent the house vibrating before I maneged to grab phone and make this clip.

Sent the house vibrating? That isn't a slow pulse but a full-blown pulse jet sound, probably at 40 times a second! You doesn't say anything about fuel consumption while it is doing this but in my experience the combustion is accelerated greatly so the fuel is racing through. Below is an example of what my 4" development model was capable of 7 years ago. I'm still in the dark what is causing this, sorry.



Your RMH is acting as a valveless pulse jet, see Pulsejet by Wikipedia.

Hey John, it's no big deal to ask us all , especially since we are learning new things too.  It's not as if anyone came up with a decisive answer immediately.
You actually have a lot going for you, and I'm sorry if some of the suggestions I made were a bit extreme.

My own preference , is to lay the sticks in the feed  with the top of the sticks leaning slight towards the fire tunnel, this helps keep the fire from climbing.


when fuel gets low, I also tended to block the top of the feed tube with a partial cover --as I think you said you were doing.

You talked about gaps in the feed tube where other air might leak? are you saying the burn chamber may be getting air from places other than the top of the feed tube?
When you talked about closing off the air supply starting a pulsing, and possible air leaks into the feed tube it made me think maybe your issues have less to do with the draft side  and more to do with the supply side. I have also been able  to stop and start pulsing and smoking back with partial blocking of the feed tube or simply  rearranging the fuel.


Peter alluded to the speed of combustion of your fuel. DO you have any actual temperature readings of the exhaust where it goes into the chimney?

I'm starting to wonder if maybe your draft is so strong it may be pulling the exhaust too fast at times starting the pulsing- in combination with other parts of your special configuration.

You talked about being too fussy, but your video pulsing was so strong I could feel my computer jumping on my lap. Still the answer may end up being quite simple no matter how dramatic the symptom,  again keep us posted on what you find

Hi John;  I've been quietly reading posts and not having any answers I found no reason to post.
After watching and listening to your video, I suggest you experiment with removing your spinner cap.

I know on some builds they are essential for good operation. On my builds and I believe on the majority of builds only a standard chimney cap is used.


It is a long prosses to completely dry out cob. Until it is 100% dry your draft will be effected.   I'm sure yours is dry by now... maybe you will not need a spinner cap any longer?

Thomas, it was only a joke that Bob is the only contributor. Well, fact is that he is the main figure, but I didn't mean it in a mean way

Peter, I'm sorry if I didn't descibe it properly. Didn't know how to put it well. Thing is, it isn't always like that. Sometimes slower pulses. But this morning it was the only time it scared me. To be honest, maybe it shook the rocket itself and fixed it for subsequent firing
Thanks for the link. I will read about it and maybe will figure something.

Peter, Bob
Since thses days I never get to fire it for longer than 60min, I only use twigs... max dia 3/4'', olive and almond prunings. They generally burn quickly. I have not seen anything unusual.
Actually, when pulsing, draft was very poor. When I re-fired later on the day, it amazed me because it pulled really strong. Really loud.
The reason for my second post earlier today was to share with you, guys, that the panting disappeared when draw improved. I have never experienced it before (pulsing) and from what Peter said here and on donkey32, I understood that stronger draw would actually escalate this pulsating. But it was gone altogether.

Bob, I am glad you take time to suggest all that. It's just that I don't want to go too deep, because it must be something so small that we (myself!) have overlooked.
That's why I have taken very seriously what you said earlier. My system may be on the edge of working or not. Maybe a small thing affects it. That's why I want to warm it up as in winter and hope it works. Meanwhile, I try to compare how it workes when I make small changes. Today I opened not only the manifold but also chimney cleanout. The latter cause fire to stall a little (and that was during the strong draw), so I realized that maybe hammering the tap on a little more or sealing it with aluminium tape will help. Then do the same with other cleanouts.
All has worked without those measures, but perhaps something small has changed...

When I commented about feed, I meant that I didn't necessarily do best job rebuilding the thing once I replaced bridge brick that cracked. Problem is, those bricks there have always been loose. One even kept sliding away, leaving 1/8'' gap where burn chamber starts. cracked bridge brick was loose too so not air tight at all. But the system worked great. That's why I didn't bother removing cob and insulation while redoing that. Even though I remembered that when last year I had similar problem (lazy flame at the far end of feed), redoing all brickwork (including heat riser and insulation) improved draft.

Thomas,
I wanted to remove the cowl. But since it was silicioned it (to stop it from rocking in VERY strong wind), I hesitated
Since you suggest so, I will do it tomorrow. I have almost 30C in the house and bell still warm so no need to fire this evening Top bench is warm and bottom is getting there too. So if my last theory about cold mass is to be true, I should have nice draw in the morninig! Fingers crossed. Maybe I won't have to touch the bell (although I already removed stove gasket due to curiousity

And please, ignore me next time I say that no one reads this thread it was my hopelessness laughing

I keep forgetting to add this
During the first firing today, with poor draw and panting, once flames started climbing up, fair amount of smoke was released (it did travel down though). I imagine it was due to lower temps in mid section of feed tube, as compare to burn chamber. This itself might have produced more charcoal and thus still weaker draw... Does it make sense?
In winter, I did have fire half way up feed tube, especially with a log inside. But have never seen any smoke like this. And flames always would point straight down.
I just hope that tomorrow, before most of you wake up, I will have good news

Hey John, how about testing for leaks. Say start a fire and then seal all inlets and outlets. Smoke will find its way to the leak. With regards to vibration I see it as air speed inside as vibrating back and port. Why not add a length on the stack say 1 meter. Hot air will always have the tendency to go up. When its hot enough in the barrel the flue gas will tend to rise countering the downward flow. Thus at some point it becomes a tug of war between flue gas trying to go up in the drum and flue gas trying to go up the stack.

Hi, Julian

I'm afraid I don't have another legth of pipe. It would need to be insulated too, otherwise I have no means to secure it.
It has been brought up a couple of times. But no easily done here. Middle of nowhere. They don't deliver to PO box... I may have to go to Madrid soon so could look for maybe 0.5m at least...

I didn't know how to test for leaks. Your idea seems good. Have you actually tried it?
My problem is I am alone here now and it will take time to climb up the roof and back down. Will it not cause much problems? apart from some CO, I imagine?

Forgot to add
Bob asked about chimney temp.
When I said it was 'warm', I could hold my hand on lower part, by the 90deg elbow. And when I meant 'hot' it was impossible to touch it at all. I have no way to measure now. I plastered the only place thermometer would sit. When measured last year, it reached between 80-100C. cannot be more exact. I imagine it was this warm today, during the strong draw.
On the other hand, lowest part of chimney would be around 50c when not drawing well.


Where exactly do you mean, Julian, air would speed back and forth? Burn? Heat riser? duct? I am not sure if I understand

Edit:
So in theory, we are talking about improving draw... warm bench should do it too, right?
Only asking as I want to reasure myself about the latest lead

julian Gerona wrote:Hey John, how about testing for leaks. Say start a fire and then seal all inlets and outlets. Smoke will find its way to the leak. With regards to vibration I see it as air speed inside as vibrating back and port. Why not add a length on the stack say 1 meter. Hot air will always have the tendency to go up. When its hot enough in the barrel the flue gas will tend to rise countering the downward flow. Thus at some point it becomes a tug of war between flue gas trying to go up in the drum and flue gas trying to go up the stack.

I see what you mean. It may be the case. As I implied earlier, sometimes I had a feeling hot air was trapped in bell and wouldnt go up the chimney.
I am still a bit afraid to add another 1m to the stack... it can blow real hard here. very strong gusts. I would not want it to crush fibrecement roofing...

I any case, should that be it, I have a good feeling about running this heater with bench all warm.

Yes I normally do this when testing for leaks on gasifiers . I havent constructed a RMH I'm from a hot country. You mentioned that problem occurred when you add inch/s to the drum height. Looks to me like you struck the perfect balance of hot gas in the drum trying to go up and the hot gas on the stack trying to go up. why not lower the drum to its original height.

Not at all!
Raising drum was one of suggested sollutions
Problem occured out of nowhere.
I painted barrel, replaced as it was (1/2'' lower it appeared) and changed one bridge brick.
Since then heater never has been the same... I mean, not anymore as it used to be.

Paint acts as insulation too. It means you are not dispersing heat as much as before. Thus the drum gets hotter on the inside. The hotter it gets the more resistance to downward flow of flue. When enough heat in the drum  reach the point where it counter balance the draw it starts to vibrate. After the vibration you loss draw and smoke starts to flow back. this means that the upward force of the hot air in the drum has overcame the draw. Try to run the RMH and when the vibration occurs and draw stops cool down the drum by spraying with water mist or wipe with wet rug. The draw should restart. If not then I am barking at the wrong tree.

Now we're talking!

Hahaha
I hope nobody reading this thread will think I am lazy, because I am far from that!
But Julian's posts are what I was hoping for

Bob, I am sure your ideas and logic are correct. But I could not stop believing that sollution must be in the parts I have touched I hope you know what I mean

Julian, I can't wait to try out 2 of your 3 suggestions (can't add another pipe until I get it). Actually, I pulled stove gasket and tried rocking drum as I wanted to replace it with another i have. I was more thinking the paint gasing or pin hole in the drum, but it is all the same to me I am not happy about the smell it gives off anyway. I thought it wouldn't because it is a stove paint at the end...

I don't know if you are barking at the wrong tree
I know I painted inside and out. And I said from the very beginning of this thread that drum was way hotter than before.
This is why I am so excited about your reply and about trying it out.
I was thinking how to do it... today tried fanning back of the drum. that's the hottest place (manifold is widest and bell is so close to vertical pipe I have there).
Heaters are not my thing and I don't know much about them. The Wisners' book was source of almost all I know.

Thanks, Julian!

You're welcome mate we are all teachers and learners as Bob said.
What's happening in there is that the hot gases starts to cool down as it hits the drum and should start to go down. when you painted the drum it does not sufficiently cool to go down.
Also from experience I found out that swirling the gas reduce friction considerably no matter where you use it. I use the concept on my cars exhaust and intake, have use it on stacks it always have positive result.Vortex is the natural motion everywhere. thats why the water drain normally takes the shape of vortex. Also if you have a small fan and you direct it to the drum it will increase the efficiency. Air/fluid velocity inside out increases heat transfer. If it where mine I will enclose the drum with another cylinder, force the air from below the drum with a small fan and have a muffler at the top to direct the hot air where I want it to be. or simply have it hit the ceiling and disperse around the house. The suction of fan should be position in the lowest area following the concept of temperature gradient of the space.

A second drum? I see the concept. This way, the inside one doesn't have to be painted too. I have a few drums that I was going to take down to scrap yard. May experiment with them.
Anyway. First things first.

I had a really strong draw. It is still windy, which helped. Though I have to removed the spinner itself, I took its cap off so I don't know if rotating blades made any difference, because gases were free to go straight up (blades are on the outside; centre has only a cross that holds them in place). When came back in, I thought that this had improved draft, but it is normally loud and think I have this impression every time I enter the house.
Throughout the burn, I also kept cooling the bell, as advised. At first, I thought it improved draw but I'm so eager to solve this enigma that my hopes can deceive me. In any case, while cooling the drum, first with wet cloth and then spraying water, I realised that the bottom MIGHT (I do not have a digital thermometer and a fluid one that I am using will not give me realiable readings) have been warmer than the top... Should that be the case (and I figured it by the amount of steam and how fast it was produced), it may have something to do with the shape of this drum. Top of the inverted thing is corrugated (only gentle corrugations but still), while the bottom is plain. Since corrugation may decipate heat faster, the impression I had may be correct.

To keep this post as short as possible, at no time did heater show any signs of smoke trying to climb the wrong way out. Moreover, I did not see smoke (or steam) at the back of feed tube (flames there were sort of lazy, but pointed towards burn chamber and no smoke or steam were swirling there).
It pulled correct and strong even when only embers were left (at that point chimney's temp was as high as bell's, which is correct but would not be the case over previous firings).
Interesting and surprising was that the bell itself stayed quite 'cool'. I am sure it was due to strong draft. In turn, there was no need for cooling it, there were no indications of heat trapped in there and paint too did not give off almost any of the annoying smell (I actually forgot all about it, because it wasn't noticable).
Yesterday I sealed the thermal crack in manifold that I mentioned earlier. Because it only appeared during heating, I had to do it with hot manifold which dried mortar too fast and it is very brittle. The idea was to fill up the crack so it will not be closing and opening again. Not sure if my logic was correct. I read that epoxy resin should be used but one I have are for plastics and wood. Not sure it those could be used with concrete.
To test for leaks, I will have to remove spinner so didn't do it at the end. But just wondering if there would be need for that.

All in all, would the symptoms I have described in this thread be caused by cold bench and cold firing? Poor draw, chinmey cold while bell too hot, smoke back and stalling after 45-60min - all of these can be caused by poor draft, right? And a warm bench should improve it, especially in my design with so many turns in relatively short run. It isn't rhetorical question I would very much love if some one could confirm or deny.

I will keep firing, observing, changing, adding small things to see what they cause. There will be no wind on Sat and will be easiest to test for leaks


EDIT:
For the sake of learning, how far above roof can chimneys go safely? The insulated 250mm pipe I have used are only fixed to outside wall with stainless bands. Then every piece in the stack connects to another with a 'quick release' band.
My question is: how far up can this stack go safely without the need for extra bracing?
Mine runs along the highest point and so it may not be straightforwad to add support.
I asked this in the shop where we bought tubes but poeple there were clueless only showed us what to use to fix them to walls

John, The system been like that, tube turns, height of chimney and all and you said it was working well. Then you painted the drum and problem arise. What else did you change along with the painting? Scrape the paint first. then see what happens.

Hi John,

My first rmh I used a copper water coil around the barrel  doing basically the same thing you were doing throwing water on the barrel.

It took a really long time for my bench to get warm, and often my burns were less than 2 hrs, so the bench never got that hot.

It worked completely off the natural thermal dynamics of the j tube design, heat rising up the riser, falling between the riser and bell, and those two forces propelling the exhaust through the bench and out.

My  "stack" exited horizontally, so there was no appreciable draft.  The exhaust was always pretty cool- around 100-120 F  45C I think

A good rule of thumb, you can touch but not be comfortable holding onto 135F  57C --- at 150 F  65 c you don't want to even touch it (sorry, I did those conversions off the top of my head, they may be a bit off)

Anyway,if the exhaust has a very strong draw, you will see increased fuel consumption, decreased heat absorption for fuel consumed.

It would seem your wind conditions and spinner may have a lot to do with the functioning of your system, and like we discussed, with so many bends in such a short space, there will obviously be a somewhat impeded flow which will likely increase with the velocity of the exhaust.

It's easy to imagine the velocity increasing (with the resistance to flow) until it hits a stalling point, and then picking up again, stall, etc-- pulsing.

With a slower velocity through the system (which you seem to have created at different times by restricting air intake)  you can throttle down the pulsing until it disappears.

I have often had smoke back when I had my "no draft" system, especially if a gust of wind blew the wrong way, or if the wood was stacked in the firebox wrong, or the tunnel got clogged with ash...

Running a RMH requires a fair amount of artistry anyway, even with relatively uncomplicated systems. It would seem that with so many angles  in such a short space, you may need to become an artist at keeping the thing running smoothly.

Usually a flue damper is not recommended, but in this case with such a strong draft, you may want to throttle back on your exhaust speed according to outside conditions- temperature and wind, and develop a working knowledge of your individual situation, which might change minute by minute.

I'm currently running a batch burner, with a fan in the exhaust to replace the draft normally required.  recently my fan boke-- a lovely  little low amp 12v fan that just put a gentle breeze pulling out the exhaust.

The replacement is a higher velocity fan and the difference is quite noticeable- Having a rheostat on the fan would likely be the next step in slowing down fuel consumption but maintaining the appropriate draft. That would serve the same function as a flue damper.

This might be an alternative to removing the spinner, but would do about the same thing, only with a little more control possible.

At any rate, I can't truly experience your system from here, and even if I could it might still take quite a while to figure out the actual relationships between all the different factors you are dealing with, but I hope I've given you some ideas to think about as you are playing with this system.

I will definitely remove the paint but I don't want to do it just now. Don't want to let the system cool down until I am sure it works as I want it with warm bench.

To be honest, I don't think this strong draft a problem. I don't see an issue with fuel consumption... There are 300 trees and there is just too much of twigs and small branches. And this is what I like about this heater, that it works better with small fuel rather than logs. I would not even say that the fuel races through... It is hard to tell how much firewood I have used this winter, but I'd say about >1m3 of larger pieces (2-6'') and 1-2m3 of kindling/twigs (weight-wise it was less than the former, but volume-wise it was way more, hence not easy to tell) - that kept the house between 21-25C (70-77F). Few people round here would insulate houses and many would use open fire. Compare with them, I was very impressed by my results.

As for the hot chimney:
I don't worry about heat loss too much (this morning I reached over 80F with open front door, after just over 60min burn, using mentioned sticks), and am concerned about proper draw.
Last year, before adding 3m to the bench and making it into 'L' (if you refer to my diagram, there was only 8' length along the stone wall), bench would be WAY too hot (melted my camping matt) and chimney way hotter than now. Hence the addition of quite a few more turns.
Having said that, I am very happy when it pulls strong and loud.

I understand it very well that RMH require some attention and understanding from operator. Problem is that throughout this winter it has worked so well (sometimes I didn't even bother lighting it properly and would shove sticks in, then place piece of cardboard on top and light that! No problems lighting it this way! Such was the draw. Perhaps too strong when windy, but I could live with that), that is spoiled me! Maybe this has cause problems I have been dealing with: because I was not carefull enough or too impatient...

As I said, I will keep firing, then will scrape paint off the bell, perhaps try another one on and test for leaks.
I will test, compare, compile and report.
But I can see a change already. So I hope it is only my 'right now' attitude that is to blame.
Fact is, I have never seen another rocket. I didn't know what to expect. But perhaps the way mine behaved was not very uncommon.... All I wanted was my old heater nothing more and nothing less!

Julian, I remember you asked what had been changed.
I did paint the drum and partly rebuilt feed tube.
Last year I wasn't happy about the operation. It behaved in a way like now (some smoke and swirling of flames at the back of feed). I completely rebuilt the engine and added insulation, then extended bench. I was very happy about improvement. Perhaps it was far from an avarage rocket, but I was glad. This is why I hinted a few times about rebuilding again, hoping to fix it again. Would be easy, but I don't want to rebuild every year. That's why I insist on finding answers.

Time to report!

Although problems that are not logical in the yes/no sense are not my speciality (which is the case with my heater), I am inclined to say that this morning has brought me some joy.
To start with, following Julian's instructions, on Saturday I tested for leaks. Saying I was disappointed not to find any around the heater would probably be improper However, both cleanouts in the other room leaked.
Then, I swapped drum for another, unpainted and with no corrugations. It also turned out to be slightly wider towards the top (when upside down), which puzzled me because I thought I had used the widest one
This new bell is not yet embedded (last time I made a concrete ring around and spaced it with ceramic blanket, thought it would be much easier to reembed the barrel) and second leak test revealed some smoke there which I closed just for testing.
There was some panting. I was very surprised because seconds before it started, I'd assured myself about improvement in opperation.
System pulled nicely. Which, in absence of spinning cup and with some air movement outside, was a positive thing.
With correct draw, I could hold my palm over sticks and could easily tell good draft. Flames always pointed downwards (even from halfway up the tube) and top bricks remaind cool. One couldn't even tell much heat rising from embers.
Then the panting started and stayed there for about a minute. Airer hung 15' away was rattling. Even then no smoke escaped up and flames didn't seem to be changing direction. But obviously, with draw broken up, at least some heat started to climb up, warming upper feed tube. All in all, it was nothing to write home about, but worth pointing out.

To sum up, when fired every day, heater runs fine and I would like to attribute all symptoms described in this thread to cold firing and warm weather (actually, two days ago I was sunbathing for the first time this year - it's the climate here, two seasons: summer and winter). However, hints by other members have lead to improved opperation (sealing leaking heat exchanger and using unpainted barrel).
When this pulsing started, open front door didn't seem to make any difference. Neithere did partly closing feed or shuffling sticks. I forgot to spray drum with water, but, since ocstructions and restrictions have been pointed to cause this behaviour, I think it may have to do with my manifold. Closer look revealed it is slightly narrower than the bell. Perhaps I should have offset the last course of bricks I added two weeks ago. In any case, if I am to rebuild it, I will certainly try to use metal manifold. I now see why most people have them.

I think that I will now rest reassured until October or early November. Hope that cooler temps and different atmospheric pressure (as was also suggested here to be causing problems) will ensure correct opperation.

Twists and turns of my design don't help with cold firing. Nor does the distance between bell and chimney. Vertical piece that runs by the drum helps push gases, but then they have 3x 90deg elbows, 1x 180deg 'U' and final 90 deg albow to the chimney. Hence use of spinning cowl, but I think even more important is warm bench (and cool air sucked in through cleanouts didn't help much with that).

Any suggestions to wrap this up are very welcome!

I want to embed bell and I am tempted to lighly paint it... only outside but am afraid it could cause problems again... Maybe second drum, like Julian has suggested, is the way to go? Definitively cheaper than stainless bell

Looks like there is a lot of bend in there pipes and its possible its the cause of vibration. Maybe try a twister. I always use them whether its gas or liquid. Even on engines intake and exhaust manifolds it works great in organizing the flow and decreasing friction. Fluid always takes the path and form of least resistance. For instance a drain normally takes the form of vortex. Its nature. So maybe weld a couple of flat bar on the inside of tube in an "X" shape. grind one edge so it pits the tube.

Do not use stainless it has a very low thermal conductivity. You are going to have the painted drum situation back. https://www.engineersedge.com/heat_transfer/thermal-conductivity-metals-alloys.htm

I'm positive that a second drum will increase your draft. Make sure to put enough space in between and adound the periphery of the drums. Then also you want air to enter in between the gap at the lowest point of the drums.  

Why do I think it will increase efficiency. One- velocity of fluid affects heat transfer. With this arrangement there will be increase of fluid that rubbing the sides of cup. Two- Its going to draw air to be heated from the lower temp gradient. which means that differential temperature will increase and thereby heat transfer rate. In any case try to study the formula for heat transfer. Its going to tall you a lot when designing or trouble shooting.

Heat transfer formula fby conduction

Q = KA ( T hot - T cold ) T
      _________________
               d

 A is the cross sectional area,
          THot is the higher temperature,
          TCold is the cooler temperature,
          t is the time taken,
          d is the thickness of the material.

When you make changes please report back. This is not an ordinary case. I;m puzzled by the rattling. Never encountered it before in all of my projects.

Thanks!
I'm very interested and shall try it this week. I have plenty of drums. Only problem: there won't be much room between them... they are 94cm tall, 59cm dia of open end and 52cm the other.
So what about the hole? Should I cut out whole bottom or just drill small holes? In previous post you mentioned fan too.
Can't wait to see the result

Thanks for the heads-up on stainless. Glad I shared this idea. Otherwise I would make another pricey mistake

The rattling airer (I figure that is what you refered to) was just the consequence of pulsing. These stone walls don't seem to be dumping vibrations. I have a diaphragm water pumped fixed to large boulder and it doesn't reduce the noise. When heater started panting, house started vibrating. Just now I had a thought which part of RMH would start these vibrations. Most likely it would be duct (which might have 'loosened' somewhat when I hammered cleanout caps in...), but could also be the floor... I really don't know what will be causing this. In 60 mins it appeared just like that for 60sec and just like that it disappeared... It was like... like something abruptly blocking strong draft. It certainly felt so around feed.

Looks to me as if there would not be enough air passage between the drums. But that's basing on guts. I will suggest using small fan instead. 60 watts around that. have a suction as low as possible. To take care of cold zone. I will make you a drawing when I find time.

Back with the drawing. We had this bad weather the last couple of days, so I stayed home glad that I'm not bored making this. No it does not take the whole two days to make this:)

Be aware that I have not seen an RMH my entire life. should you choose to play with me, the risk is entirely upon you.

I'll play the phantom engineer and you take all the rest :)

Fisrt, since the subject is centered on heating an enclose space. It involves creating a good heat source and to transfer that heat to space. I've seen lots of discussing on making the burn more efficient and all but have none on how to transfer that heat conducted by the cap/bell drum to the surrounding space. And this is what we are trying to play monki with.

lets make this as scientific as a kindergarten. First since we are improving an existing RMH we need point of comparisons.
While operating RMH as is, Take sample temperature on floor and ceiling directly above at different points around the house. Of course you'd like to note the points as you are going to take the "after" as well. Also note the time when you start the RMH. After firing let it stabilize then take samples.

To the drawing. I chose the "with fan" design because the barells wont have enough space between them for a natural convention system. That clearance would be ideal for a fan system. luckily the fan system is more efficient even if you factor in the added electricity consumption by the fan. If you examine carefully the air will move spiraling clockwise in between the drum up around and out to the ceiling. That is because upon pulling the plug of a sink pull of water, here in the part of the world, the water takes that motion. You may want to try your sink  as well.

Option two:

By the way you need to know, your engineer has no license :)

The biggest issue I see with this concept is that it relies principally on heating air and moving that around, while the natural heating mode of the RMH barrel (and the rest of the mass) is radiation, which goes in all directions equally, not limited to horizontal, and heats all the walls, floor, ceiling, and people and objects in the room, without depending on making air hot. There is air heating as well from the typical RMH barrel, and a fan that moves air from the ceiling above the barrel down toward a cooler zone may be beneficial. It is important to take into account that moving air is an effective cooling mechanism, and moving air that is not sufficiently warm (above room temperature) will actually make people feel colder.

Glenn Herbert wrote:The biggest issue I see with this concept is that it relies principally on heating air and moving that around, while the natural heating mode of the RMH barrel (and the rest of the mass) is radiation, which goes in all directions equally, not limited to horizontal, and heats all the walls, floor, ceiling, and people and objects in the room, without depending on making air hot. There is air heating as well from the typical RMH barrel, and a fan that moves air from the ceiling above the barrel down toward a cooler zone may be beneficial. It is important to take into account that moving air is an effective cooling mechanism, and moving air that is not sufficiently warm (above room temperature) will actually make people feel colder.

radiation in this case is of micro wave. it travels very short distance. 1 or 2 meters away then you can no longer feel it. I remember when I was in Netherlands I have to sleep 1 or 2 meters from a box heater with open door to get the visible radiation as well. whenever I close the door I can no longer sleep from the cold.

What radiates from the hot barrel and warm masonry is heat, i.e. infrared radiation, which can travel considerable distances. A small "point" source will suffer the effects of the inverse square law, intensity dropping as the square of the distance, so you need to be close to feel it. A large mass spreads out the sources, so you can get consistent warming a good distance away. I experience this myself; my kitchen 20 feet away from the 6' tall RMH with a 4 foot high partition between is still warm when the RMH is active.

My friend I do feel that this exchange has gone beyond constructive discussion. Its all theories. As we say down here "debate won't cook you meals". But before I go I'd like to say that I have a 98% confidence that my design will work. And since I'm kind of short with cash right now, I am willing to bet my last $850 on that confidence. But first we need to ask Paul if gambling is allowed:)

I expect your idea will work to move warm air around the space. What I would find very interesting is a comparison of the comfort effect with a bare barrel, and the same barrel with the jacket and blower. Temperature readings around the room, including readings in contact with the floor, walls, and ceiling, to gauge comfort conditions, would be the best. Outdoor readings would also be important to ensure meaningful comparison.

Thats exactly what I wanted to see also. That is why my advice above for John is to take sample temperature readings before and after on the same time of the day. Because I wanted to know and let others know how much better or worse is the project. Thanks for reminders on outside temperature forgot to mention it.