Batch RMH build in Sweden

Haven't had the time to fix the air intake yet. But i found where it says how big it is supposed to be. 20% of CSA is 3 times larger than what i made. Haha. It will be done soon though. Mass is filled with clay/sand/brick scrap. Burning wood now to maybe accelerate clay dry time and it is also a bit cold outside.
Drag is instant and a quiet hum os heard from the fire. Nice.

Added some bricks to the top of the bell to soak the heat and not ignite roof because it is close to the wooden roof. Will make that nicer soon. Has anyone a nice idea how to protect the roof from heat except the bricks? Vermiculite in roof?

Also, when using the ceramic board, how is the best way to fasten it to itself? I used glue/sealant for 1000degrees but it wont stay in place after fire. Any tips?

Thomas, you're not cooking atop of that  steel "bell" ?

Make a brick oven on top of that!

It is 2m up so no oven, it is a bit too high up. 😁

Thomas Holm wrote:It is 2m up so no oven, it is a bit too high up. 😁

A little pizza warmer. And you keep a stool by the batch rocket.

Haha. Why not?

Your barrel is quite big, i would get 8 50x50 cm slabs Don't know about Sweeden, i get mine on the other side of the border. In Italy. Four on top of the barrel, cut to size. Four courses of bricks on the perimeter. On 280° or so. The four other uncut slabs on top of that, with weight on the edges, to keep these flat. And a metal roundish door.

Not much work nor sweat. And you can cook stuff in there. With a stool.

What kind of slab/stone do you use Satamax? Havent really thought about it that way but it will probably work just great. 😁

Thomas Holm wrote:What kind of slab/stone do you use Satamax? Havent really thought about it that way but it will probably work just great. 😁

Thomas, i use these.




I get those at "Blanchet" a supplier on the other side of the border. This is tough stuff for pizza ovens.

50x50cm, X 5 or 6 thick.  

Photo from this build.  https://permies.com/t/44806/Cobbling-workshop-heater


I know you can get this size in France too. Or similar, from cœur de foyer  https://www.coeurdefoyer.fr/29-dalles-refractaires

Prosiref too, le Panyol also, i think.

May be SVK


On cœur de foyer's site, i saw this, which could be an option, well, may be not, you'll need to insulate.

https://www.coeurdefoyer.fr/fours-en-fonte/78-four-a-bois-en-fonte-famille.html

Or a little kit from Panyol.

https://www.lepanyol.com/en/wood-fired-oven-bread-pizza-le-panyol-66.html

You don't have  those cheap pizza ovens kits, in sweden?

Like this



I think this would be the best solution.

We don't do cheap in Sweden... Everything is expensive. 😁

I love those pizza ovens, it is a future plan for the porch/outdoor kitchen dream.

Is it actual stone or like big bricks? Haven't seen those here but i will look more. Thanks!
Edit. Used Google translate so I know know it is bricks. Thanks!

Yep, brick slabs.

Ok, made a bigger primary air inlet. 105x60mm is 6300sqmm. 200mm is the diameter of the heat riser. 20% of the csa is pretty much 6300sqmm and as i understand it what is required. It still pulsates when burning and smoke from the chimney is pretty much pitch black and smells nasty. Again, opening the door to let in more air makes it stop pulsating and smoke turns white in the chimney.

Alot of work was put in to make the primary air larger so feeling a bit bad right now. Please help, am i missing something?

A few thoughts. My bell is 700mm. Heat riser is 350mm outside. It makes bell 4 times CSA. Where the bell sits on the bricks it narrows down to barely half that and the pipe to the bench is located in the bottom of the brick part. ISA of bell is approx 2.7sqm. If the brick part counts as part of bell its approx 0.6sqm.The pipe is 200mm. Bench is half a 600mm pipe that is 5.5m long. ISA is approx 5.2sqm. My ISA is a bit low , 2.7+5.2+0.6 is 8.5sqm and is what I was aiming for as I read somewhere that a slightly lower ISA is better than a too large ISA that might cause bad draught.

Reading another thread here, restriction down the line is bad. I have a few points where it might be a case of restriction? The lower part of my bell is not 4x ISA. Barely half that due to how i constructed it, with the bell sitting centered on the heat riser and partially on top of the firebox. It makes sort of a shelf inside the bell. Maybe this is a problem?

The part where the flow enters the chimney is a pretty sharp 90 degree turn. The 200mm pipe is put straight in and meets the square vertical chimney.

Well, except where the barrel sits on the bricks. I don't see much  off the recommended dimensions.

At the barrel ( metal bell) bottom  the transition to the bench, i say usually you need at the very least 1.5 times the CSA.  3 times for a batch is better.  You say two and a bit.

This is what you're talking about?





It seems all right to me. Or is the problem above?

As I see it, your steel bell is 4 times system size. Which is already not much, I use to recommend 5 times. The lower part of the bell, done in bricks is 2 times system size, being far too cramped.
You don't say anything about the transition from bell to bench, this should be open the full width of the half 600 mm pipe in order to ensure there isn't a pinched spot.
And from the end of the bench a horizontal pipe of 200? mm is leading back to the chimney. It might be that this piece of duct is causing the pulsing.

A couple of questions: this pulsing, does it occur only when the firebox is hot?
I did notice a bypass between bench and chimney, is this open when pulsing is going on?
Which of the two secondary air provisions do you use, p-channel or floor channel? And in case it's the latter, which horizontal and vertical size is it?
What's the size of the top gap, between riser and bell top?

What you could do is to keep the door open a crack at all times and/or burn bigger logs. The door open means air velocity is higher through the system while the front of the fuel is cooled much more so fewer burnable gases are generated at any given time.

Thanks you Peter for the response!

The transition from bell to bench is the 200mm pipe. It is not full width at all. I thought the CSA was good enough but maybe from bell to bench it is different from bell to bell as I have seen those with only a pipe to connect them.
There is no bypass, what is seen is an extension of pipe for access to chimney when cleaning.
Inside bench is the output to the chimney att approx 8cm from floor in bench. Made a conical shape at 400mm diameter. It can be lowered but not put higher at this point.
The pulsating comes when the wood starts catching fire for real. I can see black smoke just before that coming from the front of the fire to the back of the firebox, causing a circulation but not coming out in the room. The black smoke in the chimney, is that from too little oxygen to the fire?

The are a few pictures and doodles at the first page of this thread, maybe that can make it easier to see how it's done.

Also, it has always (a few, maybe 5 burns in total, only small burns) produced a light white smoke that dissapears a meter from the chimney, not at a forced flow but very dreamy if that explains it's behavior.

Thank you so much for commenting, I need the support and somewhat fear the large undertaking i feel might be needed to make it work.

Peter van den Berg wrote:As I see it, your steel bell is 4 times system size

I understood  4 times CSA remaining around the riser, and X2+ CSA at the bottom.

Thomas Holm wrote:The are a few pictures and doodles at the first page of this thread, maybe that can make it easier to see how it's done.

Also, it has always (a few, maybe 5 burns in total, only small burns) produced a light white smoke that dissapears a meter from the chimney, not at a forced flow but very dreamy if that explains it's behavior.

Thank you so much for commenting, I need the support and somewhat fear the large undertaking i feel might be needed to make it work.

This is steam. That's normal.

Forgot to answer about the P-channel. Its 72x24mm inside. It goes under the insulated firebox and comes up in the middle of the heat riser, approx 10cm protruding from floor.

Firebox is W275 x H415 x D570 mm

Opening to heat riser is 65x320mm and 50mm deep. This is poorly done as the ceramic board was glued to its mating part and glue came loose in first fire and the board parts are a loose now. Not sure how to best fix that if glue (1000 degrees approved) doesn't stick.

Some more pictures to help.

The biggest blooper I am aware of now is the p-channel. Actually it is neither a floor channel or p-channel since it ends in the middle of the riser. So there's some explanation to do.

The vertical stub of the floor channel should be about 5% of riser csa, square and reaching to about half the port's height. Size for a 200 mm system should be about 40x40mm internally.
Situated just in front of the port, not behind. The horizontal part, the feed, should be twice as large as the stub, so for this one could use two ducts side by side, the same size as the stub.

Every object inside or behind the port will cause the thing to produce black smoke. What exactly this is caused by remains unclear, presumably something to do with disturbing the double vortex at that spot.

The above is the most likely cause of not performing to specs. I am quite puzzled why you did it like this, the batchrocket site is quite clear about this particular point. This batchrocket design is what we call "a tight design", change something it doesn't matter what, and it won't do what it says on the tin.
My advise: rip out that channel, build and install a proper one exactly to specs and it will work. Whether or not as a result the pulse behaviour will be gone can only be tried.

And oh yes, the port at 65 mm is a bit too narrow, this should be 72 mm or very close.

Oh. It's a blooper for sure. Will correct it and try again. Have no explanation for this, it's just a thing that happened. Thanks for bringing this to my attention. It's quite obvious now that you point that out.

Peter van den Berg wrote:The biggest blooper I am aware of now is the p-channel. Actually it is neither a floor channel or p-channel since it ends in the middle of the riser. So there's some explanation to do.

The vertical stub of the floor channel should be about 5% of riser csa, square and reaching to about half the port's height. Size for a 200 mm system should be about 40x40mm internally.
Situated just in front of the port, not behind. The horizontal part, the feed, should be twice as large as the stub, so for this one could use two ducts side by side, the same size as the stub.

Every object inside or behind the port will cause the thing to produce black smoke. What exactly this is caused by remains unclear, presumably something to do with disturbing the double vortex at that spot.

The above is the most likely cause of not performing to specs. I am quite puzzled why you did it like this, the batchrocket site is quite clear about this particular point. This batchrocket design is what we call "a tight design", change something it doesn't matter what, and it won't do what it says on the tin.
My advise: rip out that channel, build and install a proper one exactly to specs and it will work. Whether or not as a result the pulse behaviour will be gone can only be tried.

And oh yes, the port at 65 mm is a bit too narrow, this should be 72 mm or very close.

So I fixed the floor channel (not P-channel) this morning and will try it tonight. Have read batchrocket.eu what feels like a hundred times and yet missed that very elementary detail, what a blooper, haha. Well well, errors are being made all the time, and checking your own work is something I am terrible at, so looking forward to firing it up again. Don't know what to expect but if this thing doesn't make it soon I will have to make a decision if I can continue or think about an easy solution. It was fun to begin with but painfully slow progress due to life, work, single parenting etc and living in a restoration project really is beginning to take it's toll. No more whining, sorry for that, but that's where it is right now. Hopefully I can make some changes and get it going soon! Thanks all for contributing, I really need it.

Ok. First burn after remodeling the floor channel. Channel is 72x22 and the vertical is 40x40 and sculpted as pictured at batchrocket. Pulsating is still there, it comes basically at the same time as the second burn starts going. Opening the door works to stop the pulsating. However, now the smoke is black and smells really bad no matter what I do. Opening door or not does not matter. Only black smoke. Weird.

I use mixed dry wood, birch and pine/fur, relatively small pieces but not tinder size. Fireplace half loaded.

I assume my faulty lower bell/transition to bench is too tight and possibly responsible for this phenomenon. I'm out of ideas how to fix it without tearing everything down and starting over.

Is it crucial for the bell to be centered over the heat riser?

Thomas, even with the bypass open? All the joints, welded or covered?

There is one thing. I find the port extremely wide compared to the firebox's width!



Another thing. May be your plunger tube is too low in the half barrel.

Your barrel to bench transition, doesn't seem that bad to me!

There is no bypass. Joints are a mix of welded and covered.

The secondary air port? It is to spec.

Plunger is possibly to low yes. 8cm from bottom but calculated minimum was 5cm. Can make it slightly higher if i dismantle it and remodel it.

Satamax Antone wrote:Thomas, even with the bypass open? All the joints, welded or covered?

There is one thing. I find the port extremely wide compared to the firebox's width!

The black smoke and the smell is confusing me. I guess it is poor combustion from poor flow?

Another thing. May be your plunger tube is too low in the half barrel.

Your barrel to bench transition, doesn't seem that bad to me!

The rear of the firebox's port. Entering the heat riser.

That looks extremely wide!

Ahh, that's because the photo was taken before i put the ceramic board pieces back! Sorry, I should have explained that.

Well. Daft question. Are those pieces of ceramic board well stuck to the firebox's edge? What depth are these?



If anything over 5cm deep.  That's no good.

Re checking your plunger tube. It seems awfully low. You say 8 cm?

re checking your pics. The funnel at the end of the plunger tube is very  flat flared. It seems more than 5cm width for 5 cm height. (45°)  So this might well be a problem.

If you've chosen 8 cm gap. That means that with a X3 the CSA  That would mean 37.5 cm outer circumference of the funnel. Am i far?



Let's assume the height of the cone is 5cm.

8+5 13.

20cm X PI 62.83

62.83 x 13 =816.814 cm².

If the funnel edge is 37.5cm diameter, So 117.80 cm circumference. X the gap of 8cm.  942.47cm² Which is the X3 CSA  i have used to guesstimate.

Your 20cm  pipe's circumference, multiplied by the gap (estimated) of 13cm makes 816.814cm², so less than recommended ( by Peter) X3 CSA minimum

(well, remember that this is from the top of my rotten head)

Yes i know, i said earlier you could may be get by with 1.5 times CSA. I guess i'm wrong.

But you see my point above. Funnel too shallow. ney working. Imho.  Raise that bleeming edge to 10cm!


then i'll come to the other point. Or points.

Well.

About the chimney?

What is your width and depth at the red line?





Then, have you filled above the half barrel bell?  If not, may be putting coton covers on it, to raise the temp could help. Your temps outside are not cold enough yet to drive a big stack effect. I guess you haven't warmed up the chimney before.

If the transition from 20cm tube, to the chimney is bad, i think i can offer a solution.

The pieces are 5cm.

Satamax Antone wrote:Well. Daft question. Are those pieces of ceramic board well stuck to the firebox's edge? What depth are these?



If anything over 5cm deep.  That's no good.

Re checking your plunger tube. It seems awfully low. You say 8 cm?

It's 30 degrees if I remember correctly. 400mm diameter. The 8cm gap was the maximum I could get with the current solution. You said at least 10cm at the time so I should have listened to you back then.
Did want to minimize the height of it all due to the surrounding environment, but will try to raise a bit. Its not that much work.

Thanks Satamax! You are a very helpful and I am very thankful.

Satamax Antone wrote:re checking your pics. The funnel at the end of the plunger tube is very  flat flared. It seems more than 5cm width for 5 cm height. (45°)  So this might well be a problem.

If you've chosen 8 cm gap. That means that with a X3 the CSA  That would mean 37.5 cm outer circumference of the funnel. Am i far?



Let's assume the height of the cone is 5cm.

8+5 13.

20cm X PI 62.83

62.83 x 13 =816.814 cm².

If the funnel edge is 37.5cm diameter, So 117.80 cm circumference. X the gap of 8cm.  942.47cm² Which is the X3 CSA  i have used to guesstimate.

Your 20cm  pipe's circumference, multiplied by the gap (estimated) of 13cm makes 816.814cm², so less than recommended ( by Peter) X3 CSA minimum

(well, remember that this is from the top of my rotten head)

Yes i know, i said earlier you could may be get by with 1.5 times CSA. I guess i'm wrong.

But you see my point above. Funnel too shallow. ney working. Imho.  Raise that bleeming edge to 10cm!


then i'll come to the other point. Or points.

Can't find the numbers now but when i checked it it was basically equivalent to the 200mm pipe. Otherwise I would not have done it like this. Will check that again. The transition to chimney is a sharp 90 degree turn, please feel free to suggest better solution.

The half barrel is covered in clay and still a bit wet.

Satamax Antone wrote:Well.

About the chimney?

What is your width and depth at the red line?





Then, have you filled above the half barrel bell?  If not, may be putting coton covers on it, to raise the temp could help. Your temps outside are not cold enough yet to drive a big stack effect. I guess you haven't warmed up the chimney before.

If the transition from 20cm tube, to the chimney is bad, i think i can offer a solution.

Well, since you need to raise that pipe with the funnel.

What i would do, is make a  cutout of the width of the of the inside of the chimney; in the face they are jointing with the tube. About 60,70 cm high. Or whatever is needed. And rebuild a little wall against your chimney, to have a better transition area there.

If you see what i mean. That would shorten your pipe entering the chimney of  the width of a brick.

And also, do you have a photo taken from the top of the riser looking down  into your first transition area? It doesn't seem too bad to me. But what do i know.

Also, if you do that little wall. Make a little door above or bellow your tube, to have a cleanout there. You won't be sorry.

And, there is a trick you could use, temporarily, to heat up your chimney. Make a bypasss from your big horizontal cleanout, to your horizontal tube cleanout.

No pic in transition area besides the one with rebar on top earlier posted. It's not the best transition though. Its among the first brick work I did and found it harder than I thought it would be. Probably not the worst either. Improvement is possible! Though i find it hard to picture how i would do it practically. I was googling pictures when doing it but didn't find anything that i thought was inspiring and useful. Maybe a case of bad google-fu.

I understand the wall and transition idea. Not to hard to do, thanks for that! Since I have to raise the funnel thingy it is easily done at the same time.

Satamax Antone wrote:Well, since you need to raise that pipe with the funnel.

What i would do, is make a  cutout of the width of the of the inside of the chimney; in the face they are jointing with the tube. About 60,70 cm high. Or whatever is needed. And rebuild a little wall against your chimney, to have a better transition area there.

If you see what i mean. That would shorten your pipe entering the chimney of  the width of a brick.

And also, do you have a photo taken from the top of the riser looking down  into your first transition area? It doesn't seem too bad to me. But what do i know.

I have thought of a bypass. I could do a simple sviweling valve in the mass just after the big cleanout. Shut off a little more than half the mass. Don't know if that helps enough?

Cleanout is good. The little round door is a cleanout for chimney but its a long way, hehe. This is because I want to have a brick/concrete built kitchen top with stove on top and all pipes will be hidden under it.

Satamax Antone wrote:Also, if you do that little wall. Make a little door above or bellow your tube, to have a cleanout there. You won't be sorry.

And, there is a trick you could use, temporarily, to heat up your chimney. Make a bypasss from your big horizontal cleanout, to your horizontal tube cleanout.

You pictured the same as this?

Those two cleanouts. I would try to change the top plate of the big one, temporarily, and fit an elbow to the little cleanout. See if that works better.  

If it doesn't the problem lies in the transition area or the chimney.

If it works better, it's the bell the problem.  

You can even bodge stuff, with an elbow which is smaller, and filling the gaps with rockwool.

Yes! Very good idea!

Satamax Antone wrote:You pictured the same as this?