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RMH cook stove in small home...

 
Posts: 66
Location: South Central Alaska Zone 4a/b
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Hello,
I have asked some vague questions on RMH stuff before, but our plans are evolving and slowly solidifying, so I have some more detailed questions now...

We live in South Central Alaska. Grow Zone 4a/b. Lots of precip, wet climate. Coldest temps -30F or so. Warmest 90F, but its rare. 70's are often as warm as it gets.

Our current plan is to buy a small piece of land and build a 300-400sqft house. Currently we are exploring using SIP's. They have their pros and cons... I do not like how many synthetic petroleum based products they use, and I am concerned about off gassing. But they will allow us to construct the house with a couple of people in a weekend or so (a necessary piece if this is going to happen at all, because we can't pay someone to build it, and my husband has a rigorous work schedule in the summer months), and are very affordable from a local(ish) company. (If anyone has a suggestion of a more natural option that can be built quickly and cheaply, and withstands a wet and cold climate well, I'm all ears) Anyway, that means this 300-400sqft house would have roughly R-40 walls!

My plan has always been to heat the home, cook/bake/smoke the food, and heat the water with an RMH. I am concerned about getting utterly blown out with R-40 walls, in such a small space. In the past I was sure I would use either Matt Walker's tiny cook stove, or full masonry cook stove depending on the size of the home we built. Now with an even smaller foot print, and higher insulation, I'm wondering if we need to change course...?

I also just came across this from Glen Herbert on an old thread:

"A J-tube needs to be fed every 5-15 minutes or so depending on the size of the wood, but you can stop whenever you feel you have put enough heat into the system. A batch box is supposed to be loaded full or it will not run efficiently, and you can't really stop it until it is finished its hour or so burn. The batch box tends to put more heat into the system faster. So your living patterns will influence the best setup for you. If you want to tend and cook on it every day, you probably want a J-tube"

1) I intend to cook on this stove. At this point I do not have an alternative indoor cooking option in the house plans (they could be added if necessary, but I haven't explored it yet.) Should I consider a J-tube instead of the batch style?
2) Should I NOT build a bench, and just do a masonry bell with stovetop, oven, H20 heat exchanger?
3) We have lots of clay in our area, and beach sand. Can a bell be build from cob, or does it need an internal structure of masonry? What about homemade unfired bricks and cob over top? I have never used cob and I'm still trying to wrap my head around what it can and cannot do...
4) There is also a lot of stones at the beach, most of them round and smooth, and some more square. How does stone do for a bell?

I should also note, that we intend to do outdoor cooking routinely in the summer time, and I do not mind opening windows if we need to be inside. Highs in the summer here are generally around 70F, though the sunshine is intense, and I intend to put plenty of S facing windows in the house for light (and heat, but mostly light) in the winter months.

What would you do in this situation?

Sometimes I am not graceful in articulating my questions in a way that is clear to the reader, so please ask any necessary clarifying questions and I'll do my best to respond. Internet communication is still not my favorite mode, but I have found Permies super helpful, so I will to make time to get back on and respond!
 
pollinator
Posts: 5159
Location: Bendigo , Australia
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Are you concerned the house will get too hot?
Have you studied the use of SIP homes and got an understanding of them?
Can you speak with people living in them?
I assume its a 'summer' house for weekends etc, have you considered LPG cooking?
Perhaps look at this;
https://www.houzz.com/discussions/2269739/anyone-live-in-a-sip-home
 
Eloise Rock
Posts: 66
Location: South Central Alaska Zone 4a/b
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Another question

I know I need to read up more on technical aspects before attempting any builds. Given my scenario, what resource would you recommend? I know of the Evans book, Erica & Ernie's book, the Donkey forums... I have only looked at the donkey forums a time or two, and found them over my head. So maybe I need a book first?
 
gardener
Posts: 1769
Location: Kingman, Arizona
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Eloise Rock wrote:If anyone has a suggestion of a more natural option that can be built quickly and cheaply, and withstands a wet and cold climate well, I'm all ears.


Generally quickly and cheaply don't go together when constructing a natural house. They are often a labour of love that ends up taking a long time to build, but the end result is often well worth it. For instance, earth bag houses are often quoted as being 'dirt' cheap, but if you've ever built one, it takes a lot of labour and time to make progress. Is there an option to live in a temporary house while you build your dream home?


In the past I was sure I would use either Matt Walker's tiny cook stove, or full masonry cook stove depending on the size of the home we built. Now with an even smaller foot print, and higher insulation, I'm wondering if we need to change course...?


I think Matt's tiny cook stove is a great option. Being multifuncional as a heating source and cook stove, IMO its footprint is well justified. A bypass is certainly not something you'd want to leave out as it can direct the heat outside faster if the inside is already warm enough.

1)Should I consider a J-tube instead of the batch style?


If you didn't go with Matt's stove then I probably would start there. Glenn makes some good points pro J for your situation.

2) Should I NOT build a bench, and just do a masonry bell with stovetop, oven, H20 heat exchanger?


A bench can be great to sit on to warm up, dry stuff, act as a warming bed for plants, yogurt, sourdough etc. but if your not interested in these things, it can take up valuable floor space in a tiny home. A tower bell takes up much less room yet still provides the thermal mass to carry the heat much longer.  

3) We have lots of clay in our area, and beach sand. Can a bell be build from cob, or does it need an internal structure of masonry? What about homemade unfired bricks and cob over top? I have never used cob and I'm still trying to wrap my head around what it can and cannot do...


Beach sand is roundish and not so great for making cob with. Sharp angular sand is preferred to produce a stronger product.
The best thermal mass is made from dense, heavy non-combustible materials with just enough cob being saved for the mortar to hold it all together and as a skin to make it look pretty and smooth. Also great for roundish, artistic elements that you can customize exactly the way you like it. Also, if unfired cob is re-wetted, it can be used over and over again, adding or subtracting to meet your current needs.  

4) There is also a lot of stones at the beach, most of them round and smooth, and some more square. How does stone do for a bell?


Stone works great as a thermal mass. Squarish makes for easier stacking but round (especially when left exposed) can be very attractive.
 
Gerry Parent
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Posts: 1769
Location: Kingman, Arizona
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Eloise,   I found the The Hand Sculpted House by Ianto Evans has been a great go-to book that provides a good basis for all kinds of natural building.
 
rocket scientist
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Hi Eloise;
I had to look up what "sip's" buildings were!
It turns out that I had an intimate knowledge of them, and did not know it!
I spent the last 3 months, building two large metal buildings with the Ironworkers that were sided and roofed with Structural Insulated Panels!  Sip's who knew!
They are a very neat idea!  They work really slick, They go up fast with a crane.


Awesome that you're wanting an RMH in your new home.
With a smaller footprint and the super-insulated building, it will not take much to keep it warm.
An 8" J tube will burn for 45 minutes between loadings.
A 6" J tube might go 25 minutes or so.
A 6" batch box will burn 1.5 hrs and have coals longer.
A 6" walker cook stove will burn around 30 minutes between loading.
A propane cook stove and a summer kitchen outdoors are fine ideas, I have both myself.
A propane cooktop indoors is really nice for quick water heating.

Great you have plenty of clay and sand.
Try to need as little as possible of it!  Hard labor to create large amounts of cob.
It does make a fine mortar for sealing things.
Ocean rock will work fine as a mass however it should be insulated from the highest heat of the core
I suggest building Matt's tiny cook stove. It will have a cooktop and an oven.
Matt's stove can be built with an attached mass.
That mass can be bypassed for easy starting, cooking, and for less space heating.
A hollow mass can be built using split 55 gal. barrels. Called the Walker half-barrel system.
Bricks are commonly used as masonry bells but they might be hard to come by in AK.
A large metal tank surrounded by stone and with more stone inside makes a fine bell.

Using pipes and a solid mass is fast becoming an outdated method.

I live in the North Wet part of Montana.
35F and drizzling rain can be bone-chilling or rather nice depending on your activity level.
A warm wood stove is always a good thing! If it feels too hot, then that is what doors and windows have screens for!
At -30F you will want every inch of insulation you can get!







 
Eloise Rock
Posts: 66
Location: South Central Alaska Zone 4a/b
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Thanks all for your helpful responses! I will try to make the necessary clarifications here:


Yes, John, my concern is that we will be too hot with such a small footprint and high insulation value and awesomely hot stove, though Thomas seems to think it may not be a problem, which would be a relief! We have some friends here who just built their house with SIPs last summer and in their own words "are passionate about them". They put up their house in less than 4 days with 2 people if I remember right (its a two story, ~25x35ft or so). No crane used, just scaffolding. Honestly I had written SIP's off because of the potential for VOC's, but when they shared their experience I began to re-think...

This would be the stepping stone house to the dream house. Basically, we can't afford to save the money for the dream house while paying rent. So need to get into something we own. SIP's make that possible, especially if we do it small. Then save the dollars and learn the skills to do a more natural home. We are leaning toward log for that, as that's what has historically been done here, and the Land can provide the resources for it. We are not opposed to living in a temporary shelter (we have a canvas with a wood stove that we love), but if we lived in that while building a full scribe log cabin (which we have no experience with yet), I expect we would have to live in it a full year, which doesn't sound quite as romantic to me. That said if there was a more natural option that would fill this gap we'd certainly look into it. I am guessing there is just going to have to be a compromise made for this "stepping stone" portion of the journey.

Based on Thomas' response, I am thinking the Tiny Cook stove is still the way to go... I was worried that even that may have too much output and too much mass for a space that size, but I'd love it if that were not so, since I've long dreamed of having that stove in my home. Do you all think having a bench on that stove would still be comfortable (With a bypass)? Most of the floor plans I have drawn include a bench for all the reasons Gerry mentioned. In fact I'd really like to have a bench big enough to use as an extra sleeping space if someone comes to visit - long and wide enough to sleep on with out worrying about rolling off. Maybe 32-36" wide and 6.5ft? Would adding that much mass to a space that small be super overboard, keeping in mind I will be cooking on it consistently? I will also look into the Walker half barrel bench. I know I saw a video on that ages ago, but never investigated it more than that.

A part of the reason I asked about the clay and sand is because bricks are indeed harder to come by here than down south. We could save some significant cash (and logistics) by building the mass with stone or cob or something. Of course we have no experience with either of those either, so its weighing cost with what is doable to take on and learn all at once. I am a potter and familiar with clay in general, but using it to build something is different than making pretty mugs.

Thomas, how do you recommend insulating the stone from the highest heat of the core? I am picturing the core being made from Ceramic Fiber Board and building the stone bell around that (large air space between), with metal or glass stove top. Is the air space between the stone and CFB core sufficient? Or would the core need to be wrapped with something? Or stone cobbed over on the inside? What do you have in mind?

I know your weather well, Thomas, as I used to live in that area (and miss it dearly)! We also get lots of rain in the fall and spring here, so 35F and wet is an all too familiar experience, and I would much rather open a window (due to a too hot stove) than endure the chill those conditions create!

Final question: If we go with the Tiny Cook Stove, I intend to buy Matt's plans. Would either of the RMH Books be a worthwhile addition for that build? Or is the batch box design of the stove be different enough it won't really apply?

You all have been super helpful already! Thanks for the help!
-E
 
thomas rubino
rocket scientist
Posts: 5859
Location: latitude 47 N.W. montana zone 6A
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Hi E;
I guess I was working with industrial-size sips.
The wall panels were 42"x 26' tall and the roof panels were 42" wide and 53' long, they weighed over #600 each...

So let us start with the reading material.
Both books are full of good information and always worth reading!
A local library or bookmobile might get you copies to read during the winter.
Neither will help much with a Walker riserless core.
Matt's design is unique to his stoves.
Also with the popularity and convenience of using hollow bells rather than a piped mass, the information in those
books do not reflect the newest innovations.
Matt himself is your very best source of info on his builds.
After buying his plans you get unlimited email access to work out any questions you might have.
Of course, we here at Permies can offer help as well.  Some of us have built Matt's design and understand how it functions.

You mentioned that you are planning on using a CFB core and wondered about how close your stone can be.
The CFB has to have a solid backing. Ideally, it would butt against clay bricks.
Matt's plans are based on using clay brick but substituting stone, although harder to work with can be done.
With a square stone backing you would want a layer of cob mortar to make a solid connection.
The stones that are available, do you have any idea what kind of rock they are?
Stones with trapped water can crack with heat.
Outside of a CFB core the temps should be acceptable to use the large square stones with a mortar face.
Any part of the mass can be stone as mass temps are in the 100-300F range.
Were you planning on using clay bricks for the Walker at all? Or were you hoping to use all stone?

Yes, you could have a half-barrel bench large enough to be a comfy bed.

Also, are you planning on using an RA330 liner for your CFB core?
CFB is very susceptible to abrasion. Without a liner, wood must be very carefully loaded to avoid gouging.









 
Eloise Rock
Posts: 66
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Thanks Thomas,

Those panels sound huge! The ones this company makes for residential use are 4x8 to 4x12 ft I think.

Sounds like Matt will be an important resource for this. I am not set on using or not using any specific materials at this point. Just exploring options. I know bricks must be here somewhere, but I haven't found them yet haha... I can find pavers and cement block, but standard bricks are harder more difficult. I havent checked anchorage yet though. There are more options there. If we can find bricks with out breaking the bank, that would actually be my first choice, because in my mind it sounds easier to learn to lay bricks than irregular stones. Since there will already be lots of learning, no reason to make it harder than it has to be.

I am not familiar with an RA 330 Liner. I am not set on using CFB either. Do you prefer hard fire brick?
 
thomas rubino
rocket scientist
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Hi E;
I am not a fan of CFB anywhere it can be abraded.
I have tried it with J tube rockets and as roofs on numerous batch boxes, it has failed miserably every time.
However, away /protected from abrasion it is a fine insulator.

I am a fan of using heavy firebricks for cores.
My Walker BBQ uses the same riserless core that the tiny cook stove does.
I built it using heavy firebrick.   I love it!  However, it is not easy to start.
It can and does create clouds of smoke. As this is an outdoor stove I don't mind.
Once the core comes up to temp it burns clean and hot.
This can take 30 minutes or more.
By using a CFB core, there is very little warmup time. Your stove will rocket off quickly and burn cleanly.

RA330 is a high temp metal. Matt has a "liner" of it inside his firebox to protect the CFB from wood abrasion.
You can read all about it on my website https://dragontechrmh.com/
As your stove is inside, CFB with a liner might be a better choice.

If you can locate clay bricks, you only need enough for the tiny stove.
Your mass can be built with the local stone.


20211217_112039-(1).jpg
Walker Black and White oven
Walker Black and White oven
20210924_114850.jpg
Outdoor kitchen
Outdoor kitchen
 
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