Advice on a RMH build in Hokkaido Japan

Your thermometer looks perfect to me. I wouldn't worry about the epoxy. If the hole is made so its a tight fit, that should be good. If it doesn't want to stay there and fall out, then you can come up with something like a magnet or wire to hold it in place. The probe tends to build up with the 'black fuzz' after some time so its helpful to clean it maybe a few times a year to keep it more accurate.

Perhaps a bit late to mention but just thinking that the perlite your putting between the chimney pipes is going to settle after some time. Wondering if wrapping it with rock wool wouldn't be easier.

Hi Peter;
Normally a candy thermo is used.    Gerry and I call them the dragon breath monitor.  Mine has no threads so I just drilled a tight hole and forced it thru, with no sealer.
It gives a much more accurate indication of how well your dragon is burning.

Thomas and Gerry have replied for me!

Gerry Parent wrote:

Perhaps a bit late to mention but just thinking that the perlite your putting between the chimney pipes is going to settle after some time. Wondering if wrapping it with rock wool wouldn't be easier.

Perhaps:)

The Rockwool at the home center was $45 for half a meter. Need close to 8 meters. So I bought the perlite instead. Can alway check from the roof how much it’s settled and top up. Downside of the perlite is that it’s a pain in the ass if we need to move or adjust the chimney. I just assumed to perlite would be a good idea. However now that I think about it I have no idea what the actual insulation value of 2.5cm of lose perlite inside of spiral duct piping will be. Any thoughts? Is this a potential oversight on my part that may create a fire hazard? The ceiling in the room is just drywall. I’ve cut back any wooden parts away from the holes where the flue piping runs. What kind of temperature (Celsius/Fahrenheit) should we be expecting on the outside of our double run 2.5cm perlite insulated flue pipe and is there anything I should be concerned with prior to starting a test fire in the house? Staying warm is a top priority for us, but making educated decisions and being safe is the most important of all.

Cheers Peter

“Well I’m beginning to see the light...“ VU

I know I'm supposed to say something very knowledgeable, but right now all I can see is coming up with captions for your photos. The first one is "Mimi the Japanese Wolverine"
and the last one "Chimi 007".........OK feel better now......
As for an answer: I really have no idea how much is enough. The hillbilly way would be to go ahead with your plan and load er' up with the perlite, then put your hand on the pipe where it goes through the ceiling and see how hot it is. If you can't hold your hand there for more than a second, its probably way too hot. As you probably know they do sell metal insulated collars (for probably gobs of money) or you could make your own if you feel industrious. A detail that can be changed after you get some heat going and with some careful monitoring to see if extra is needed....like some of that extra CFB. The beauty of this kind of stove is that the exhaust is much cooler and therefore much safer than a regular wood stove, but I think I read in the RMH Manual that you also have to think of possible future occupants also. If they decide to undo all your work and put in a regular wood stove thinking the chimney is all set up for high heat use and burn the place down then that kinda rotten on you and me. My spidey senses tell me though that your at very low risk of any immediate problems and have nothing to worry about.

That seem pretty knowledgeable to me.
Told Mimi you said she was Wolverine from the X-men. She ask ”why is Gerry comparing me to a men’s antiperspirant brand?”

Think we’re lost in transition once again.
And the band plays on...

Peter

P.S. Chimi appreciates the 007 comment

Just finished watching Matt's video "Stove chat episode 2" and at 10:30 he brings up a question that a lot of people ask him about bell sizing, extracting as much heat as you can out of the flue gasses and efficiency. One thing I really keyed on was that "Heat extraction does not equal efficiency.".
If you havn't already seen this video it may be well worth checking it out. SCe02

BTW... Never even knew there was a man's antiperspirant called X-Men so I guess point of view works both ways!

Thanks for that Gerry,

I will check it out for sure.

Heres where we're at. Got the indoor part of the double pipe chimney flue set up and square today.
Rained most of the day so we got as much done inside as possible. Snowing now. Looks like it should be ok weather tomorrow, so will fill the void between the two pipes with perlite (mixed with a bit of clay) in the morning. Tested with just perlite and it was too light and had some static electricity thing happening.

Hope to get everything in place so that we can start testing inside tomorrow.

Want to test with just the exposed half barrels. Don't have the full length of 15cm pipe, recommended by Matt to run the full length of the floor. Have to drive 3 hours to Sapporo to get it. Probably next week.
In the meantime will test with the small piece of off cut pipe I have. Cut the end off the last half barrel I have and cut in two halves. Using that to span the gaps between my welded corner piece and the end of the dead-end bench. Planning to lay the half piece over the gap. It will overlap by a good 15cm on both sides.

My question here is if I overlap and use just cob to seal the seam can I test without using the metal chimney tape? Will end-up pulling the barrels apart several times after testing to adjust ect, after evaluating the system with each burn. The tape is $20 a role and I'm sure I'll go through a lot of it if I keep re-taping the half barrel seams with each adjustment. (see attached sketch)

Just want to get a working sealed version of the thing in the house thats safe to use. Won't do a full cob/rock/stuff cover till we are satisfied that the stove is drawing properly. Having said that, I am sure the dynamics  will change as we add mass. Just shoot from the hip and make adjustments as needed.

No tape on test, safe or danger?

Peter

Yes Peter;   Temp or permanent sealing with cob is 100% ok.
Your rmh will definitely work different as you add mass.
Try all ways of running it)  with short pipe in 1/2 barrels , with no pipe in barrels , and with Matts recommended longer pipe in barrels.
The one big  beauty of cob , is once you make it the first time. You can reuse it forever!  Do not be afraid to pop open a cobbed part , just re hydrate and reuse.

After you have your rmh up and running, you will want to keep a bucket of cob accessible for cracks or changes.  

Thanks Thomas.
Looking forward to testing and sharing the results as we go.

Cheers, Peter

P.S. just watched Matt video that Gerry recommended. Good bit of information for sure.

What brand of carbon monoxide detector are you using?

Graham Chiu wrote:What brand of carbon monoxide detector are you using?

Good question. Don’t have one yet.

Peter

Do you have safety goggles though...:)

One thing I’d like to address is the idea of “cob”. It seem to be a very general term thrown around to describe a building martial that includes sand and clay rich soil, as well as fiber at times. However, in my limited experience and with the info I have gathered I have come to believe that the ingredients in “cob” changes greatly depending on its application and the situation in which it will be used. Is this assessment correct?

If so can someone please share basic ratios/recipes for:

1. Cob for sealing air gaps
2. Cob for building cavity walls
3. Cob for covering barrels
4. Cob for building mass
5. Cob that incorporates insulation

Thanks, Peter

Hi Peter;
This is a good question.
There is no definitive answer. I will try to explain, but may confuse folks as much as enlighten them.

Cob is what you make it, with the ingredients locally on hand. It is not a make or break part of your build. It really is just sticky mud.
The local clay I used for my builds was very pure. I needed 3 times as much sand as I did clay. Pure clay will crack, adding the sand helps stabilize it.
Others have a local source of clay, with sand already mixed in and need do no mixing at all.
Adding cut straw to a clay mix makes it stronger and insulate's it with air pockets.
When possible use a fireclay to make a thin clay slip for assembling the core.

One thing I would like to point out.  Only on an exposed bench is the consistency of the cob important.
If your bench is encased.  By brick , stone , metal, even wood then your "cob" can be nothing but sticky clayee mud.
In fact after you have encased your pipes with a cob layer. You want as much stone or heavy solid metal in your mass, very little cob is used at all. The cob is nothing but a thin layer between mass. Filling in any air gaps.
When I went to build my first RMH I worried about the cob.
Now I can tell you that the cob is the smallest part of a rmh build.   Following the proper dimensions, a large transition area to the horizontal pipes, insulated away from the ground , supporting a floor sufficiently.
Those are the important parts of RMH construction .

Well Peter , I probably did not enlighten you at all but hopefully this helps.

Totally did!
Thank you so much...:)

Peter

Hey folks!

Here’s some photos of yesterday’s perlite/clay chimney insulation back-fill. We ran about 8.5m of pipe from the room to the top of the chimney (minus the “H” cap) with an ID of 2.5cm between the outside of our 15cm real chimney pipe and the inside of our 20cm cover pipe. We used just over 100 liters of perlite. Price: about $23.00 USD for 100 liter bag. Will update later on how effective the perlite insulation is. Took a bit of time to infill and about 8 bucket trips to the top of the roof. Filled full and then tapped from the inside of the house till it stopped settling. Then topped off. If it works the only downside I can’t think of is that we can’t open the double pipe later, without coming up with some way to keep the perlite from pouring out of the pipe and going all over the house. Made a quick cover ring for the ceiling out of an old stainless steel pot lid I found in the shed. Few miss cuts in the drywall ceiling and some unsightly marker as well, but all and all a good fit I think. More than likely going to remove the drywall ceiling next year and insulated directly in the roof. So not to concerned about appearance right now. Working out the manifold with firebox cutout and transition now.

Slab under fire box is 5cm sifted clay and about 50 liters of perlite. Clay seems pretty predominant. Not sure if that will be an issue. The bottom of the fire box is 5cm of CFB rated to 1400C. There is another 5cm of perlite heavy clay mix under fire box slab and an additional 12cm thick perlite and charcoal insulated earth bag layer buried under 15cm of tamped roadbase. We are now well above grade. It has been raining and snowing on and off for the past 3 days but now signs of dampness or moisture penetration at all. All seems and void around the room have been sealed with a mix of clay and perlite cob.

Here’s a few shots to show our process.
Feel free to comment or point out anything odd.

Cheers Hokkaido!

I just wanted to chime in and add absolutely nothing technical but that I love your artwork and sketches and will be hurling apples at you because of them  Good luck with your build, it looks great!

Love all of your ingenuity, especially the pot lid cover ring. Thank you for keeping us updated, its a joy to watch it all come together!

Cheers and beers!!!
We like Granny Smiths...

One Love:)

More progress from today. Getting close to liftoff...

Peter

Excellent progress! A wonderful transition from manifold to the bell bench...large and will allow easy low friction flow of exhaust gasses.
You both take to cob very well. I can't wait to see the finishing touches you are going to sculpt into this project. I can see it being a true masterpiece when finished.
PS. For your barrel, once polished if you add a drying oil or even cooking oil to it, the barrel will shine and make it look a lot more classy. The first few fires will make it smoke and stink a bit but will quickly fade. A similar process to conditioning a cast iron pan.

Sounds great Gerry.

Just working on sealing the transition from the manifold now. Height of the burn barrel and manifold are set with exactly a 4.5cm gap. That what is suggested in the builders guide for a 6”/15cm system. Everything is level and plumb.

Now need to set the heat riser and wrap. Plan to use chicken wire. Do we wrap the chicken wire directly on the CFB and then put clay/perlite mix on top? No sand in the mix correct? We are using the clay rich soil we have. Finely sifted with no rocks or gravel. This will hold up correct?

Think we can start test firing inside tomorrow. Any suggestion on length of burns for the first few burns? Length of time to rest the core between burns?

Please advise.

Thanks, Peter and crew

Nice!

Peter, would you mind putting your "plenum" picture into this thread?

https://permies.com/t/61657/Flue-exhaust-transition-plenum-pictures

Just that pic from the inside, and a link to your build discussion is perfect.

Thanks.

Peter Sedgwick wrote:Now need to set the heat riser and wrap. Plan to use chicken wire. Do we wrap the chicken wire directly on the CFB and then put clay/perlite mix on top? No sand in the mix correct? We are using the clay rich soil we have. Finely sifted with no rocks or gravel. This will hold up correct?
Think we can start test firing inside tomorrow. Any suggestion on length of burns for the first few burns? Length of time to rest the core between burns?

A CFB core is good to go as is. No perlite/clay needed. That's the beauty of it. 👍
Burning time is variable according to person. Fast and hot burns tend to promote thermal expansion quicker leading to cracks. Not a big deal as you can wet the cob and smear over them mostly.
Some cracks will occur no matter what you do though. No worries, its gonna happen but since your not at the finishing coat yet, all the cracks will be covered up again anyway.
I also remember Matt saying that he never waits, he just lets er rip.

Satamax Antone wrote:Nice!

Peter, would you mind putting your "plenum" picture into this thread?

https://permies.com/t/61657/Flue-exhaust-transition-plenum-pictures

Just that pic from the inside, and a link to your build discussion is perfect.

Thanks.

Hey Satamax,

Sure! Think it’s best to wait until we’re all sure it works, but more than happy to share.

Buried the metal “wing” of metal on the manifold, that I cut and folded out, in cob.

A bit concerned that the inside of the cob wall will crumble if that piece of metal moves due to heat. Let’s see.

Was debating weather it might be better to cut that piece off and stack fire bricks or CFB there instead.

Peter

Gerry Parent wrote:
A CFB core is good to go as is. No perlite/clay needed. That's the beauty of it. 👍
Burning time is variable according to person. Fast and hot burns tend to promote thermal expansion quicker leading to cracks. Not a big deal as you can wet the cob and smear over them mostly.
Some cracks will occur no matter what you do though. No worries, its gonna happen but since your not at the finishing coat yet, all the cracks will be covered up again anyway.
I also remember Matt saying that he never waits, he just lets er rip.

Roger that! Thanks Gerry

Think I’ll put a bit of perlite and clay around the base of the heat riser, where it meets the end of the burn tunnel. That should help to stabilize it, so that it doesn’t fall over. Anything else?

Peter

Peter Sedgwick wrote:

Satamax Antone wrote:Nice!

Peter, would you mind putting your "plenum" picture into this thread?

https://permies.com/t/61657/Flue-exhaust-transition-plenum-pictures

Just that pic from the inside, and a link to your build discussion is perfect.

Thanks.

Hey Satamax,

Sure! Think it’s best to wait until we’re all sure it works, but more than happy to share.

Buried the metal “wing” of metal on the manifold, that I cut and folded out, in cob.

A bit concerned that the inside of the cob wall will crumble if that piece of metal moves due to heat. Let’s see.

Was debating weather it might be better to cut that piece off and stack fire bricks or CFB there instead.

Peter

I wouldn't have, but that's easily fixable now no?

Oh exciting for you (and us) almost there!
I think you only have to consider your refectory cement when curing the fire, but considering you have already heated it up to high temperature and the individual pieces have room to expand, you might be ok now?
There will be air in the pieces and most likely be some moisture, when the moister starts to steam the pressure will have to escape.
When you build larger pieces of refectory, the normal procedure is to add burn out fibres. Tiny fibres that melt when heated and then offer escape routes for any moister or steam.
The top gap is a very much discussed subject and many people can get confused over the subject, I most certainly did!
The point is not to make it to small, just make it as big as practical.
I have done a fair bit of experimenting with riser hight and top gap, I have found my own fire works very well with a shorter riser than recommended and with a much larger top gap of 150mm but many people use much larger gaps of 300mm of more.
Of course everyones own design rocket fire, will have its own characteristics, the bottom area of my fire box gets to red hot after around two hours and the top plate get red hot after around 45 minutes. Barrel sides near the bottom get to around 200c quite quickly but I tend to limit the air supply and operate it at lower temperatures.
It all great fun.....

Peter Sedgwick wrote:Think I’ll put a bit of perlite and clay around the base of the heat riser, where it meets the end of the burn tunnel. That should help to stabilize it, so that it doesn’t fall over. Anything else?

A good idea. I don't know how pristine you want to keep the outside of your CFB looking or how it will hold up to occasional cleaning from a vacuum but you may want to look at covering it with something.... like aluminum foil? Not a biggie for sure but just something to consider before it gets all blackened up.
Also, can't remember if you have a cleanout for the second half of the barrel bench.

Satamax Antone wrote:

I wouldn't have, but that's easily fixable now no?

Easy to fix for sure. Gonna fire a few times and then probably check how the transition is holding up. Decide what to do from there.

Peter

Gerry Parent wrote:
Also, can't remember if you have a cleanout for the second half of the barrel bench.

Not putting any clean out anywhere. Matt says bell bench floor won’t need cleaning and the ash will serve as additional insulation in his experience. Will need to remove the burn barrel from the manifold, at the end of the season, to clean heat riser so that will give me access to everything in the front part of the system. Only place it could become an issue is if I run the 15cm exit flue pipe, horizontally inside the stratification chamber, to the end of the close out bench.

I’ll probably figure out a way to have a clean out in that scenario.

Does that make sense?

Peter

Thanks Mr. Fox!

That’s really useful info on the top gap.

Also, I’m extremely interested in this topic of castable refractory custom bricks etc. Want to experiment and try different recipes and combinations. Would love to start a new thread to discuss further, when this project has settled down.

Peter

Gerry Parent wrote:For your barrel, once polished if you add a drying oil or even cooking oil to it, the barrel will shine and make it look a lot more classy. The first few fires will make it smoke and stink a bit but will quickly fade. A similar process to conditioning a cast iron pan.

My dad said we should try mineral oil on the barrel. Says it won’t go rancid. Always love the olds man’s advice...:)

Makes sense to me Peter. Just making sure you don't have a dead spot that you can't get to if you ever need to.

Well I think your dad is right, but he may have other things in mind for the oil other than the barrel? :)

Gerry Parent wrote:Makes sense to me Peter. Just making sure you don't have a dead spot that you can't get to if you ever need to.

Well I think your dad is right, but he may have other things in mind for the oil other than the barrel? :)

Could be...:)

By the way, we have a rocket captain...

Here’s some techie numbers to look at. All I can say is the thing is ripping up a heat storm. I’m in a tank top, Chimi and Changa just ordered matching bikinis...

Will do a follow up with more images of the build later. Lots of drying and cracking along the seams as expected. No leaks and the chimney is warm to the touch on the second floor after the 45 bend. Burnt for about an hour. Let it rest for about an hour. Then fired a second time for at lest an hour and a half. No problem on start up, no smoke back and no issues with draft.

Lots more stuff to do for sure, but looks promising. Thanks to everyone with all your advice. Looking like it will be a well warm winter. Fingers crossed...

People beyond the wall:)