New to this ... New heater?

Hi folks,
I am new to all this and have been looking about for a while now but didn't have much speciffic to contribute or ask for that matter.

Well we are just about to start a renovation of an old stone build in Wales, UK and want to be thinking a little out of the box.

Apart from actual building, and keeping the water out, the first order of business will be to build and test the heating and domestic hot water systems.

There is a huge hearth and chimney in the house which is nice but hardly practical. However it would make an excellent site for an efficient solid fuel heater and a load of thermal mass.

After much reading and digging about on the net I think I have a concept that will work and I would very much appreciate your thoughts and comments.

The thought process is to use a rocket core and water as a thermal mass whilst also heating domestic water and making provision for the mas to discharge heat as warm air.
Why water, well because it can be moved about, I have given the idea a great deal of though and think I have some interesting and good ideas but then I am also aware that I actually know very little about the subject so I may simply be way off base.
I may even link up some under floor heating ... but I do not have the depth available for large ducts. (Not shown on sketch)

My thoughts by component ...

Core. (Orange on the little sketch)
Standard stuff, the best dimensional design I can find but with a couple of enhancements.
I plan to construct this from high quality for brick, it will have a single BC glass window in front of the burn chamber which will double as a clean out port.
Both primary and secondary air will be supplied from a duct via dampers, the fuel loading tube will have a cap.
The combustion air will be drawn from outside via the outer skin of a coaxial flue. The idea is to prevent room air being consumed causing drafts.
I will however be installing an HRV system to provide adequate ventilation as a separate project.
I hope to be able to achieve complete combustion for a range of fire sizes by varying the air flow, we will see!

Heat exchanger / radiant element ...
Think barrel but containing a two coil heat exchanger, two because I want counter flow when considering relative water and gas flow.
There are two heat exchanger coils placed one above the other and separated with an insulated barrier, probably refractory. A is the upper coil.
Gas exits the core and is forced through coil B by a cap stone, exiting into the radiant chamber. The gas must then pass through coil A before entering the flue.
Water is piped first to coil A and then to coil B. Both coils are fed from the bottom and connected with an insulated link. I am hoping that this arrangement will still thermo-syphon as the overall gradient is still vertical.
I plan to experiment with enclosing the radiant chamber and modifying the air flow round it with vents ... Not shown as I haven't though much about it yet.

Thermal mass and domestic water heating ...
There are two distinct elements here, a thermal store which is uninsulated, but inside an insulated box and a conventional insulated talk for domestic hot water.
The exchanger coils are directly fed to several tall cylindrical tanks, the thermal mass. Hot water flows first to coil A where it is heated by the cooled gasses that have exited coil B.
It then flows to coil B where it is further heated by the gasses exiting the core.
The water is then taken directly to a coil in the top of the domestic hot water cylinder where, depending on the temperature of the domestic water, it may or may not get cooled.
After exiting the DHW coil it is then piped to the top of thermal store. I have no shown it on the drawing but I anticipate fitting bypass valve so that the store tanks can be taken out of the flow if the DHW tank is cold,
this will prevent the cold water returning from the DHW coil cooling the store. (I may automate this)
These tanks will have a significant surface area and will quickly heat the air inside the enclosure.
Adjustable vents in the thermal store enclosure will determine how much heat from the store is allowed into the living space with a ceiling fan keeping the space air from stratifying (Ifs a high pitched roof)
The DHW tank will probably be the un-vented type as opposed to the type shown but that is symantics and wiull largly depend on what I can get a good price on.

I have no idea about water flow rates gas temperatures in various areas or how big the gas air exchange coils will need to be.
I also hope to get this working using thermo-syphoning alone but that may not be possible without a syphon stack in the flue space, also not shown.

I would very much welcome any and all comments but particularly those from anyone who has actually built something with these elements.

Thanks for looking
Al

Well I have to say I am a little disappointed ....
I defiantly wasn't expecting no response at all in fact I was anticipating a raft of negative comments and explanations of why my plan, or at the very least parts of it, was flawed, in fact I was looking forward to them, I cant possibly be right about all this stuff.

Ah well perhaps should have asked some specific questions ... SO ...

1.
I am finding some conflicting opinions on dimensions and could do with some help. Some posts suggest the burn tube should be smaller than the riser whilst others suggest consistent CSA.
I don't know enough to have an opinion and as I have no practical experience I am a little stuck.
Logically I find the concept of a larger core riser appealing as it will contain the hottest and therefore biggest volume of gasses but then there is probably a lot going on that I have yet to appreciate.

2.
I get that draw/draft is a product of the riser and its internal temperature and is finite. I also appreciate that you cant just go adding ducts and increasing the length of the system overall without reaching a point where the restriction of flow becomes fatal, to the burn that is. However, I am sure that I will be able to calculate the flow in a duct at a given pressure differential and I also appreciate that the riser is the pump but I have no idea how I would calculate the differential that the pump will generate.
For example will a longer riser give more differential and will a larger CSA provide less?
I get that a longer riser will offer a bigger resistance to the flow by creating a larger pressure drop so I cant just keep going longer to get more flow but could I go longer and wider to achieve a more powerful pump as it were?
(I ask because my proposed coils and intake ducting will need to be compensated for)

3.
If I build with refractory brick, smelting furnace liners that I may have access to, will that be sufficiently insulating or should I be thinking about a high temperature lining and then external insulation, be that granular or otherwise.
The bricks in question are used to contain molten alloy, sometimes even iron rich alloys, in steal casings. Since the casings don't melt, well not unless a brick has been knocked out of place, I assume that they must be reasonably good insulators.
For that matter if I simply buy fire bricks, the light insulating variety would I still need insulation around those.
I was hoping to dry stack the bricks/blocks, possibly seated Ceramic Fiber Blanket, for testing purposes.

4.
That said, bricks I mean, I like the idea of a cast core, mostly because it would be easy to build it 'round', with an offset burn tube so that a swirl would be introduced.
The problem is that I have found many different recipes for cast-able refractory, all different, and cant find much in the way of data with regard to the longevity of the different recipes.
I suspect a commercial product would be more predictable but would be very expensive to build and then scrap due to a floored design.

This inst about me thinking I know or can do better than the established norm, in fact I am painfully aware that a lack of knowledge is likely to make anything I build fail miserably.
I am about to move into an old house, and I use the term loosely, it will be a house again soon but for now it is little more than an organised pile of stones with a roof on most of it.
I will have no grid connections and a mammoth rebuild on my hands ...
I realise I could build many prototypes and get it right that way I really will not have the time so I am looking for a leg up as it were.

I am quite confident that the rocket design can be adapted to a room sealed variant with hot water extracting the heat but then I am equally confident that I don't know nearly enough to design one.
Pretty pictures and lofty goals are all well and good but the world is full of 'not designs' that don't work because they never progressed beyond the idea stage.
The only thing I do know at this point is that I cant build an idea, it needs to be turned into a design first or it will never amount to more than an expensive pile of rubble.

I suppose the last question needs to be ... Is this project so far out there that no one's interest is sparked, am I that far from the mark?
Folks, at least put me out of my misery if I am being silly.

Thanks
Al

Hi Alistair!

I'm no expert, but seeing as it's the weekend and most folks will be busy I thought I'd just stick my nose in and say 'Croeso i Permies!'

I'd recommend checking out this thread with links to Paul's podcast about rocket mass heaters, including the infamous 'Boom Squish', which is what he calls any rocket powered water heater as they are so potentially dangerous. 'Boom' is where it explodes, 'Squish' is what happens to you when the bits of the heater land on you.

I think it would be worth listening to what he has to say - it might give you an idea why people are hesitant in answering your question. No one wants you to go 'Squish'.

Thanks for the link I am off there now ...
I am an engineer, although I mostly work on micro hydro schemes and program PLC's, but still I am well aware of the dangers of heating water in anything potentially sealed and not controllable.

That said I also don't know, well anything, about the burn characteristics of this type of heater.


BoomSquash ... Mmmm I can see the requirement to learn, that said any other heater would / could explode if not properly managed and I expect that the systems used as safety systems, the low tech ones, could probably be employed to make a rocket based system safe.

Anyway, the link looks likely to be a good place to start, I may even learn some of the terminology so I can ask better questions.

Cheers
Al

Alistair Warburton : A late welcome to Permies, and a Big Welcome to Rocket Stoves / Rocket Mass Heaters, This is where I usually say,'' you will long remember your
1st few posts to the Wood Heaters / Rocket Mass Heaters'', and its usually true! In this case, I am sure that your fellow members will long remember your First Few posts !

I can easily say that your sketch is definitely one of the most ambitious First builds we have ever seen here at Rocket Stoves, it is clear the amount of work, skull sweat
that went into it !

The truth be told we talk more about over-unity machines - than we talk about home-owner-installed hot water systems ! If you have not already seen the
''Myth-busters Two videos'' on the Exploding Domestic Hot Water Tank, Please do ! Think the Boston Marathon bombing with multiple, full body, 3rd degree burns !

I'm sure that you do understand that simply applying high temperature refractory lining to a short section of internal chimney does not make a Rocket Mass Heater R.M.H.,
I would like to go over with you exactly why you don't think you have room for duct work- (and Thermal Mass storage ?)

There is/are several proposals for air brought in from outside, you are working overtime to provide clean air for your furnace and increasing the stagnation of your internal
air supply, and then tacking on an Air-to-Air heat Exchanger, Consider a positive pressure Habitation with high levels of moisture which penetrates to the frost level of out-
side Insulation, especially around windows, I have seen windows that could not be opened in winter, and even window glass that cracked due to swelling of the Frost !

Now consider a building with negative pressure resisting the transportation of moisture out through the exterior walls, preserving the insulation to do its job !

The J-Bend feed is there to make feeding the fire easy, and there is the best place to regulate the amount of primary air flow. Capping the air flow at the Feed opening will
require modifications to Feeding and fuel / air mixing that being outside the arrangement of a Rocket Mass Heater Will be virgin territory ! Also I am not sure that you Realize
that in order to achieve the storage of 24 hrs worth of heat within the thermal mass (stone, Cob, Or Water ) of a R.M.H. Will take approximately 6-8 hrs of close attention !

My understanding is that any application of counter-flow, (coils A-B) will negate any chance for a working thermo-syphon ! If I am wrong, please correct me ! Without a
working Thermo Syphon you will need a pump, and what will you do for heat if the power goes out ? Unless you can drain your coils down and positively prove that you have
done so you can't run the Heater at all - and if you are wrong you have your Boom Squish ! This seems like the right place to mention a Commercial Grade Boiler High Temp,
High Pressure relief valve, and the fact that you must still guarantee that your water valve controlling make-up water must be able to keep up with all water losses anytime
there is a Fire in your system !

This by itself would point away from any Un-vented System !

The Rule is To Maintain a Constant Cross Sectional Area, and Keep it Whole-y, Minor deviations are possible within the Burn Tunnel which is a separate entity from the Feed
Tube,when not Feeding the Maximum amount of fuel the air flow at the top of the Feed Tube gets frequent adjustments to match the flow of air to the amount of fuel available
to burn !

There is of course more flow of gas through a round pipe and figuring friction loss is much easier, realistically you would want a tall Heat Riser to promote flow and also a
maximum amount of turbulence to make sure you have adequate mixing of the hottest gas available to the coils contact area ! Your system requires an entire set of calcu-
-lations then those of the average R.M.H., It sounds like we will be coming to you to figure out flow rates and Temps and can should be able to connect you with people who
Speak the Same language !

I wonder if I can suggest to you visiting the Web4deb Channel at YouTube Land, scroll down to the Rocket Mass Heater Playlists ! This is a specific vented system,
custom built (D.I.Y.), for a Greenhouse, and may not meet your needs at all, but the cleverness of the build should be Interesting to you !

For the Good of the Craft! As always, your comments and Questions are Solicited and Welcome ! Think like Fire, Flow like Gas, Don't be the Marshmallow ! Big Al

Thanks so much for your time Allen,
I know that my post may look as if it came form someone self obsessed and not prepared to listen to reason or experience but that couldn't be further from the truth.
In fact it exists because I know I cant possibly have got this right with my first conceptualisation, what I don't know is how wrong I am yet.

This is one of those times when feeling a little deflated is actually refreshing ... All be it humbling at the same time.

Mass ...
It isn't about space, it is about hot water. We will be off grid with very limited power and being in the UK very limited sunshine for the most part.
I absolutely could have a stone / cob mass vertically or horizontally in the immediate vicinity of the core in fact that was my first thought.
However once I started thinking about how to add in a heat exchanger it occurred to me that, provided I could get it to work safely, placing thermal storage tanks in the same space that the stone mass and ducts would need to occupy would actually store more heat. E & E say in one of their vids or pod casts that water is the best heat store, just before going on to say you shouldn't mess with it unless you are aware of the risks and can design them out.

"Understand just applying high temperature ....... "
Alas no, I fear that enthusiasm got the better of me there.
I appreciate the need for the insulated riser but hadn't given much thought to how that was working as a 'pump' - my assumption not a fact.
I looked at the stove concept and simply saw a thermal pump but when I looked at the RMH concept I failed to appreciate that the very same pump was being augmented with a second stage, the cooling gasses moving downwards.

My conceptual sketch shows clearly that I failed to consider the system as a whole when thinking about the mechanism for driving the air flow. I am suggesting cooling gasses that are moving upwards which is not going to work unless the riser is capable of creating a great deal of pressure differential.
Is that something that has been measured or calculated ? How much differential is created in the riser and how much in the barrel in a conventional system?

I am not too discouraged as placing the heat exchangers in a section of downdraught is actually a far better plan and will produce the counter flow I need without reversing the water flow through multiple exchangers.


Air ...
A point well made but also one I have considered extensively. Since I want, in fact need, to ventilate when the heater is not running an HRV is almost a given.
The house is an old stone build and moisture would quickly make the space uninhabitable without significant ventilation.
The HRV will work with forced extract as opposed to forced supply so that the space is negative as this will give the best results as far as I understand it and it appears that you agree.
The problem that I envisaged is that the very negative pressure that keeps the space healthy would negatively impact the gas flow in the heater which is why I envisage using what will effectively be a room sealed unit.
Of course I may have overlooked something fundamental but provided that the ducts are big enough I don't at this point see why it wouldn't work.
However I am now aware that E & E abandoned an air supply below the feed tube as it was causing smoke back and I can see how that might be an issue which leads me to think that ducting the air would probably work OK but that I will need to have at least some primary air going in at the top of the feed tube.
I am also aware that the co-axial flue may be a poor plan as it directly works against the flow by cooling the exhaust and heating the incoming air which will/would reduce the flow of both!

"6-8 hrs of close attention ....."
Isn't that a function of the size of the heater. I get that a few sticks, however well they are burned, isn't going to heat much mass but then I wasn't thinking of sticks ....
There go's that box again, I just don't seem to be able to stay in it! Perhaps actually knowing where the sides are would be a good start

Anyway ... Part of the reason for thinking water mass is the ability to move it away from the heat source when it is hot and replace it with new cold mass. I reasoned that this approach would allow me to extract heat more quickly and therefore utilise a bigger fire. The second thought was to use more massive fuel in much the same way as a bale burner consumes the end of a bale that is fed in as it is consumed.
I am not suggesting that I will be burning bales but I hope to be burning the end off logs that are sitting on a 'grate' for want of a better analogy. (Concept sketch attached)
Primary air is drawn under the fuel, and probably a little from the feed tube to combat smoking, whilst secondary air flows under the grate support plate directly to the burn chamber.
The grates will be 3mm stainless, welded and will need toi be sacrificial I suspect.
I expect I will have to play with this in a mock-up to have any chance of getting it to work.


Water, thermo-syphon and Un-vented System ...
IT will not be sealed, that is just asking for an explosion, my reference to sealed was on the DHW side and even that is more risky than a vented system which is my preference.
You may be correct about the coil arrangement shown, although the flow in all the elements exposed to a temperature gradient is the right way.
Given that I now think the coil would be best placed in the down draft chamber, barrel in conventional terms, I dont think it will be an issue but there is a little trick that can be employed if I need more flow.
Ironically it works the same way a RMH does. You create a long vertical loop with its feed leg, upward insulated and the return leg uninsulated. The water cooling in the down leg gets more dense and drives the system.
Obviously you loose some heat in the process, you have to or no work is done but since the loop could be a nice polished pipe in the living space that isn't much of an issue.
This type of thermal pump was employed in large bore single pipe heating systems, mostly commercial, for years to drive water round horizontal pipes supplying heat to floors.

Calculations ... Well I suspect it will be more trial and error, OK probably mostly error, rather than calculation. I suspect that the thermodynamics and flow calculations required for such a complex space will be way beyond me even if I could find the information I doubt I would recognise it.
It is interesting that you say use a tall riser, that seems to me to be intuitively correct, but I suspect it will need to be a larger CSA to counteract the pressure drop.
My original thought process was to use a square riser, as I expect to be using kiln brick, but the cast solution is very appealing, either way I will offset the burn tube so that a turbulent, hopefully a vortex, is created.

I have already looked at Web4deb Channel and you are correct It was very interesting although I would not be keen on using aluminium fins in a potentially corrosive hot environment.
There is another design I like the look of but I will need to do some calculations on exchanger area as it may noy have enough without being stupidly big.
Heat exchanger on rocket heater - Apostol Engineering

I would be most interested to hear what everyone else thinks.

Pleas keep the questions and challenges coming, the more I have to consider and explain my thoughts in context's I haven't thought about the closer I will get to actually being able to build a test rig.
Or perhaps just starting again because I was way of base in the first place

There are some deal breakers here that may turn out to be insurmountable problems.
Fuel feed and long burn time being the one I am currently most worried about. I cant believe that feeding logs hasn't been tried and yet it I haven't seen a single example of this being done, that is worrying.

Looking forward to your thoughts, collectively
Thanks
Al

AL 2 AL : I typed up a serious, well reasoned an over-all a very positive missive and promptly sent it off into the great big Void !

Oh my ! all that deathless prose lost to humanity ! Will try later ! Keep thinking outside the box, we need people just like you to grow !

Think like Fire, Flow like Gas, Don't be the Marshmallow ! All comments,questions solicited and Welcome !

Thanks Al,
I look forward to your comments when you have the time, I hate it when that happens, so much so that I usually coppy and past to text doc before pressing 'post' I have been caught out too many times in the past.

The more I read the less I seem to know, go figure, I am hoping that the equation will turn round at some point so that I start going forwards.
That said I would rather find out here how wrong I am than when I am looking at an expensive pile of rubble!

I have been looking at cast-able refractory, commercial stuff it isn't as expensive as I thought, has anyone played with it?

it seems to fall into two basic categories, dense strong stuff and light insulating stuff which I expect is just the dense stuff with a filler. What I am finding suggests that one can be used as a backer, or face depending on your view point, for the other.

I find myself wondering about casting, well donuts, flat top and bottom faces of course, but with a rebate, circular trough, to enclose furnace rope as a seal between sections.
Spring form cake tin springs to mind, pun intended ...
The centre could be slightly tapered which would make it easier to remove from the mould and in service would create little ridges that might actually promote ambulance. ( The section is extremely exaggerated )

Anyone with casting experience? I would welcome a critique ...

Still thinking, feel free to chime in!
Cheers
Al

Oops, that should have been 'Segment' I don't want anyone thinking I meant 'Cement', that would be a bad thing

Hay just had a thought, with all this talk about shippable cores, what about segmented shippable core blocks, easier to pack, stackable to different heights, even replaceable as individual segments if damage occurs or the hottest bits degrade.

I don't know that much about gas but I would imagine that they would be gas tight, at least tight enough for a core with a furnace rope seated in matching groves between them, they certainly wouldn't be moving about.

Just a passing thought!

Al

AL 2 AL : With your experience with water head and flow you are very far ahead of us in actual knowledge of laminar flow and friction loss. Is the term Trip Wire familiar to you,
as I understand the way it is most commonly used around here, the trip wire creates a little turbulence down stream from itself and breaks up that static layer of water or gas
flow at the pipings walls, more mixing, faster flows. Anyway the Tripwire are of a size easily missed by the human eye !

I'm glad you know who E & E are, I want to send you to the Search Button in the Permies "tool box'' , click on that and then do a google search for the Thread Existing Chimney
within Permies (this works best for me) Permies' search engine seems more LeTTer CaSe literal! Part of my earlier lost post was 3 paragraphs on chimneys that Erica addresses
in as many sentences.

I was also going to suggest that you go to ernieanderica.com find and click on 'Consulting and Booking Events', to connect to and click on 'Site Planning', which will connect
you to Their Extensive if not all-inclusive form to allow you to plan your build with very little worry that you have left anything out !

Finally, If you go to Permies Sister site richsoil.com you should be able to find Paul Wheaton's R.M.H. Podcasts with Ernie and Erica, #019 is 1st I believe, that should keep you busy
Long enough for me to re-read everything you have already wrote, to see what I missed ! Think like fire, Flow like Gas, Don't be the Marshmallow !! For the Craft!

As always, your comments / questions are solicited and (generally) be answered Big Al !

Thanks for all the links Al, you are right it will keep me busy for a while.

Alas my experience with water is not at the expert level, mostly I do the control system design. Obviously I need to know how it all hangs together and works but I rely on the mechanical guys for the raw calcs.
That said I am a good all rounder, sorry if that sound a little immodest but it is why I have a job playing with systems I love to work on.

I haven't heard of the trip wire but then the last thing I would want to do with a hydraulic flow would be to break it up. You are correct that the boundary layer will move slower than the main body of the fluid but the beast way to minimise pressure drop is to keep all direction changes slow so that the boundary layer inst disrupted. laminar flow is just that, laminar, not all the fluid is moving at the same speed but critically very little of it is changing speed.
Once you mix things up pockets of fluid have to change velocity which requires some energy that will end up being dissipated as heat or sound.
In laminar flow conditions it is not unreasonable to think of the boundary layers as if it were a lubricant protecting the majority of the flow from the frictional losses associated with the pipe wall.
We typically recommend pigging a pipe at least once every two years, scouring it out with a sort of bobbin thing that the water pushes through.
This is done because even small irregularities, algae or general detritus, is sufficient to destabilise the flow and significantly increase the pressure drop. The actual change in size plays a small part but it is by far the smallest contributory factor.

"Use smooth pipe for your RMH bench ducting" .... its the same thing. ( I have seen this said several times )
Technically, the duct would perform better with long sweeping corners and bungs in the clean-out ports so that the 'T' leg was filled with something that matched the ducts inner wall.
Fluids simply don't like changing direction a 90 degree elbow will typically have 5 times the pressure drop that a pipe of the same length would exhibit.

I'v been thinking about your comments and reading associated posts and now have concept 2 in mind ... It may be no better than concept 1 but stagnant isn't an option.

The sketch is not to scale, mainly because I don't know what size things will need to be either in finite units or in relation to each-other.
I suspect that it will need to be tall and relatively skinny in comparison which should maximise draft in both the up-flow and down-flow sections.

I have modified the heat exchangers to be two large tubes for want of a better description, think barrel in barrel with the top and bottom cut off and a narrow flange joining the inn and outer skin. There are two of these inside an insulated outer skin.
I know a guy who can spool stainless up to 2m X 2m in material up to 8mm thick so a couple of spools from 1mm with nominal diameters of 450mm and 500mm respectively shouldn't be a problem whatever height they need to be.
Pipe fittings will be welded bosses. There will be a small vapour lock at the top which will partially bubble out when it expands but it will be no more dangerous than an air locked radiator in a vented system.
I may have a word wit Pete, my spool guy, it might be possible to slit a tube and weld it over a slot in the shell to give a vertical connection which would get rid of all the air.
I might even look at getting the case done that way, spooled I mean, if it isn't too expensive.

I have already found "Existing Chimney", it was interesting and provoked me into looking at the subject in general.
I have to say though, if I was facing a similar problem I would be looking at ways to put warm gas into the flue, either permanently with just enough heat to drive, it or possibly using a damper to feed it directly whilst starting.
It will be interesting to measure the relative pressures, I haven't seen that anywhere yet, but I suspect that the top of the barrel will be significantly above atmospheric and full of very hot gas, bleeding a little of that into an existing flue would defiantly create draft in a conventional way. The point is that peeping over the box lid as opposed to jumping out might work in those situations, sacrifice a little heat to mitigate the cold existing flue and keep everything else the same.

I used to work on naturally aspirated boilers back in the day and many of those, particularly the industrial ones in tall buildings had balanced flue dampers. Just a counterbalanced swinging plate really, that would open when the flue was too hot and drawing too much. The idea was that the flue was always going to draw enough even with the boiler very cool on a low flame but when the burner was turned up and the flue got hotter room air was sucked in through the damper protecting the boiler from excessive pressure differential.
If you were to turn that on its head you could have a mechanical mechanism that varied the hot gas to the flue based on the current draw, more draw less hot gas.
That way you would naturally start on bypass, for want of a better phrase, and progress to maximum flow through the mass as things warmed up and the flue started working.

I have listened to some of Paul's stuff, it seems very informative but there is a great deal of it and the format makes cherry picking difficult.
E & E's Vid, the hour long talk, was worth the effort though so I will persuasive with the pod-casts I think.

My last thought for the day is possibly a little contravention, Gasp !!
I was pondering long burn solutions and thinking about my log grate idea. Reading suggests that this sort of thing hasn't been that successful in the past and I found myself thinking about gasifying wood burners again.
And then ...
Well what if I were to build a fire box with a sloping floor, front to back and a rear grate leading to the burn tube. Primary air would go in through the box and round the fuel creating a pyrolysis zone at the rear and discharging gas and smoke into the burn chamber. Secondary air would then be introduced to complete the combustion.
Well so far that needs a fan and would actually be a pretty standard arrangement if it had one.
Now scrap the fan and use the thermal drive characteristics of the RMH in its place.
Basically what I am suggesting is putting downdraught gasifying fire box, all be it with a 45 degree burn as opposed to a vertical one, in place of the feed tube and part of the burn tube.
Now I appreciate that starting would need a bypass of some sort but that could be done and once the flue was pre warmed the system could switch to downdraught and heat the riser would quickly take over the job of creating draft so that heat could be extracted and the flue allowed to cool.

Is a gasifying / Rocket Hybrid possible? Has anyone tried this?

Al 2 AL: Hi !, Be advised that I have an anterior motive for 'bringing You up to speed', You too can spend hours on a computer talking to your fellow members ! I really like the
way you find a new angle to look at 'the Box' !

I agree that usually you do not want to increase Turbulence,Energy lost to Increased Sound (why do you think we call it a 'Rocket' ? ) and Energy lost to increased Heat (GOOD! )
We want that increased turbulence for the mixing of gases that make the 2ndary burn possible, ( Now who is thinking inside the box ?) The 2ndary burn will continue through at
least 1/2 of the Heat Riser / internal chimney !

In Commercial scotch marine multi tube boilers, you often find Long 'fins' looking like they were cut off of the end of a piece of corrugated roofing wwwwwwww slid into the length
of the boiler tube to break up the Hot Exhaust Gas flow, otherwise the hottest gases 'concentrate' in the center !

I was taught 2.5' for friction loss generally for an Elbow, but recently everyone seems to agree on 5', but i don't see that as any kind of a problem if you are not going to run your
exhaust long distances through a Thermal Mass Bench, This is a good place to talk about dampers, a common adaptation for cold weather Climates is running the horizontal pipes
thru the thermal mass that has been shaped to be Built-in-furniture. Then back close to the R.M.H., before being vented through an interior vertical chimney to pick up a little add-
itional heat ! There are several adaptations allowing the R.M.H. to exhaust directly to the vertical Chimney to warm it! This adaptation has proven to be useful when the R.M.H.,
and the entire house is cold and damp,actually colder than outside, under those conditions getting a 'good draw' needs both art and science ! Having said that, I stand firmly with
Tradition when I say dampers should never close off the flow of gases - That is the function of that J-Bend, which works like a the water/gas seal in the pipe bends under your
sink !

So yes, - you probably can Bleed hot exhaust gases off of the top of your 55 gal drum ! Why did you insulate the top of your Drum? it is part of the radiating surfaces needed to
cool gases ! ?

Al, take a deep breath and smile! There are lots of people working on Pyrolyzing wood and using the resulting Wood-gases to generate both heat and electricity on both sides of
'the pond' ! My personal Favorite is gasifying charcoal to run small generators . But, you would end up living in a Caretaker Hut 24-7-365 managing a large commercial Bio-gas
hybride, or at BEST be a Beta tester for a small experimental unit, 24-7-365 !

Have you googled Dragonheaters.com? Have you done a google search here in Permies for the Shippable core business Rocket Forum Thread stared by Paul W. About a
week ago ?

Think like Fire, Flow like Gas, Don't be the marshmallow ! As Always your Comments, and Questions are solicited and Welcome, and will be mostly answered ! Big AL

Hi Al thanks,
I haven't read the whole shippable core thread, perhaps I should, it didnt immidiatly seem relavent to my research but now I think about discussions about manufacturing ma well be interesting and enlightening.

Dragon Heaters I was on top of but thanks anyway.
They look nice and have clearly had some considerable research done on them but cost !! WOW

Let me make a promise ...
If I get this stuff to work as well as I suspect it might I will publish all plans and experimental date free along with credits for all contributors.
It's all about the planet not me and I earn enough to be comfortable.

I find it most interesting that the burn tunnel in the Dragon is cast and they have still retained a brick, well board, riser.
I cant help thinking that there must be a very good reason for that as the attention to detail is clearly very high, heading such exemplar warnings would be wise me thinks.

Insulating the top?
Actually it is all insulation but I anticipate needing something extra right above the riser to 'spread the heat out'.
OK I know, actually I will be dropping the pressure, cooling and slowing the gas a little, before it hits the heat exchangers but still I think the top will be vulnerable to erosion.

Anyway that's me for today, unfortunately I have to work, real work. I promised myself I would start at 10 and I am now late which is a neat trick when working from home.
laters folks ...

A2A : I am only repeating what I have been told here, and have no sources for Citation- But I have been told the Oldest barrel on any Rocket stoveMass Heater is
25 years, and that there are out there many models in the 15 - 20 yr range with their original Barrels, a few barrels have been replaced by Cautious home owners
to protect and preserve their Dragon's Lair, but no known reports of catastrophic failure !

This compares very favorably with the Warrantee you will get with a new, Fossil Fuel Fired Furnace Heat Exchanger! (air to air ) Though it would be fair to mention
to that most new heat exchangers are made of lighter steel than many of the 55 Gallon Drums out there !

For the Good of the Craft ! Think like Fire! Flo like Gas, Don't be the Marshmallow ! Your Comments, Questions, are solicited and Welcome ! Big AL

That is far more longevity than I imagined and is good to know, thanks Al

Hy Alistair. My English is poor and your text is to long for me LOL.. but how I uderstand what you need I dare to recomand ....
http://www.traditionaloven.com/articles/101/what-is-fire-clay-and-where-to-get-it here is one.
The amount of water from a heat exchanger usualy is approx. one third from the all amount of water in an installation for heating and hot water.This is important for your heat exchanger coils dimensions.
About thermosiphoning...if you are not using a pump ,in the circuit,than you need to use large diameter tubes let say 3\4 tzoll because of the friction and the heat exchanger have to be in a lower position like all the rest...and don't forget the coils ,I sure is about copper tube and is not 3\4 so I am sure you will need a pump.
I have a simple rocket stove ,for cooking and I use ash for insulation.
I hope I wasn't offtopic LOL
Please excuse my English ,is all I have and I hope is understandable for you.

Bump! A.L.