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.