Are you interested in building a rocket mass heater? What is holding you back?

Daniel,

For #1 you can use a heat loss calculator to determine the heater size.
For #2 there is not much work-around. It takes time: planning, collecting materials, more planning and building.

Sophie - this forum is designed with all posts sequential, not responses grouped under individual posts. The idea is to always be able to see the latest post and not miss a new answer to a previous question. Threads should be limited to one basic topic so different conversations don't get tangled together.

Daniel - As mentioned, you can find heating requirement calculators online. Once you have a number, batchrocket.eu has information on system sizing for the requirements, for batch box designs. J-tube designs need to be scaled as mentioned above, with an 8" J-tube being similar to a 6" batch box. When you do have a system size determined, all the chamber proportions are determined by that, and described in numerous sources including batchrocket.eu. In general, oversizing a system a bit only means that you need to run it less often; if you undersize the system a bit, you need to run it more times a day in extreme weather which may be inconvenient. Greatly undersizing can be a real problem.

Self-feeding experiments have been done by many people, but they are all experiments. I would not advise trying to do such things in a system you want to just work out of the box. Also, self-feeding implies continuous or long-term burning, which is not required by the concept of a fast, hot fire that heats a mass for continuous gentle heating.  I recommend you go with mainstream designs, and with a bell or stratification chamber rather than piped mass, to make your build as reliable as possible. To be clear, if you do not have unusual conditions, recent common designs can be expected to work reliably if followed. As far as specific layout, proportions and surfaces of your installation, those can be tailored to your situation as long as you follow the basic technical rules.

Daniel Andy wrote:I'm also in the category of people who have thought about building an RMH and been turned off.  I'll cite two reasons, but insurance and materials are not them.

1) Design - I haven't seen a clear way to copy a safe design without first understanding why it needs to be done each way, and that leads to a rabbit hole of stove design expertise that I don't have the time to study.  Specifically, I want to be able to put in something like the square footage to be heated, the outer temperature, and the R value of the walls...and have something spit out a set of size constraints for the various chambers that will work.  I worry that by copying what others have built i'll end up with something either massively too big or (worse) too small for heating my space.  Then there's all the variations in the design. Such as do I go with a self-feeding design or not? I don't know and i lack the time to study enough to find out.

2) Time - Related to #1, but even if I had a turnkey design, I doubt I would have the time to spend building one, and I would be willing to pay to have it pre-built as much as possible.  Building an RMH while in the process of also building a roof and walls leads to a conflict in priorities. The roof and walls and foundation are going to win just about every time you have a moment to build something, so the RMH won't get built but a store-bought stove might go in during an hour or three, letting you go back to keeping dry.

Reduced time spent chopping wood is great, but I'm still at the point of designing the roof of my house, and I feel like I'll have to put off becoming efficient until after I can handle the basics.

Daniel, As post evolve, the themes take several directions.  with your two points, I will asnswer #1 first.

For the most part, the RMH designs protray what works. thus this method is laid out rather nicely on many fronts. and only when the design strays from "what works"  does the thread turns to what doesn't work. It would seem to put into all baskets the items that WORK, not spending much time on exactly why they work. certainly not  concentrating on all the things that don't work.

The basic RMH forums have proven, that if someone's plans are laid out for all to see, problems can be talked about, solutions made or suggested. And all goes well.  As for sizing requirements, only if you get far to small, do any promlems show.  The beauty of Mass, is the ability to burn a few times more vs less to control the amount of heat required.

#2-  Time, again, if looking for a reason not to, many reasons can be found,  as well as if your looking for reasons to do it. Also many reasons can be often found that a few extra hours can be hugely rewarded.    i.e.  $15,000 stone mason expense for labor and material vs $1000  for equal results done by home owner.  Everyone has their priorities. The beauty lies in the fact WE the HOMEOWNER can choose.

The "how to's" can be found.
The cost can be calculated.
The physical abilities have to be decided by the builder.   Not for everyone, but certainly do-able for many.

Best of success.

OK, so...  I would love a rocket stove but:

a) I am in doubt as to whether or not it can easily and sufficiently heat a large, high ceiling stone barn. This barn has a floor surface of 100 square metres (about 1070 square ft) and the height of the ceiling is 7 metres (23 ft) at the apex.  I am under the maybe wrong impression that a rocket stove is more suited for smaller spaces.  Also worried about how quickly it could heat that space after a couple of days away when the stone walls have seriously cooled down.  Humidity is also a big factor where I live.

b) We are both too old to build it ourselves and here in France, I have not found a reliable company that I would trust to build it for us.

c) I haven't quite come to the idea of an oil barrel sticking out from the corner of my living room, but I'm sure some designs would take care of this.

Hi Olga;
Let me ask you a few questions, and then I will address your concerns.

How are you heating your home now?  Wood? Electric? Gas?
Does your high-ceiling home have ceiling fans?
How often do you leave for a few days during heating season?  How cold is your winter season?

On to your concerns.
A) The latest designs of RMH Batchboxes no longer use an oil barrel; they are now built entirely of masonry.
Once warm, heating a high-ceilinged, open-floor-plan would be no problem.
Yes, masonry takes several hours from stone cold before it starts sharing its heat.
Your stone walls (as you know) are heat sinks; if they get cold, it's going to take time to heat them up, no matter what form of heating you use.
Humidity is not an issue with a wood burner.
B) If I may ask, how old is too old to build yourself?  Or perhaps a physical limitation would prevent you?  Both very valid reasons!
Despite common perceptions, building a clay/brick RMH isn't technically difficult; it can be built very slowly over many months.
Another option, have a younger person build one slowly under your supervision.
C)  The oil barrel is only a good idea if instant heat is desired; it is very easy to make your home too hot with one.
An all-masonry RMH can be built as a single skin or with a double skin.
The single skin takes several hours to warm up, and shares that heat for 12-24 hours.
A double skin takes twice as long to share its heat but can hold that heat 24-48 hrs.

I cannot describe how warm your home would be; you have to experience it for yourself.
But depending on how you heat now, once you heat with bricks, you will never go back.

thomas rubino wrote:...
B) If I may ask, how old is too old to build yourself?  Or perhaps a physical limitation would prevent you?  Both very valid reasons!
Despite common perceptions, building a clay/brick RMH isn't technically difficult; it can be built very slowly over many months.

My understanding is that Batchboxes are built with bricks and fireclay slip to hold the bricks together. So as Thomas suggests, you can build it one brick at a time - no mixing or pouring concrete.

That said, the base will require kneeling. Have you read any of this extremely long thread? https://permies.com/t/146023/aging-homesteader It is full of ideas of how to age in place by finding work-arounds for strength and mobility problems.

Thank you Thomas and Jay for your replies.

Thomas,
1) We heat ourselves with a wood burning stove.  We have a Norwegian Jotul FS 175.
https://intl.jotul.com/products/wood/wood-fireplaces/jotul-fs-175
Very efficient but consumes a fair amount of wood.
2) Yes we have a large ceiling fan
3) We do not leave our home willingly and not very often, but when it has happened, as you know, it takes a couple of days to heat the stone walls again and it's hard to get the room to temperature during that period, so wandering if RMH could deal with this
4) A few years ago, I would have said that our weather was hot summers and cold-ish winters (-8C to -10C), mostly mediterranean. However, the last 3 or 4 years has been very hot (42C to 44C) with long drought periods in the summers, followed by exceptionally wet winters and springs. Relentless rain causing our seasonal creek to overflow and cover our fields and orchard with 50cm deep fast running water for 6 to 8 weeks  at the time.  Temperatures can still go down to -10C.  We also have a micro climate as we live in a deep, bowl shaped land, subject to colder and damper weather than the immediate surrounding area.  It tends to attract mist and fog
5)  I know that humidity is not a problem for a woodburner.  I meant dampness. You see, in French, humidity and dampness is the same word (humidité) and I accidentally used the wrong word.  Our problem is dampness.  One, because of the above mentioned conditions but also because the house is built on a hill and part of the back wall is buried in the ground.  The region I live in is notorious for it's lime stones, hence all the old houses are built with what was then the available materials.  Unfortunately, lime stones are porous and absorb water fairly easily, so dampness is a big problem here
6) I could come round the idea of a barrel if you say that it would give a more instant heat

Jay,
Thank you for your reply and the link you have sent.  I did read through most of that thread at the time and even contributed to it.  Maybe saying that we were too old was the wrong statement, I am not defeated by my age and I am still putting on a full day's work regardless of my physical limitations.   Maybe it is just a mental adjustment that is needed.  It seems to be, to me at any rate, such a monumental change and upheaval to our already busy life, that I feel there is a lot to take into consideration.  Getting old to me means taking a bit longer to weigh the pros and cons.  Also, time is no longer on your side as you get older and priorities shift.  I'm ready to be convinced that this is a priority!

Olga Booker wrote: Getting old to me means taking a bit longer to weigh the pros and cons.  Also, time is no longer on your side as you get older and priorities shift.  I'm ready to be convinced that this is a priority!

Some famous US'ian said, "Getting old is not for wimps!"  I totally agree (it may have been Dolly Parton, but no guarantees)

I also totally understand your worries about whether the time and effort will have good results. From following some of the builds here on permies, the reduction in the amount of wood required to keep the house a comfortable temperature, seems like a major win for elderly home owners (I know - I'm in a crappy house with a wood stove and a hubby who's been gone for 6 weeks - but I can't convince him to take the alternative seriously.)

We are already at the point where a serious discussion about our priorities is overdue. I feel strongly we're spending too much of our time on tasks that aren't improving our quality of life, nor are prioritizing some of the "fun" things. Yes, there are people who, like you, are active and productive in their '80's, but I lost my sister to a sudden illness last year, and she hadn't turned 70. Two cousins very close to my age, were near misses. So yes, weigh those pros and cons, but much of what I've read about RMH's of all forms, including the ones that look more like masonry heaters, definitely make me lean towards them as improving ones quality of life.

If you return from a trip to a cold house, at least sitting right beside the "charging up" RMH, will get you warm. Having a few panels you can move to an area to create a "warm microclimate" with a small table and chairs to eat at, could help a lot with the cold issue during the reheating the house walls process.

If you do take the plunge, I'm sure you'll get a lot of support with ideas and methods and trouble shooting as you go - you will *not* be alone!

Olga Booker wrote:a) I am in doubt as to whether or not it can easily and sufficiently heat a large, high ceiling stone barn. This barn has a floor surface of 100 square metres (about 1070 square ft) and the height of the ceiling is 7 metres (23 ft) at the apex.  I am under the maybe wrong impression that a rocket stove is more suited for smaller spaces.  Also worried about how quickly it could heat that space after a couple of days away when the stone walls have seriously cooled down.

A high ceiling isn't a problem for a pure mass heater, most heat is coming off the walls as radiation. So, there's a relatively low amount of hot air in the shape of convection produced. A large batchrocket is a very potent space heater, have a look at this massive one, which is heating a space of 320 m² (3440 sq ft) with a 4+ m (13.1 ft) high ceiling, very little to no insulation at all in the building. The radiation of this biggie can be felt at a distance of 15 m (49.2 ft) across the entire shop space. Just an example, this heater is loaded three times in succesion 6 days a week. Won't cool down during the nights, so the shop space will be still quite warm in de mornings.
I won't say this the one for you, but it illustrates what is possible with a carefully made design.

Olga Booker wrote:b) We are both too old to build it ourselves and here in France, I have not found a reliable company that I would trust to build it for us.

It's all planning and gathering materials. The work itself can be spread out for many weeks, months even. There are examples of people, like Glenn Littman, who did one layer of bricks each day between coffee time and lunch, while probably having a power nap in the afternoon. It did give other people lots of time to be in time with comments and tips.

Olga Booker wrote:c) I haven't quite come to the idea of an oil barrel sticking out from the corner of my living room, but I'm sure some designs would take care of this.

As has been said by others, an oil barrel is not a necessaty. The whole of the heater could be masonry, and would even look beautiful when been plastered by a professional.

Thank you Jay for your lovely reply.  You are absolutely right,  Getting old is not for wimps!  whoever said it, I totally agree.

So sorry to hear about your sister, indeed, 70 these days is not that old.  I understand as I nearly lost my daughter this winter past and as I write, my brother in law is not going to make it back home from the hospital.  So yes, priorities shift and what seemed so important one day does not look so much so today.

I also have a husband that needs convincing.  Not that he doesn't like the idea of a RMH, it's just that he seems to see problems before they appear and talking him into something like this big, is more tiring than shovelling shit or even splitting wood!  I'm not giving up on the task just yet but a recent bout of Covid has put paid to my energy reserve for the time being!

If you return from a trip to a cold house, at least sitting right beside the "charging up" RMH, will get you warm

That was my main concern, how quickly can you feel some heat when you come back to an unheated, empty house.  From what you are saying, it seems pretty quick?

Anyway, I'm sure we'll get round to it at some point, and it's nice to know as you've said, that I'm not alone.

Thank you Peter, food for thoughts indeed.  I like the idea of radiating heat and will look at some more RMH designs.

I built a metal access panel into the front of my RMH bell, and it gives a decent amount of instant heat while waiting for the stored heat to work its way through the massive bell walls. It also allows clear access to inspect and clean the riser and interior of the bell.

The 7" square glass pane on my Shorty Core quickly throws an amazing amount of heat.
The door metal itself also quickly becomes a radiator.
If you choose to build a high-mass stove, your wood needs will plummet, and your home will be toasty warm from front to back.

Olga Booker wrote:Thank you Thomas and Jay for your replies.

Thomas,
1) We heat ourselves with a wood burning stove.  We have a Norwegian Jotul FS 175.
https://intl.jotul.com/products/wood/wood-fireplaces/jotul-fs-175
Very efficient but consumes a fair amount of wood.

I just want to point out the conflicting wording to those that assume  they go hand in hand.

ALL wood has a certain BTU value per weight of wood. surprisingly this value based on weight of the dry wood, is relatively close range,  i.e.  btu's per given weight for softwoods is not that much different for the same given weight for some of the hardwoods.

Thus if you burn a "fair amount of wood" and both stoves your comparing are effcient, then the BTU's produced will be close to the same.

HOW the heat is stored, dispersed, and utilized, is the difference of two different but very efficient stoves. One will not PRODUCE more heat per given weight of wood than the other. This area has been confused for years.

  But when comparing a inefficient stove that has a smoldering mode, to a RMH, that burns clean and always does so, and then effciently collects and distrubutes the heat is when things get far apart for your efforts in collecting the wood to burn.

Hope this helps!

Thomas and Glen, thank you for that bit of information, it helps me to think more positively about an RMH,  Would it be too much trouble to ask for a photo??

Hi Olga;
Here you go.
Shorty core is a single skin
The Studio dragon is a double skin, first-generation Batchbox.
My shop dragon is a unique hybrid, a first-generation Batchbox using double barrels and a single-skin bell.

Thanks Thomas!

Here is a photo of the first fire in my RMH. I have removed the access panel for inspection and cleaning twice in about 9 years. The oven/cooktop insert didn't work so well for those purposes, but it does radiate a noticeable amount of heat as well.
https://permies.com/t/60784/a/45569/IMG_1338-w600.jpg

Thanks Glenn, great photos.

Here is what i'm thinking of. The kitchen/dining/living is open, so I'm looking at placing the heater in the middle...in the living area...against the wall. In the basement, I'll put the elevator shaft-like support that was described. I'd like to have openings in the walls to allow heat/air to circulate...above the doors.  The program I'm using makes it tricky (at least for me) to see what's happening, wall-wise, because it shows the basement and main floor walls at the same time, so one picture is of that and the other is less detailed of the main floor.

I'm not attached to any of the design/layout, except it having a walk-out basement. My ideal is to have the masonry heater, water catchment system to supply most, if not all, my water, and a vermicomposting toilet situation. I'm very open to all suggestions and critique.

Thanks in advance.

So, after doing some math and counting my pennies, I've redone the plans and will repost asap. Where the heater will be located hasn't changed...it will be against the closets wall and in the open kitchen/dining area. I plan to get the support in the basement built and the roof ready to receive it. I'll work on building the unit once i'm in and use an alt heat source in the meantime.

Hi everyone,

As I still think this is one of the best threads on this forum, I want to add one more resource to the conversation.

Every once in a while, a video comes along that provides an excellent overview of rocket mass heaters from all angles. The video below focuses on the general concept rather than the exact details of a single type. Since everyone has to start somewhere, understanding the ultimate goal is a great first step if you are considering building one.



Although this video is older, the information remains highly relevant. It lays out many important facts that can be difficult to explain in writing.

I highly recommend taking a look. The only major hurdle the video doesn't have an answer for is navigating local regulations and bureaucratic restrictions if you live in an area that strictly enforces them.

Best regards,

Scott Weinberg

--
Scott- Iron Design L.L.C.
Scott Weinberg

I'm getting ready for a RMH build in my cabin here in southern Ohio. I've been shopping for used firebrick and stove pipe. I'm planning on doing an 8 inch J-tube with a cob bench. I've considered a batch box but like the simplicity of the J-tube. I've used a RMH before when I lived in Oregon. I built a really nice Rocket oven 6 years ago and it has been awesome and is still doing good... The RMH will have a firebrick core with an insulated riser and 55 gallon barrel. I'm leaning toward running about 20 feet of stove pipe through a cob bench but I'm also thinking about a half barrel stratification chamber covered with cob.....Here's a few questions I have..... I can get a stainless steel barrel for $100 which is really cheap. I love the immediate heat from the riser barrel but I'm wondering if the stainless steel barrel will radiate less heat than a typical carbon steel barrel? I know it will last longer but I'm thinking that more heat will go into the bench with stainless steel....One other question....Typical 22 gauge 8 inch stove pipe is .030 - .032 inches or .762mm - .81mm thick. The 18 gauge half barrel that I will use is .039 - .047 inches or 1mm - 1.2mm thick. The half barrel is a little thicker than the stove pipe. Will that make much of a difference? Will the thinner stove pipe transfer more heat to the cob bench and transfer it faster? It seems to me that the thinner stove pipe would be a little more efficient transferring the heat.

Hi Joe;
A quick reply.
A stainless barrel is used for looks only.
Heat radiation is comparable to steel; you will not gain or lose anything.

Using a piped mass is no longer recommended; they need cleaning, and the solid mass adds unnecessary weight.
Stratification chambers can be any shape or size that fits your needs and space.
An 8" J-Tube uses the ISA numbers for a 6" Batchbox

Thanks for the response Thomas.

The stainless will definitely last longer. I can get carbon steel barrels for free or $10 where I'm at though. Removing the paint can be a job. I'm probably not going to spend up for the stainless.

I think I'm over analyzing the thickness difference between the stove pipe and half barrel. Probably not that much difference in heat transfer and efficiency. I've been shopping for stove pipe and it's not cheap. The half barrels will definitely be cheaper. I'm leaning toward the stratification chamber. I'll let you know how the build goes.

One question for you THomas.

If I don't care about the height of the cob bench would using full 55 gallon barrels work in the stratification chamber? I would cover the barrels with about 5 inches of cob. I saw a video here where Paul used full barrels in a pebble style bench.

I've thought about pebble style but like the better efficiency of cob and I have lots of clay on my property.

Hey Joe;   I still have the  barrel I bought in 2013 for my first RMH.
It is off to the side and out of service now, but it was in seasonal use until 2025.
It could be installed today and put back in service.  They do not wear out.

Can you use full barrels rather than split ones?  Sure I guess so.
Although the extra-thick cob at the bottom would not heat up, the thinner side covering would.

Paint removal is not bad at all if you are in a location where a wood waste burn barrel is allowed.
With one good burn, 2/3 of the paint will be gone; then you burn a small fire and leave the barrel tipped on its side, rolling it as the paint comes off.

So, I've been thinking about an RMH for what?  10 years now?  Bought the books, bought the videos, etc, etc,.   I just turned 80, but I'm still game for doing this!  I cut my own trees, build my own hedges, grow more and more of my own food.  But I'm trying to cut the labor for the daily necessities, so I don't have to move to a simpler place until I'm well into my 90's, and maybe even 100.  I want to age in place, allowing myself to become more cantankerous and irascible as I go!


The problem is the rest of the house.  Everything in the literature here and elsewhere emphasizes that RMHs heat by radiation!  The only place I can put one of these things -- no matter how good looking it is -- is in the cellar!  We have a big woodstove there now, with insulated stainless steel chimney up past the roof peak.  It's an old stone cellar that I'm almost finished repointing to stop the leaks when it rains.  And then I plan to build a wall to hold insulation and reflective metal between the stove heat and the 50 degree stone work -- heat moves to the largest temp difference - I'd rather have the heat go up!

But that still leaves the amount of wood!  We burn about 20 face cords a season; some I cut from the woodlot, but I had a quad bypass 5 years ago and most of those years we had to buy.  The price is now over $85/FC and this is getting ridiculous!  This year I'm cutting more of my own, but I'm clear about the effects of aging.  Who knows how long I'll be able to take down treea and cut them up.  So one of the solutions is to coppice black locust.  I've got the land to do that, and in 3-5 years, I should no long need to split wood; just wait for the locust to dry in 4-5" billets and burn that.  Less work and more heat from the wood!

Now: I very much WANT to build an RMH!  And I'm absolutely in love with the new Batchbox designs!  And mortaring brick is easily within my skill level and physical ability.  

What's stopping me is the lack of attention to how to move heat for PEOPLE WHO DO NOT LIVE IN OPEN SPACE LIVING ARRANGEMENTS.  Many warnings not to try to use a heat exchanger because the water with explode!  But that's not always true.  There must be ways to arrange the pipes where the heat will stay safely below 200 degrees...  Or how about an air exchanger ported into my existing ductwork?   I have to think of these things myself..

My hunch is that the reason most people aren't building these is because most people live in "conventional" housing and all the experts are telling us this won't work there.  

Wood is the cheapest dense form of heat there is.  I've been considering solar electric or parabolic trough collector with sand batteries (heat up to 500 degrees in the sand!) and taking hot water off the top of that (and building a Stirling engine to make electricity when the sun isn't shining...)  But wood around me is still easy to get or grow.  And the BTUs per cord are astonishing!  Most of that goes up the chimney now.  But to be able to keep that heat in the house and distribute it somehow to the upstairs rooms (drain back thermosyphon or pump to floor radiators or old radiators?  from a hot water tank in the cellar?) -- that would be like heaven!  And to have that with two loads a day!  

So, a little more on the "back end" as Peter van den Berg calls it would help.  Is there anyone else out there trying to deal with this issue?

Thanks for any help or advice you can offer!
Gary

Gary Throop wrote:

The problem is the rest of the house.  Everything in the literature here and elsewhere emphasizes that RMHs heat by radiation!  The only place I can put one of these things -- no matter how good looking it is -- is in the cellar!  We have a big woodstove there now, with insulated stainless steel chimney up past the roof peak.  It's an old stone cellar that I'm almost finished repointing to stop the leaks when it rains.  And then I plan to build a wall to hold insulation and reflective metal between the stove heat and the 50 degree stone work -- heat moves to the largest temp difference - I'd rather have the heat go up!

Gary you have tossed out several thoughts and that is good, and I will try to tackle a few as we have similarities
I have a very large house with NO options for stove on any of the main floors in any location, thus am in the basement as you describe and most likely for the same reasons. So with that in mind, exactly as you were thinking if you have this huge base within 20 foot of your stove that is 50 degrees (basement walls) that is a obstical for sure. and your insulated walls in my opinion would be the correct way to go. Thus the heat will work its way up?  But you are getting around this now by simply burning a lot of wood?

Gary Throop wrote:
But that still leaves the amount of wood!  We burn about 20 face cords a season; some I cut from the woodlot, but I had a quad bypass 5 years ago and most of those years we had to buy.  The price is now over $85/FC and this is getting ridiculous!  This year I'm cutting more of my own, but I'm clear about the effects of aging.  Who knows how long I'll be able to take down treea and cut them up.  So one of the solutions is to coppice black locust.  I've got the land to do that, and in 3-5 years, I should no long need to split wood; just wait for the locust to dry in 4-5" billets and burn that.  Less work and more heat from the wood!

So yes, it would appear that shear volume of wood burning has been in order?  While your going to get more heat for same volume of wood, that does not mean it is going to work better, just less wood used.  How you get the wood, I think in this case does not answer anything about what to do with the wood heat from your stove and how to handle it.

Gary Throop wrote:

What's stopping me is the lack of attention to how to move heat for PEOPLE WHO DO NOT LIVE IN OPEN SPACE LIVING ARRANGEMENTS.  Many warnings not to try to use a heat exchanger because the water with explode!  But that's not always true.  There must be ways to arrange the pipes where the heat will stay safely below 200 degrees...  Or how about an air exchanger ported into my existing ductwork?   I have to think of these things myself..

My hunch is that the reason most people aren't building these is because most people live in "conventional" housing and all the experts are telling us this won't work there.  

 A lot of things going on with some of your thinking, and in various locations on the forum, much has been discussed, but if you can indulge me a bit
1) Almost all warnings about steam explosions have to do with those that are wanting to build a closed system without all of the required pop off valves or system shutdown devices.  You wouldn't build a boiler/steam set up with out those safety things, yet almost always when the warning flyout if is for this very reason.
2) And yes you can certainly go bigger or more volume of water to where it simply can't get over 200 degrees, but ..............if we are trying to heat with the wood (the water) and have the water heat us?   you can see where I am going with this. Pretty soon our simple RMH is no longer simple and I have to give this forum credit,  ( The basic RMH is relatively simple )
3)  So you have ductwork? with a fan?  I have for years warmed my Bell and circulated the heat. Not ideal radiation methode but the basement does become a nice place to be.

Gary Throop wrote:
Wood is the cheapest dense form of heat there is.  I've been considering solar electric or parabolic trough collector with sand batteries (heat up to 500 degrees in the sand!) and taking hot water off the top of that (and building a Stirling engine to make electricity when the sun isn't shining...)  But wood around me is still easy to get or grow.  And the BTUs per cord are astonishing!  Most of that goes up the chimney now.  But to be able to keep that heat in the house and distribute it somehow to the upstairs rooms (drain back thermosyphon or pump to floor radiators or old radiators?  from a hot water tank in the cellar?) -- that would be like heaven!  And to have that with two loads a day!  

I am afraid that shotgun full of ideas makes it hard to advise on a direction you want to go.  But I will comment on a few
1) would love to know of anyone that has built a sand battery for a house that has even obtained 250 degrees let alone 500, if such temps were hit? HOW?
2) you started with a RMH idea, but are tossing in parabolic troughs, sand batteries, ( and by the way, if you truly thinking you can control water through a 500 degree sand battery, you will get a onslaught of WARNINGS from everyone and for good reason. This is not brick and mortor stuff.
3) well you can see where I am going with this,  are you wanting simple or complicated? Looks like you have all in mind.
4) Please don't get me wrong, I am not against any of your ideas, but feel it is all obtainable with enough money and skill through at it, that does not mean it is economical.

Gary Throop wrote:
So, a little more on the "back end" as Peter van den Berg calls it would help.  Is there anyone else out there trying to deal with this issue?

Thanks for any help or advice you can offer!
Gary

If you had to pick one thing, with your questions and statements, that you would most like advice on? what would it be?  Or simply my advice would be to choose simple or complex as there is not to much middle ground.   Best of success.

Thank you, Scott!  I appreciate the quick reply.  You're right - I'm chasing a lot of ideas.  I don't like to make a real investment of money and time and THEN discover it was an error!  I'm too old for that and don't have time to recover from dead losses...  So I'm spending a lot of energy exploring all those ideas.

I have essentially decide to build a batch box rocket and hopefully I can scrape together the money and time to do it this year.  I'm also building a Jean Pain pile between the barn and the chicken coop to heat water for the chix and horses this winter.  I am intimately familiar with wood and the same with wood chips and horse shit.  And I've done enough masonry to think I can pile bricks up with a good plan.  Building them is the realistic part.  Its the heat transfer that I still need some innovative thinking on...

Meanwhile, I'm also not giving up sand batteries and solar power.  It's just too simple: put the solar panel in the sun, point it south (okay, oversimplifying that just a bit...), run a wire into the cellar and hook it up to a metal heating ring or plug, whathaveyou embedded in the sand (behind insulation) and let 'er rip!  To move heat off it, again, is the problem.  Yes, water direct into/out of such a hot mass would be explosive and not at all advised.  But copper coil wrapping the insulation?  I dunno.  How hot would it be on the outside of the insulation?  How fast would the water be moving through the coil?  Same problem with the RMH bench: how hot DOES it get to be on the outside of the cob?  Just inside the cob?  How hot is it on the outside wall of a batch burner?  Cool enough to not boil the inside of a copper coil?  Could the copper coil be held in place at a small distance?  small enough to not boil?  I guess I get to experiment on that...

Thanks again!  And if anybody else is reading this and has some experience to share on transferring heat from ANY type of hot mass, I'd love to hear about it.

Gary

Okay.  Here's a simple one.  I've been reading up on all the batch box stuff and the term double skin keeps coming up.  But I haven't seen any illustrations of what that means...  Is it a core with two brick boxes built around it with an air gap between them?

Second: on my heat transfer question: someone wrote that the preferred exit temp at the bottom of the batch box on the way to the chimney is 120-200 degrees F.  That's just the right temp for a copper coil of water to transfer heat to a tank on the way to radiators in a thermosyphon.  BUT someone else said the chimney temp needs to stay north of 140 deg F.  Will sucking heat out with a coil drop the temp too much to heat the chimney and maintain the draw?

And if so, how about a coil wrapped out the outside wall of the box?  Does the outside wall get hot enough to boil water?  Would I need to exit the coil into an open to the air expansion tank to avoid explosions?  I'm trying to find a Goldilocks location in the heat flow that I can pull some heat out to send upstairs...

Thanks for any advice you can give.  This forum is EXTREMELY informative!

Gary

Oh, wow!  I just found this guy on YouTube!  A total inspiration!  He looks as old as I am and look what he did!  If he can do this, so can I!

Has anyone seen this?  Any comments?  Suggestions?  Criticisms?



Gary

Hey Gary, check out this double skin build
https://permies.com/t/360535/Build-Generation-Batchbox-Double-Brick

Hey Gary;
Carl is a poster here at permies
https://permies.com/t/225438/Critique-Design

Gary Throop wrote:Oh, wow!  I just found this guy on YouTube!  A total inspiration!  He looks as old as I am and look what he did!  If he can do this, so can I!

Has anyone seen this?  Any comments?  Suggestions?  Criticisms?

Gary

While we will probably never know, I would like to know what the ISA is/was and size of stove itself  5"-6" or 7" and this would give a correlation number that we know today because of Peters work, that really works well.  Who knows, this build might have been spot on.  

On a side note, those kinds of bricks with the holes, can be or should be filled, as that is a mass gain of very little cost, and I am not talking about a sand filling, sand simply insulates far to much!

Over the years, I have changed my thoughts on good working stove and that is simply- "It should work for years and years with little maintenance"  Probably one of the biggest reasons that the simple bell, single or double has really took hold the world over.  It is a grand design, that is easy to predict, easy to build, and works well for years.