Advice on a RMH build in Hokkaido Japan

What's your chimney temp?  

175C° on the barrel top seems à bit low imho. Do you have a big top gap?  

Looking at the 100c°  on the firebox's  bottom is a bit high. May be insulating the rocket's burn tunnel and heat riser. Being careful with gaps as usual.

Satamax Antone wrote:What's your chimney temp?  

175C° on the barrel top seems à bit low imho. Do you have a big top gap?  

Looking at the 100c°  on the firebox's  bottom is a bit high. May be insulating the rocket's burn tunnel and heat riser. Being careful with gaps as usual.

Understood.
Have a 4.5cm gap as suggested in the builders guide for a 6” J-tube.

Will insulate more around fire box with off cuts of CFB before incasing in perlite cob.

Think my crappy digital thermometer is not very accurate. What max temp do I need on a digital thermometer if I decide to get a new one?

Will see how we go and keep you posted.
Should I be thinking of taking off the barrel and looking inside in the next few days?

Should I rewet the cracks and cob over or just fill the dry cob as is?

Thanks

Peter

Not sure on the chimney temp, but I can’t touch it.

Peter Sedgwick wrote:Not sure on the chimney temp, but I can’t touch it.

If your going to use your IR gun on the chimney (or other shiny/reflective) surface, you need to put a piece of tape on it, paint, or even magic marker on a small portion. The number will always be lower until you do this and very inaccurate. Best to use your candy thermometer to get the gas flow temps which are the true numbers your looking for rather than surface temps. It can be mounted at eye level on the pipe for convenience of reading.
Also, the amount of cracking your getting to me indicates that you need to add more sand. A high clay content when dry will always crack badly.
....and finally HOORAY !  on your first official burn. Love to see the girls in their bikinis.   :)

Looks great!
The outside of your fire box might well be hot, but any moister from the refactoring will be heating through the ceramic fibre and you may well find the temperature  gets a bit lower in that spot after a few fires.

For the fun of getting max temperatures you will need to feed lots of small dry sticks but you will find all that sort of stuff out for yourself.
Just take your time it will all come together in a few days.....

Thanks for all the advice.

So now we have a heat source. With that I feel relieved. Next order of business is evaluation of the engine to determine the best plan moving forward.

I will fire again today and lightly fill cracks as needed. Feel like I should take the barrel off, maybe tomorrow, and “look under the hood”. Even if it’s working well now I want to make sure that the interior is stable enough to weather the winter. Last thing we want is to be pulling the thing apart for maintenance in sub-zero weather in February.  

CFB is splitting in the corners where I pinned it together. Need to incase it soon. Low density CFB is super fragile.

Would like to start to discussing how to approach the “massing” of the bench for thermal storage, but will wait until I can provide more accurate and useful data to help with discussion and decision making.

Not sure we can call it a rocket mass heater yet, but we are warmer than we were yesterday.

Thanks again, Peter and the creatures of Hokkaido:)

Satamax Antone wrote:What's your chimney temp?  

175C° on the barrel top seems à bit low imho. Do you have a big top gap?  

Looking at the 100c°  on the firebox's  bottom is a bit high. May be insulating the rocket's burn tunnel and heat riser. Being careful with gaps as usual.

Can you please clarify exactly what “careful with gaps” means? There are “gaps” on the sides of the firebox feed tube top area, where the CFB meets the refactory brick.
Are these issues?

Peter

Peter, i meant the space between the riser and burn tunnel and the barrel and transition area.

If ever you add superwool, or some insulation.

Satamax Antone wrote:Peter, i meant the space between the riser and burn tunnel and the barrel and transition area.

If ever you add superwool, or some insulation.

Gotcha.

Thanks for making that clear.

Peter

Maybe we should see if they’re interested in using our new livingroom for the set on the next Flintstone’s movie...:)

So here’s what we’re looking at after roughly 10 hours of burn time. Just cleaned out the ashes from the burn tunnel. Below is a photo of what was left. At 5am and an outside temperature of -2C I can feel a draft pulling like a vacuum as stick my arm into the burn tunnel to scrape the ashes out. Fire starts within 30 seconds of lighting no issues. I am presently burning off cut building timber we got from an old farmhouse demolition site. Probably about 50 years old. Cut it up into thin kindling. Also using some larger logs, about 7-8cm in diameter. These burn much slower and at lower temperatures for sure. Mixing it up and experimenting.

Have stacked split fire bricks against the CFB on the outside of the burn tunnel. After 2.5 hours of continuous burning these bricks are too hot to touch for any length of time.

Don’t have the internal bi-metal thermometer installed in the 15cm flue yet, but I can no longer touch it after 20 minutes of burning.

Climbed to the top of the roof last night and checked the temperature of the gases exiting the “H” cap. Read 61C.

Few more temperature readings below. Although I’m pretty sure they are not very accurate. Will be getting a new inferred thermometer soon.

Placed rocks along the top of the half barrels to see how long it takes to transfer heat at different locations. The cob and lime plaster test brick (7cm thick) is only at room temperature after two hours of burning. Large rock (9cm thick) at the beginning of the half barrel bench is warm after 1 hour.

I will continue to experiment with these rocks and test bricks in the coming days.
Want to have a better understanding of the engine before building the fancy body.

Feel like we have a rocket style wood burning stove, but nothing that will make a mass heater yet. Will pull apart and see how the inside of the manifold looks later.

Here’s Chimi and Chunga in their new bikinis, handmade by Mimi at 5:30am.

Any advice on what I should be focused on next would be much appreciated.

Looks like a big snow storm at the end of the week.

Let’s see...

Cheers, Peter and crew

Hi peter; Great Job!
Isn't it nice, that great draft and ease of relighting !
Up next ? I would say get some cob on those half barrels! You need more mass.

thomas rubino wrote:Hi peter; Great Job!
Isn't it nice, that great draft and ease of relighting !
Up next ? I would say get some cob on those half barrels! You need more mass.

Would love too cover. However I want to be sure that we have enough temperature traveling the length of the half barrels to heat up the mass. Would rather spend a few extra days, like this, checking temperature and consulting, than hours on the back end hacking through piles of dried cob to fix the system inside the half barrels. These three, sitting at the end of bench, are only room temperature right now. We’ve been burning steady for 3 hours exactly. What should I be thinking?

Peter

Ha Ha Peter:  Dry cob pops off easily , don't fret about that. If need be, it is nothing to dissemble.
Your heat is leaving the barrels too soon.
You need mass to hold in the heat.

thomas rubino wrote:Ha Ha Peter:  Dry cob pops off easily , don't fret about that. If need be, it is nothing to dissemble.
Your heat is leaving the barrels too soon.
You need mass to hold in the heat.

I see.

Very enlightening. If you don’t ask you don’t know. So will start to pile rocks and cob on top now and see what happens.

Thanks Thomas!

Peter

Peter Sedgwick wrote:...I can feel a draft pulling like a vacuum as stick my arm into the burn tunnel to scrape the ashes out.

Some people have worked very hard to get their dragons to breathe like yours does - using fans, bypasses, priming ports etc, and right out of the gates! As it should be. Because of this though, if you want to keep that heat in the mass (once you get some) its best to close off the feed with something to stop your dragon from breathing all that hot air out the chimney once the fire goes out.

Have stacked split fire bricks against the CFB on the outside of the burn tunnel. After 2.5 hours of continuous burning these bricks are too hot to touch for any length of time.

A sign that the firebox could have even more insulation around it to keep it as hot as possible.

Placed rocks along the top of the half barrels to see how long it takes to transfer heat at different locations. The cob and lime plaster test brick (7cm thick) is only at room temperature after two hours of burning. Large rock (9cm thick) at the beginning of the half barrel bench is warm after 1 hour.

I think you are very smart to experiment like this. As you can see, the temps are much higher in the bench close to the stove and cooler as you go away from it. To help make it a bit more evenly heated (other than extending the exhaust pipe further down the bench as Matt suggested) the mass can be thicker closer to the stove and thinner towards the end. And/or, the thermal conductivity of the material that makes up the mass can be changed as well. There are charts online that show this so that you can select the correct materials that can match what your hoping to get out of your thermal battery. The conductivity efficiency is also dependent upon having no air gaps. This is where the sand/clay mortar comes into play connecting all your chosen mass together so it acts as one unit with no thermal breaks.

Here’s Chimi and Chunga in their new bikinis, handmade by Mimi at 5:30am.

Que wolf whistle....🎵 Awesome job Mimi!  Worthy of Hot Dog Magazine.

On page 111 of the builders guide and throughout this forum, ash scoops of all kinds have been made to clean out the burn tunnel. You'll find which one works best for you that also won't damage your CFB.
Your barrel that sits on the manifold barrel is sealed with aluminum tape. Works just fine but have you thought of using a band clamp to make it a bit more convenient? I know this is one place where mine sometimes smokes a bit when it is first lit up so it definitely needs to be sealed. (A flashlight is great for detecting smoke leaks BTW). Not sure it there's enough room to glue a fiberglass rope gasket to the manifold barrel then the band clamp to secure. Obviously a place where you don't want to cob over but still make it look nice.

Peanut covered eco hippiebar...:)

Looks great Peter;  Heat it up and let it dry some.  If your happy add more!

Thanks guys!
Will do. Appreciate the input. Cool tips. Been putting a bit of perlite mix near the base of the half barrels and on top of the first half barrel as it is way hotter than the other barrels.

Will insulate the feed tube and part of the fire box on the outside of the manifold. Should I think about doing the same thing to the other half of the burn tunnel on the inside of the manifold?

Also should I be insulating the outside of the manifold on the right side near the wall, as we don’t need heat going in that direction? Could dump a 100l bag of perlite and a bucket of volcanic pumice stone there with some clay. Thoughts on this idea?

Much thanks, Peter

P.S. any leads to where I can find those “charts” on line?

I had a IR gun that read to about 800 C, and I replaced it with one that read up to 1300 C as that's what Peter was reporting at the top of his batch box riser.  And I was getting errors at high temperatures.

Instead of using a staple, why not steel pins along the length of the join of the CFB?  Then it shouldn't split like that.

There's a design error in the bikinis. Dogs have about 8-10 nipples.

Graham Chiu wrote:I had a IR gun that read to about 800 C, and I replaced it with one that read up to 1300 C as that's what Peter was reporting at the top of his batch box riser.  And I was getting errors at high temperatures.

Instead of using a staple, why not steel pins along the length of the join of the CFB?  Then it shouldn't split like that.

There's a design error in the bikinis. Dogs have about 8-10 nipples.

Keep it clean mate:)

Yeah I have them pinned as well but the board slides off the pins. Banding the fire box the same way I did the heat riser would have probably been a better option I think. But I can’t be asked to take the firebox out to do that now. Think I’m just gonna incase the whole front side of the feed tube in more cut offs of CFB and clay/perlite mix.

Will have Mimi  redesign the swimwear. Maybe make a pinup calendar for the holidays...:)

Peter

Peter, congratulation on your new baby dragon.

Temps reading seem consistent with what i've seen in other builds. 371 on top of the barrel is nice.  61 at the cowl is about right. May be you can extract a smidge more.

As others said, get your mass on. More rocks, less cob! Try to avoid limestone. The denser the better!  Mind you heat release shouldn't be too fast.

An idea which came to my mind, in the first barrel, to check for the crumbling, you could cut a 20x20cm hole, and cover that with sheet metal, taped, then cover with just cob. Then you could open it in the future, to check. Or buy a  big T pipe, and cut it, so you have the small end  sticking up, put a cap over that, and cob all around. That would make a nice "cleanout"


Charts about heat capacity, thermal storage etc can be found at the engineering toolbox.

https://www.engineeringtoolbox.com/specific-heat-capacity-d_391.html

https://www.engineeringtoolbox.com/sensible-heat-storage-d_1217.html

There is a better chart somewhere, listing lots of different materials, but can't seem to find it quick.

https://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

If it was my heater, i would provide for  modifying the first part of the vertical chimney, into a small bell, in case i would need more thermal extraction. Just in case.


Does your room overheats?

Hth.

Peter Sedgwick wrote:Will insulate the feed tube and part of the fire box on the outside of the manifold. Should I think about doing the same thing to the other half of the burn tunnel on the inside of the manifold?

Remember what Satamax said earlier about possibly adding extra insulation and "being careful with gaps as usual." Answering for him, I would say that adding extra insulation is fine (and beneficial) just as long as it doesn't interfere with the flow of gasses by creating bottlenecks (excessive friction) that might affect performance.

Also should I be insulating the outside of the manifold on the right side near the wall, as we don’t need heat going in that direction? Could dump a 100l bag of perlite and a bucket of volcanic pumice stone there with some clay. Thoughts on this idea?

Its a place that probably won't receive any conduction transference to physical touch but still would provide convective heating to the room stored in the mass. If you would rather have the heat elsewhere though, then good idea. Customizations like these are what make RMH's so unique and personalized to your needs.

P.S. any leads to where I can find those “charts” on line?

You folks are absolutely stellar!!!

Thank you so much.

Kinda doing a bit of bohemian freestyle stuff right now and listening to to The Rolling Stones.

In the zone...Peter

Satamax Antone wrote:
Does your room overheats?

Does now that we’re trying to dry the bench out. Burn for 8 hours or so today.
But still very little heat at the end of the deadend bench. Going to Sapporo tomorrow if it is not heavy snow. Will get some more pipe and supplies.

Peter

What the sharp L in the bench indicates to me is that this quick direction change slows the gasses down even more where they don't have enough time to make it to the other end before getting sucked up by the strong exhaust draw you have. Extending the exhaust pipe opening to the other end of the bench (within lets say a foot)  and lowering its opening to the floor (possibly by putting that heat register fitting on it that I mentioned before) would help. Your draft may slow down as well with this modification so its length may need to be tweaked so you don't extract too much heat and hinder draft too much.

Hi Peter ;
My bench although larger than yours , took weeks to dry out.
Your getting there, you do have a working dragon now!  We just need her to warm up!

Peter and Company....  I encourage you to watch this guys videos. They are all fantastic and his style reminded me of you The Nito Project

Gerry Parent wrote:What the sharp L in the bench indicates to me is that this quick direction change slows the gasses down even more where they don't have enough time to make it to the other end before getting sucked up by the strong exhaust draw you have. Extending the exhaust pipe opening to the other end of the bench (within lets say a foot)  and lowering its opening to the floor (possibly by putting that heat register fitting on it that I mentioned before) would help. Your draft may slow down as well with this modification so its length may need to be tweaked so you don't extract too much heat and hinder draft too much.

Thanks for that.

Understood on all points.
Much easier to make educated decisions and do creative problem solving with something physical in front of you to work with. Probably going to tear the thing apart and rebuild before it gets too cold.

Peter

Bit the bullet and did a full rebuild of the half barrel bench in a snow storm today. Cobbing in sub zero weather is anything but a picnic. Clay was frozen as we were mixing. Added the flue pipe extension as Matt suggested. Total game changer. Actually ran it a bit below the floor of the half barrel bench. Dug it out and laid it to 145cm of the 200cm side of the dead end bench. 1/4 of the pipe sits below floor level and the end tappers back to grade with clay. I’ll do a drawing later. Working well I think and the gases move much more evenly. Here are some images. Also added a stainless P-plate. (Photo below) outside chimney insulation is not as hot as before, but draft seems good. Pretty amazed seeing most of the materials we used were coved in snow and partially frozen. Will update more later. 50cm of snow on the horizon. Glad we have a stove. Now all we need is mass. In its present state heats up quick and cools down quick.

Long day, we’re cooked, but warm...

Peter and crew

Well done Peter!

I think many will enjoy your build pics in the future.

I've had 30cm of snow last night.  At least the ski season will start on a good layer of natural snow.

Your both real troopers in your quest for heat! Thank you for the updates. That was a good idea to lower the exhaust pipe extension to give more room for the heat to stratify.

Thanks folks.

Here’s a quick sketch of how we laid out the internal flue duct in our bench. Having it partially below ground level was actually a mistake because the original 90 elbow joint from the vertical 15cm flue pipe was laid in first and then I added more clay perlite on the floor of the half barrel drum so I had to dig out some of the floor to keep the pipe running flat on the ground. Also, the fact that the second half of the flue, after the “L” corner, is in the middle of the chamber floor is a miss cut on my part. Both mistakes seem to be working out pretty good and are giving an even distribution of hot gases.

A few thing I have noticed about the new setup.
1. End of bench is much warmer
2. Lower sides of half barrels are much warmer
3. Second floor perlite insulated 20cm flue pipe temperature is not as hot on the outside. Can touch with no problem even after 2-3 hours continuous burning
4. Draw of the rocket has not changed all that much.

Also started to add mass. Used only unsifted claysoil and roadbase is a thick mix. Smeared that on the tops of the barrel about 1cm thick. Then stuck rocks in it while it’s wet. Debating what to do with the sides. Especially the area between the edge of the room and the barrel. Space seems quite large and I’m afraid that if I just infill with rocks and mass, the heat will be too “deep” in my mass and I’ll never feel it.

We lined all the exterior edges of the base area around the half barrel bench with several coats of perlite/clay thinking of adding even more insulation to help retain the heat and direct it where we want itmost, the surface of the bench.

Manifold and firebox are also heavily coated with a few centimeters of clay perlite. No more heat lose there.

Not very much smoke from the chimney and the stove seem stable. Burned for at least 8 hours today straight. Snowing out side with strong winds and -3 to -5 temperature. No trouble. Just don’t want to over mass the thing and lose drafting and reliability.

Any thoughts on how to approach would be very helpful.

Cheers Peter and crew

Just fill that flat.

My mass goes from 25 to 45  after 3 or four burns. That's  enough. I can leave it  for two days without buring in the autumn. And It will flywheel from 45 down to 25, radiating nicely.  I have aproximately 4 tons of mass.

Nice that its all working out, even if some of it was done by mistake! Best advice I can give is to make sure you have plenty of dense materials for your mass and just fill the voids with clay/sand.
As you probably know, the more dense, the longer the heat retention. Its all a balance game of how much and where to put it so it meets your needs. Sorry can't be more specific than that.

I can imagine how your house must be very atmospheric and I am sure you will remember this time of your lives for a long time.
What with the snow and your isolation, with the time scale and learning curve and now... just in time ... the heat!  

So does the fire actually warm your house?

Peter Sedgwick wrote:No trouble. Just don’t want to over mass the thing and lose drafting and reliability.

Any thoughts on how to approach would be very helpful.

Cheers Peter and crew

My understanding is that you don't want to take heat away from the combustion chamber as that needs to be as hot as possible to burn all the combustibles but after that adding mass should not affect the draft.
If you're seeing some smoke past the initial burn that suggests that your fire isn't as hot as it could be ... unless you're actually still seeing moisture being driven out

For the most part, I would agree Graham. The ISA would probably have a lot more influence on draft than mass ever would but..... after you tear down your heating system during a cold snap and have to make frozen cob out in the cold, you would tend to want to play it safe and proceed cautiously too.  :)

Fox James wrote:I can imagine how your house must be very atmospheric and I am sure you will remember this time of your lives for a long time.
What with the snow and your isolation, with the time scale and learning curve and now... just in time ... the heat!  

So does the fire actually warm your house?

It has been a learning curve. And everything is so sign specific. Feel like we have a pretty good understanding of our basic materials that we are working with right now. Understand the consistencies of our clay slip mix, how to process it quickly, how to apply it, and the general drying time. We are adapting and making our own recipes by feel. This type of experimentation and adaptation is something Mimi and I do all the time with our previous jobs and hobbies so comes as second nature. This part I am confident with.

Now I am beginning to understand the burn patterns of the 15” j tube we have.
I can light it with out a problem, so not concerned with that part right now either.

What does concern me is the uninsulated state of the old house. Was able to heat 3 rooms last night, feeding the fire every 10-20 minutes all day.

What we have right now is not a rocket mass heater. It’s a few metal cans, some ceramic fiber board, and mud and rock that are beginning to dry and take shape.

I am laying in a warm Japanese futon bed typing this message, but don’t want to get up right now to go pee cause the house is freezing. “Rocket Mass Heater” bench is stone cold.

Right now we can tolerate as we adjust and work out the kinks. It’s February that got me nervous. That’s when the winter party really kicks in.

Could the bench be too big, too long?

This project is an idea I cooked up from a few videos an articles I read on the web. Sold the idea to the lady. Now have to produce the goods to keep the crew happy and cozy for the winter. Still a bit of Bear Grills survival on the day to day.

20cm new snow outside, just started the dragon. She’s hungry...

Peter

Hi Peter;   Mass is everything.   It is your heat.  
The more mass you put over your barrels , the longer they will hold heat.