Advice on a RMH build in Hokkaido Japan

Thanks guys. I’ll try removing the extra barrel and run the system again tomorrow. The only other option would be to test insulate as is by adding IFB around the base of the Second barrel maybe. I don’t have access to Insulative batting at the moment.

Also, is this wood too wet?

It’s super easy to split and basically snaps apart when I hit it with an ax. Much easier to split than anything I’ve used in the past, but still bubbling.

Yoshida san is telling me this wood is “dry”. I’m in questioning. Hummmm….

Side note, I have a feeling most people that have a regular wood burning stove never really know if their wood in dry enough, except those using a moisture meter, because the bubbling happens inside the stove and they never see it.

Max I could try to remove the last section of ducting inside of the bell bench, but that seems like major surgery.

As far as I know Thomas the inside of the firebox CFB hasn’t deteriorated in anyway and the heat riser chimney is also fully intact.

Will try to do more cleaning inside tomorrow.

Thanks again for all your advice and patience.

🏔🙏🏽🏔

Venison and donuts for breakfast👾

Peter, when your stove was first pressed into service it had a very strong draft. Have you tested the draft on the stove lately? I.e. the draft should be strong enough to pull the flame off a lit match (or bit of newspaper) held over the feed-tube entrance, on a lukewarm to cold stove that hasn't been fired for a number of hours to the previous day. Seriously diminished draft indicates an obstruction somewhere.

Any chance you could take loose the vertical section of exhaust pipe spanning the distance between the floor and the ceiling box, to inspect that 90-degree elbow embedded in the cob just behind the barrel for obstruction, ash buildup, etc.? Stuffing a vacuum cleaner hose down through the 90 degree bend it should reach the second elbow inside the bench, or use a small mirror held down in the first elbow to visually inspect that 2nd elbow.

12 year old wood, kept in the dry of indoors or under roof, will be just fine. 15% moisture content (typical level for well seasoned firewood) will still tend to sizzle a little moisture out of the end.

Scots John wrote:My God those traps look barbaric!!!

I know what you mean.

I’m not a massive fan of killing stuff myself. But the locals do this to protect the crops and veggies. They just trap the deer kill them and bury them. So we decided to start eating them. Thought it was too much of a waste.

As for the traps themselves, they are using spring loaded wire traps the grab the deer by the foot. The plate part you see is not like the old bear traps with big jagged teeth like you are probably thinking. The plate just holds the wire open after it’s been spring loaded.

🦌🙏🏽🦌

Byron Campbell wrote:Peter, when your stove was first pressed into service it had a very strong draft. Have you tested the draft on the stove lately? I.e. the draft should be strong enough to pull the flame off a lit match (or bit of newspaper) held over the feed-tube entrance, on a lukewarm to cold stove that hasn't been fired for a number of hours to the previous day. Seriously diminished draft indicates an obstruction somewhere.

Any chance you could take loose the vertical section of exhaust pipe spanning the distance between the floor and the ceiling box, to inspect that 90-degree elbow embedded in the cob just behind the barrel for obstruction, ash buildup, etc.? Stuffing a vacuum cleaner hose down through the 90 degree bend it should reach the second elbow inside the bench, or use a small mirror held down in the first elbow to visually inspect that 2nd elbow.

12 year old wood, kept in the dry of indoors or under roof, will be just fine. 15% moisture content (typical level for well seasoned firewood) will still tend to sizzle a little moisture out of the end.

Hey Byron,

I was dreading someone might ask that about the pipe. Although I have been considering it. It would require me to cut out a section of pipe the somehow hold up the part running into the ceiling while I tinker with the section going into the cob bench. Probably easier than I imagine, but what I’m concerned about is the fact that our entire insulation section of the flu pipe from the ceiling up is insulated with backfilled perlite sandwiched in between the inside tube and second layer outside tube. (See earlier posts for clarification. Just dreading the thought of a mishap and a room full of unwanted perlite beads.

Again, still might have to be done.

I’ll have a go with your test. Outside temp plays a big role as well right?

Thanks again, Peter and Co

Peter, if you have aluminium tape? Cut a rectangle out of the bottom of that vertical pipe to check for clogging of the last elbow. And tape it afterwards.   You could rivet two pieces of flat metal to form tabs inside the tube, so the cut piece doesn't fall when you put it back in.

That could also help prime the stove.

As for firewood. Split a piece and touch the freshly exposed surface of the split with your lips. If it is cold against your lips after a few seconds, it is not dry enough.

Satamax Antone wrote:Peter, if you have aluminium tape? Cut a rectangle out of the bottom of that vertical pipe to check for clogging of the last elbow. And tape it afterwards.   You could rivet two pieces of flat metal to form tabs inside the tube, so the cut piece doesn't fall when you put it back in.

That could also help prime the stove.

As for firewood. Split a piece and touch the freshly exposed surface of the split with your lips. If it is cold against your lips after a few seconds, it is not dry enough.

Max! That’s amazing that you said this.

It’s very similar to what I was just laying in bed thinking. Don’t need to cut the pipe out, just a square hole. I have some extra pipe as well, so I can cut a larger square after and use that to cover. Then tape and ad an ant hill of cob to really seal it. Can probably cut a pretty decent sized square hole and not have a problem. Then just remove and recob when I need to check.

Like your idea, but no rivet gun.

This hole cover in the flu duct wall won’t create any sufficient drag for the air flow, or it’s just worth the drag because it will give me needed access?

In the future I will make a new stove with a much simpler exiting flu pipe system for sure.

Thanks for the tips.

Lips on wood. Roger!

Peter

Peter, i had explained in a previous post, but not well enough.

Satamax Antone wrote:

As well, cut an opening at the bottom above the elbow, that you'll close with another piece of pipe and jubilee clips, so you can prime and clean there.

HTH.

A rectangular hole. A piece of metal larger. And two jubilee clips. Plus felt underneath, or mud or superwool or whatever!

Ah, so that vertical un-insulated section of stove-pipe is not easily removable then. Mine has a slip joint there for easy removal, plus a "T" at that end of the bench, and a "ceiling box" to support the insulated section of class-a pipe passing through the attic space. At any rate, Satamax's suggestion of cutting an inspection port is excellent! Matter of fact, that would be the very first thing I'd do. Go for it.

Peter Sedgwick wrote:

Scots John wrote:My God those traps look barbaric!!!

I know what you mean.

I’m not a massive fan of killing stuff myself. But the locals do this to protect the crops and veggies. They just trap the deer kill them and bury them. So we decided to start eating them. Thought it was too much of a waste.

As for the traps themselves, they are using spring loaded wire traps the grab the deer by the foot. The plate part you see is not like the old bear traps with big jagged teeth like you are probably thinking. The plate just holds the wire open after it’s been spring loaded.

🦌🙏🏽🦌

Sorry I am not much use helping you with your stove but thanks for your comment above, where I live in Scotland, you could  go to prison for using such a trap but shooting deer with a guide is far more exceptable !
Some people travel from all over the World to shoot Red deer and they can pay a £1000.00 a day to hire a guide  and the privilege  to do so!
At least you are making an effort to eat the deer, looks like a big one too!
Your new barrel extension will make cooking difficult  otherwise you could sear  your venison on top of the barrel.

Satamax Antone wrote:Peter, i had explained in a previous post, but not well enough.

Satamax Antone wrote:

As well, cut an opening at the bottom above the elbow, that you'll close with another piece of pipe and jubilee clips, so you can prime and clean there.

HTH.

A rectangular hole. A piece of metal larger. And two jubilee clips. Plus felt underneath, or mud or superwool or whatever!

Hey Max!

Ok. Thought you were talking about the elbow in the flu running inside the bell on the floor, so I kinda disregarded your advice there. Sorry. My bad. Funny thing is if we were all in the same room we could likely fix all the problems in a matter of an hour.

Going to cut open the vertical flu behind the drum can and have a look. Probably duct tape a piece of garden hose to a vacuum cleaner and snake it down inside of the flu pipe. Will keep you posted on how we do.

Thanks again.

Next to no draft at the moment…

🙄

Have you tried alcohol priming ?

Half a liter of rubbing alcohol in the cold feed tube, light it, and blow as hard as you can to start the rocket effect.

Ok! This should basically explain a major part of , if not all of, the problem. I was told there was not much of a chance for build up this far down in the system so no need for clean outs. Think in our case because of the flu pipe running on the bottom of the half drum bell bench the suction pulled a lot of ash, soot, and most likely dusty baked clay, into this elbow spot.

Massive buildup. I tried the mirror trick but because I can’t get my head inside of the pipe there’s no angle that I can get a clear look down to the next elbow. I’m going to try some kind of cleaning brush and vacuum system rig to see how much cleaner I can get it. Then slap on a new piece of metal tape it shut and try the system again. Think we’re getting closer to something that might work again. Long live the dragon!

Peter and Co.

Good to see such an obvious cause, Peter. Can you put a half wall in front of the outlet as a trap to settle the fly ash and detritus before it gets into the elbow? Although I suppose that now you have an inspection/cleanout port you will simply make this a routine check at the start of the season....

I would check monthly.

Peter, find yourself something like this.



That you cut and plaster onto  your cutout. With an endcap for checking and cleaning.

Peter Sedgwick wrote:Ok! This should basically explain a major part of , if not all of, the problem. I was told there was not much of a chance for build up this far down in the system so no need for clean outs.

H'm someone is giving out advice without having decades of experience of heating with wood burning stoves. I've learn the exact opposite, in that All stoves, no matter what the design, need cleanouts. Even the massive roomy interior Russian brick stoves have cleanouts, and the huge Swiss contraflow masonry stoves too. And Ernie and Erica's RMH Builder's Guide calls for a "T" where the exhaust turns vertical to pass up out of the mass, and etc.  And having ceanouts guard against Murphy's Law catching up to you :o)

Great to see that you've zeroed in on the source of your Dragon's "constipation".  I was leaning heavily towards that last upward turning 90 degree elbow. It has two things working to clog it up. Outward bound exhaust ash, and downward falling chimney debris, primarily soot mixed with condensate, and the occasional bird's nesting material.

Your Dragon will roar again! And just in time for winter!  

Satamax Antone wrote:I would check monthly.

Peter, find yourself something like this.



That you cut and plaster onto  your cutout. With an endcap for checking and cleaning.

I’ll see if I can find something in Sapporo next time I’m there. Thanks Max

Byron Campbell wrote:

Peter Sedgwick wrote:Ok! This should basically explain a major part of , if not all of, the problem. I was told there was not much of a chance for build up this far down in the system so no need for clean outs.

H'm someone is giving out advice without having decades of experience of heating with wood burning stoves. I've learn the exact opposite, in that All stoves, no matter what the design, need cleanouts. Even the massive roomy interior Russian brick stoves have cleanouts, and the huge Swiss contraflow masonry stoves too. And Ernie and Erica's RMH Builder's Guide calls for a "T" where the exhaust turns vertical to pass up out of the mass, and etc.  And having ceanouts guard against Murphy's Law catching up to you :o)

Great to see that you've zeroed in on the source of your Dragon's "constipation".  I was leaning heavily towards that last upward turning 90 degree elbow. It has two things working to clog it up. Outward bound exhaust ash, and downward falling chimney debris, primarily soot mixed with condensate, and the occasional bird's nesting material.

Your Dragon will roar again! And just in time for winter!  

It was probably me taking Matt Walker’s advice out of context. When I first started to design and build we were just planning to have a straight pipe that went through the top of the bell bench and hang in space above the floor. Matt said with a bell style bench I wouldn’t need a clean out cause it would take a long time for ash to build up.

After that we ended up making some changes and adding the pipe on the floor of the bell bench that ran to nearly the end of the bench.

As you mentioned, this is where the main issue occurred. Lots of restricted vacuumed air pulling tiny particles down a tube, but there’s not enough power to pull them all the way up the vertical flue flue and out of the house, so they have nowhere else to go but fall back right at that elbow.

Lesson learned.

🙏🏽

After a full day of pampering with a facial and a pedicure, our young lady is back and she means business. Good God, I definitely need to hide the car keys now.

Here’s what we did for her. Photos below.

I ground down and cleaned up the rough cuts I made for the new VIP clean out (near the elbow) Should have done that before sticking my arm inside for sure. 🙄
Filed flush a bit of the crimping on the flue ducting as well. These two things I felt would give a cleaner seal when I slapped a new piece of metal on top to reseal and keep her leak free.

Bent the newly shaped cover over a large glass wine bottle to exaggerate the curve and have the metal along each side push back against the overlapping edges of the original flu pipe. Kinda making it spring loaded.

Also degreased all the metal, including the tire wire I used, with white vinegar and wash my hands well. Been having a bit of an issue with the high temp tape adhesion and I figured I’d see if that would help. (Know it’s important in gun bluing etc.)

Tied the new cover in place temporarily, once in the middle, then started taping from the top. Once the first top half was finished I tied off the top firmly, then moved to the bottom, removed initial tie, finish taping and retired, so that none of the tie wrap wire goes under the tape. Pro tip for anyone who’ll actually be as dumb as me and make a RMH with no clean outs😎

Mimi also found a way to hook two old vacuum wands together and she managed to vacuum out both the bell bench and the flue pipe inside to the second elbow. Because of the angle it’s impossible to get visual confirmation but based on the sound that the vacuum cleaner is making there doesn’t seem to be any more buildup in the second elbow from what we can tell.

I also ran some scrubby chimney cleaning Doohickey, we found in the Farm shed down at the end of the driveway, up and down the pipes a bit , nothing major.

Slapped the brick cap back on the end of the dead end bench and started her up…

Happy days…🏔😊🏔

Stats

Started with wood chips and small to medium size wood. (Mix of Japanese Maple and other local hard woods)

Temperature at start in vertical flue 22°C

Temperature after 20 minutes in vertical flu 105°C

Temperature after 35 minutes in vertical flu 122°C

After 15 minutes all signs of smoke from the chimney outside were gone.

Outside chimney exit temperatures, measured after one hour of burning 57.8°C

Local outside temperature 8°C

Weather mild rain and light winds

Burned now for just about 2 1/2 hours. No flames coming up out of the firebox and absolutely no smoke exiting the firebox at all.

I think we should add more mass.
A bit more chimney and maybe work on the feed tube if time permits.

This to me seems extremely good please feel free to comment and add any insight or if you have any questions please let me know.

We really want to thank everyone for their time patience and consideration.

In a tank top👙… Peter Mimi and ChimiChanga

🐕👨🏻‍🚀👩🏻‍✈️🐕

Peter Sedgwick wrote:


I think we should add more mass.

Well, one you could do, replace that vertical tube by small 60 litter barrels. It slows the gases down, without impairing the draft. And gives more time to the gases to exchange heat with the surroundings. Mass it could be.

Satamax Antone wrote:

Peter Sedgwick wrote:


I think we should add more mass.

Well, one you could do, replace that vertical tube by small 60 litter barrels. It slows the gases down, without impairing the draft. And gives more time to the gases to exchange heat with the surroundings. Mass it could be.

You mean replace the pipe, I just cut, with a small barrel? There isn’t very much space back their between the sliding doors and the front main barrel.

Yep, it's what i meant.

Two or three small barrels stacked on top of each other, or, a 35kg gas bottle.  



Like the one on the left.

Peter Sedgwick wrote: It was probably me taking Matt Walker’s advice out of context. When I first started to design and build we were just planning to have a straight pipe that went through the top of the bell bench and hang in space above the floor. Matt said with a bell style bench I wouldn’t need a clean out cause it would take a long time for ash to build up.

A long time for Matt is one or two heating seasons, cuz' after one or two seasons he does a complete tear-down and rebuild to modify the stove's design:D Just "ribbing" Matt Walker a bit. I've posted on his forum a goodly amount, some years back. He is quite the stove experimenter, and very knowledgeable.

Anyway, yes, with a really long half barrel bench, and Matt's done something close to 10 meters long or so if I recall correctly, with a vertically exiting "plunge-tube" exhaust at the far end, one can get by without cleanouts.

Obviously, with your low profile and "short coupled" ISA limited half-barrel bench, annual cleaning will be most beneficial to the Dragon's health.

For added mass, the first 2 meters of the vertical exhaust flu could be replaced by a "fat" brick / masonry chimney, to serve as a bell.

Edit: Matt's 30+ meter half-barrel bench build, Rocket Heated Seating for NYC Restaurant

Thanks guys!

I do like all these ideas and it gives me a better idea of possible options for heat extraction, however at the moment I’ve got so many things on my plate getting ready for winter in what is more or less an uninsulated house with a rotting foundation. This is really only temporary, two more seasons tops hopefully. After build something new and turn this into storage work space if still standing.

With that in mind I really want the most bang for my buck and basically use what I have around me and a bit of creativity with junk etc.

Max- Gas Bombay could work if I come across one that is free and will fit in that space. But I think we need mass no? Not more radiant in that tight space against the door.

Byron- all about seconds bells etc, but used bricks are not something I come across in a country they barely ever build traditionally with bricks. Tons of free stones. Really thinking of just adding mass to the base of the first barrel extension for right now.

Nice to see an old post like that from Matt. Sloping barrels I assume is to promote movement of air from one end to the other. I think I heard that somewhere before as well, maybe from Matt.

I do appreciate all these ideas, however it seems to me to make the most sense, and you are more than welcome to correct me if I’m wrong, but at the moment I should add mass to the new barrel extension, potentially an extension on the heat riser and, time permitting, maybe extending the height of the feed tube which would allow better control over air intake throughout the burn cycle. (Super long run on sentence)

Im not a super stove guru by any means, but try to give stats of what I feel would be useful information and numbers that everyone can relate to. Is their anything conclusions or insight you can draw from what I have included in my previous post?

My apologies but sometimes when we get into this ISA E = mc2 stoichiometric stove talk stuff I get lost. I’m trying to follow…🏔😋🏔

✌🏽

So happy to hear that your Dragon is up and rocking again!
Growing pains can be tough but glad to see that you persevered through it.Growing pains can be tough but glad to see that you persevered through it.

Yeah, Peter, for more radiant heat after the fire is out, mass is what you're after. "Rocking up" around the barrel's base extension will buy you some.

You'll still be loosing a good bit of heat up the vertical exhaust section by the barrel. To harvest more heat, that first couple of meters of exhaust flu could be enclosed in rock, held together with clay/sand mortar, wrapped with some screen wire to guard against it cracking and falling off with thermal expansion of the stove pipe, and then cob'ed over for good looks if desired.

You could start by first adding only a meter high section, with a portal formed around the new "inspection port" of course. Then check it's performance and add onto it, going higher, if the exhaust gas temps. are still running higher than desired. I seem to remember that 60°C or so is about as low as one should push it, when measured where the flu gasses are exiting the thermal mass, or in this case, the  "rocked" section of flu pipe.

Peter Sedgwick wrote:

Max- Gas Bombay could work if I come across one that is free and will fit in that space. But I think we need mass no? Not more radiant in that tight space against the door.

 

Gerry Parent wrote: So happy to hear that your Dragon is up and rocking again!
Growing pains can be tough but glad to see that you persevered through it.Growing pains can be tough but glad to see that you persevered through it.

Thanks Gerry!

I get myself in the same situation racing Against the clock to beat mother nature. Lesson learned and the take home here, for sure, is routine maintenance and seasonal cleaning for sure.

Now that the stove seems to be working fairly well I will do what I have time for and what makes sense, taking into consideration the resources we have in the situation and environment we live in.


Will keep posting and updating as we go.

Cheers Peter & Co.✌🏽🌞✌🏽

Satamax Antone wrote:

Peter Sedgwick wrote:

Max- Gas Bombay could work if I come across one that is free and will fit in that space. But I think we need mass no? Not more radiant in that tight space against the door.

 

Gotcha Max! Thanks

Byron Campbell wrote:Yeah, Peter, for more radiant heat after the fire is out, mass is what you're after. "Rocking up" around the barrel's base extension will buy you some.

You'll still be loosing a good bit of heat up the vertical exhaust section by the barrel. To harvest more heat, that first couple of meters of exhaust flu could be enclosed in rock, held together with clay/sand mortar, wrapped with some screen wire to guard against it cracking and falling off with thermal expansion of the stove pipe, and then cob'ed over for good looks if desired.

You could start by first adding only a meter high section, with a portal formed around the new "inspection port" of course. Then check it's performance and add onto it, going higher, if the exhaust gas temps. are still running higher than desired. I seem to remember that 60°C or so is about as low as one should push it, when measured where the flu gasses are exiting the thermal mass, or in this case, the  "rocked" section of flu pipe.

Thanks for that Byron.

These sound like options that are realistic for our present situation and not overly time-consuming. Will likely start with messing the extended barrel at the bottom and then potentially work some more rock mass around the vertical flue pipe, just depends on The outcome of the initial “massing” and what kind of configuration will work so that we still have relatively easy access to the newly created door for cleaning.

Will keep tinkering and updating as we go.

Peter

As you can see here, Chimi&Chunga are extremely excited about the resurrection of our young dragon!

🔥🔥🔥🔥
🔥🐕🐕🔥
🔥🔥🔥🔥

Just at the local picking up some stuff and saw these for sale.

Opinions at the local country “home center” down the road for wood burning stoves here in Hokkaido. When we tell people we are heating with wood this is the normal “tin can” everyone assumes you are heating with.

Average cost of one of these units is around $60-$80 USD.

Also an assortment of different types of flue pipes, ducks, vents, and valves.

Not a lot of options.

Lots of people use kerosene space heaters similar to the one shown here. We use this one intermittently when we want to slow cook food or dry laundry etc.

Do have one question. Like I said I have extra pieces of CFB laying around and I could add an extension to my riser, but to be honest the stove seems to be working relatively well is there any advantage to adding a riser extension?

I’m thinking, as I believe Glenn and others pointed out, that extending the riser would allow me to make the feed tube longer. That’s the only advantage I could possibly think of.

There is absolutely no draft issues at this point no matter what the weather is. Sunny 10° and no wind outside right now and stove is running like a charm. Stove hits around 100°C in just under 25 minutes with a medium size load of hardwood.

I’m assuming this temperature will drop slightly once I add some mass to the bottom barrel extension on the drum bell over the riser.

Peter

General rule of thumb: divide the height of the heat riser by 3, and make the feed tube that height (depth). Firewood sold here in the US, sold by the cord (4 x 4 x 8 feet) and face-cord ( 1/3 rd of a cord or 4 x 8 feet x 16 inch long sticks) is therefor commonly cut to a length of 16" (40 cm). So it is mostly a matter of convenience that a RMH's wood feed depth is made 16" (40 cm)  provided the heat riser is at least 48" (120 cm) tall.

Sized as such, the wood will be surrounded on all four vertical sides, and being in the "wind tunnel" effect of the wood feed, helps prevent the common cause (to short of wood feed or to long of firewood) of fire creeping up the sticks.

Byron Campbell wrote:General rule of thumb: divide the height of the heat riser by 3, and make the feed tube that height (depth). Firewood sold here in the US, sold by the cord (4 x 4 x 8 feet) and face-cord ( 1/3 rd of a cord or 4 x 8 feet x 16 inch long sticks) is therefor commonly cut to a length of 16" (40 cm). So it is mostly a matter of convenience that a RMH's wood feed depth is made 16" (40 cm)  provided the heat riser is at least 48" (120 cm) tall.

Sized as such, the wood will be surrounded on all four vertical sides, and being in the "wind tunnel" effect of the wood feed, helps prevent the common cause (to short of wood feed or to long of firewood) of fire creeping up the sticks.

Thanks for that Byron,

Super easy to understand.
My dimensions for our J-tube is based on the plans I got from Matt for his CFB J-Tube core , then modified according to stove pipe dimensions locally available here in Japan based in metric.

It’s 15cm x 15cm square though out the entire fire box and heat riser

Height of feed tube is 22cm from lip of The entrance to the bottom brick. (not measuring from center S is sometimes commonly practiced)

Length of the burn chamber is 54 cm long from the back wall of the feed tube to the back wall of the barn box just below the heat riser.

I will check the height of the heat riser later when I remove the drum to give you an accurate measurement but I made it as long as I could with one piece of CFP uncut. Ran all of these dimensions by Mat before building and he said they wouldn’t be a problem.

On another note, till now I have had a little experience with firewood and haven’t given it much thought but at the present time the wood that we are using is generally under 34 cm long.

I’ve read a number of places that the common rule of thumb for dimensions is  1/2/4 I believe

There’s probably a bit of room to experiment and find what works for our stove if any modification needs to be made at all.

Maybe best if I see what size pieces of CFP I have that would fit as an extension to the riser then give you more defined dimensions of what I’m expecting might work so you can give me some definitive advice as whether or not those numbers seem reasonable.

Thanks again for your patience and time.

Will keep learning.

Peter🙏🏽

Here’s my upgraded version for the bottom brick in our J tube. No matter what I did for mixing castable refractory the bottom brick always ends up spalling and just crumbling to pieces so I decided to take one of the insulated fire bricks I had and cut it to fit inside and create a new floor.

I just used some common handtools and a Diamond blade disk grinder. First I split the brick so that it was the proper height to match my original brick height. Then, working off of the custom wood mold that I had originally made, I just cut cut pieces, like a puzzle, and used a large piece of rusty sheet steel to sand and profile the bricks until they fit snugly together.

They are more or less a perfect fit with very small gaps but they are just on the floor plan and are used leftover fire ash to fill the gaps dry fit with continuous pieces of CFP underneath so in theory the bottom brick is more or less acting as a protection layer, to avoid damaging the ceramic fiber board.

I’ll keep you posted as I’ve only used it for about five or six days now but at the moment there seems to be no problem whatsoever.

Cheers🌈

P.S. my brick dimensions are custom to my stove design so not likely anyone can use this exact layout, however just for reference, splitting one insulated fire brick gave me enough material to create an entire floor plane for the bottom of my feed tube into the burn box.😊

Peter Sedgwick wrote:

My dimensions for our J-tube is based on the plans I got from Matt for his CFB J-Tube core , then modified according to stove pipe dimensions locally available here in Japan based in metric.

It’s 15cm x 15cm square though out the entire fire box and heat riser

Hi Peter, ah, you're within a couple of mm of being a 6" system size then.  

Peter Sedgwick wrote:

Height of feed tube is 22cm from lip of The entrance to the bottom brick. (not measuring from center S is sometimes commonly practiced)

Length of the burn chamber is 54 cm long from the back wall of the feed tube to the back wall of the barn box just below the heat riser.

The feed tube can easily be deeper (taller) to fit your common firewood length. Have a look at the 150mm RMH brick layout with dimensions on page 98 of the Wisner's The Rocket Mass Heater Builder's Guide, which calls for up to a 38 cm feed in that example. And on page 96, a 6" system with 16" feed, 23.5" burn tunnel, and 48" tall heat riser. With your stash of IFB, those can be stacked on edge to get the desired feed tube height. Careful to maintain 15cm x 15cm as the feed is built up. It's not to critical, could vary mm or two without compromising performance, but armed with IFB should be easy to keep it square and of the correct 15cm square.

Peter Sedgwick wrote: I will check the height of the heat riser later when I remove the drum to give you an accurate measurement but I made it as long as I could with one piece of CFP (CFP?, -->  CFB/Ceramic Fiber Board?) uncut. Ran all of these dimensions by Mat before building and he said they wouldn’t be a problem.

On another note, till now I have had a little experience with firewood and haven’t given it much thought but at the present time the wood that we are using is generally under 34 cm long.

Then I'd start by bringing the feed tube height up to around 34 cm or a little higher, depending on how the IFB stack up for convenience. Looking forward to your report on how well it works out.

Sounds great Byron!

I’ll take a look at the height of the present heat riser figure out what makes sense for an extension based on the scraps of CFB that I have then calculate accordingly.

Will keep you posted with the dimensions that I am proposing and see what you think.

Thanks again as always.

Peter

P.S. I’m super dyslexic so I use the dictation feature on my phone and sometimes I miss spelling mistakes etc. I apologize if it causes confusion😋

Here’s a quick look at my CFB riser extension project I did today.

Pretty straight forward. Just a few hand tools and a bit of squaring up with my trusty rusty sheet of metal. Decided to use some screws to hold this one together. Not even stainless, but I figure they won’t be a problem cause they are counter sunk “outside” the fire box and imbedded in CFB. Didn’t brake any rules.🔥 think stewing in with your fingers as far as you can is the way to go. Not using any pressure and letting the treads of the screws do the work. That way I’m not crushing the CFB as I drive them into place. Maybe I’m overthinking it but it seems logical and ended up relatively sturdy.

Made some more mounting brackets out of leftover pieces of galvanized steel siding. Cut to size and then added some groovy grooves to keep the stainless wire in place.

The extension adds an extra 15cm to our riser. Just an arbitrary number I decided to use after looking at the scrap pieces of CFB I had. Wanted to use as little CFB as possible and saved my larger scrapes for potential future projects. i.e. spanning insulated ceiling for a batch box etc.

Here are my new core dimensions:
(all numbers our end to end and not measured from the center)
Feed tube height: 22cm
Burn tunnel length: 54cm
Riser height: 127cm
Internal diameter of the car is 15 cm throughout

It’s hard for me to say this is an improvement. The stove is running well before. Now it’s running well as well. Not sure I gained anything, but it’s too early to tell and I don’t believe that I have made any adjustments that are detrimental affecting the stock performance at the moment.

Here are a few images to show you the process.

Peter & Co.