175mm Build

Another evolution on my plans! I finally got around to removing the cupboard that was in the space we plan to use. Turns out that it had a 50cm cavity below it!
This led to some thinking and we came up with this design.
The fire box and riser is still in the same place but slightly smaller. Scaled to 175mm (7")

My old hot water service will provide the barrel to go on top which will be around 1.4sqm of bell ISA.
This will sit directly on top of a brick bell built into the floor that is 2.3m wide x 40cm deep x 1m high which ends up providing the remaining ISA leaving us at 7sqm which is close to to the 7.2 specs.
The flue will be stainless and exit through a hole in the bench next to the hot water service part of the bell.

This is much more streamlined than the original design that I had planned.
I also intend to build the core inside a steel box that can slide through the wall penetration and be removable for servicing.

I've made a couple of assumptions:
That due to the barrel and brick bell being combined rather than separate that I do not need to remove 15% of ISA total.
That the flue exit can be 150mm (6") despite the riser being 175mm (7") as long as I slide it through the bench and cut a large opening into the flue pipe for a nice sized exit.

Bennen, that seems sound. No reduction of 15%

I can't remember, but is this a batch or J?

One thing i would do, i would insulate the floor. Just to slow the seeping of heat down there.

Hi Satamax, this is batch. Fire box will penetrate the wall there and be fed from the other side.
I was thinking the same this morning. Maybe just drop some super wool on the slab there once the brick is finished.
Possibly line the side wall of slab with insulating fire bricks. That space is only 1sqm though.

Plan is to cast the bench. A friend suggested a cheap Chinese engineered granite bench top as they can be had cheap and apparently used for sauna rocks?

Getting under way. Managed most of the first 3 courses tonight. Tomorrow the 4th course will bridge what is already down onto the upper level of the slab.

Satamax, should you recommend insulating the side wall part of the concrete?  I was thinking of lining with insulating fire bricks or super wool.

Dunno!

I would not myself, It all depends on what heat you can spare. And how much heat you need  in the space where you had the cupboard.

To me, it's un necessary complication.

Just what I wanted to hear!

Benen Huntley wrote:Just what I wanted to hear!

Anyway, heat will go up in the Bell, but lick the wall there, heat it up above the insulation you were proposing to use. Then, since heat travels in all directions in mass. Heat would go back down. You would not stop the floor from heating up. Juste slow down the process. So, i do 't see the point.

I also assume it is OK to use clay pavers and regular mortar for the entire bell due to the fact that much heat will be extracted by the steel portion of the bell around the riser?

Well, from the experience from my own stoves. I would say yes. My workshop  heater barrel, reaches 230c° .  so, up to 400c° i think things are fine.

It's coming along well. The top row of bricks is the height that it will end up plus the top obviously. He fire box and steel drum will sit as close to the flue pipe as possible to keep the profile down and hopefully the drum roll heat the flue pipe some and assist with draw.

Here is a sketch up of the core design I've quickly come up with.
all 75mm fire bricks for the fire box and for the riser up to the fire box height. The remainder of the riser I think I'll give the superwool inside flue pipe trick a go.
I was hoping ideally to lock the riser bricks into the fire box bricks rather than have them stacked against each other but will probably just extend the top row over the fire box by 50mm or so as shown in the file. Although that may do very little without extra weight above i suppose.

Bell is mostly complete!

Bennen, on the corridor side,  do a double layer of bricks, to stop cracks, and risks of smoke leaks.

There's not much room there at all for another row of bricks. About 40mm at the absolute max before encroaching on the walking space. Perhaps there another solution than another row of bricks that would be suitable? A sheet of fibre cement board maybe?

Spent some time pulling the tank out of an old 300l hot water service this afternoon. Needs to be cut to about 1000mm tall to clear the riser by 30cm. The brick part of the bell will need to be slightly reduced in ISA to stay at around 7sqm.

Stuff like fermacell should do the job, sure.  

I don't know how much would be your increase in isa. But since you're using a plunger tube, there is a trick. You make your plunger tube adjustable depth wise,  so you can fine tune your draw.  Easy to do, and you don't have to mess about with your clean looking "plan"

Ah you're amazing. Such a great idea. Just raise the exit height!

I will take home some melamine chipboard tonight to build the form for the top. If regular mortar is fine for the brickwork then regular concrete should be fine for the top.
Did you have any advice here? Would you add petite or vermiculite to make it lighter?
Without reinforcement bar will I have integrity issues? The span is only 40cm.

Well, i wouldn't play with concrete, nor rebar for the top.

I know it won't be that hot. But that's the part which will take the bulk of the heat the fastest. To me, it's refractory poured with stainless needles. Or refractory "pavers"  I've checked ebay.au. Nothing!


May be this https://www.bricksblockspaversonline.com.au/refractory-slab-300x300x50mm-p228/

with a T bar for holding their weight in the center.

Or somethink like this

https://www.sydneyfirebricks.net.au/shop/mortars-castables-insulation/20kg-refractory-castable-1350-degree-2/

1350C°, that's a plenty.

Over here, i would use mapegrout refractory. But i doubt you can have some there.

https://www.ebay.com.au/itm/5-lb-Ribtec-Fiber-Refractory-Reinforcing-3-4-304-Stainless-Steel-Needles-Cement/232347907661?hash=item361903b64d%3Ag%3A6-sAAOSwsXFZJb-R&_sacat=0&_nkw=stainless+steel+needles+reinforcing&_from=R40&rt=nc&_trksid=m570.l1313&LH_TitleDesc=0

Should have waited for a reply. I just spent $40 on timber and built this haha.

I can get buckets of refractory cement at a wood pizza oven place not far I believe. I'll look into it

A little word of advice again.

Make that, 3 or 4 pieces, so you can lift theses by yourself, of two persons. And if one cracks, you don't have to replace the whole thing. make the joints between different slabs with superwool or rockwool.

That top piece is meant for the bench, yes? In that case it would be better to do two layers, no rebar, seams overlapping and clay mortar in between. This way, it's much easier to make the thing gastight. Something along the lines of the Mallorca build, as shown in the video.

I see! Cast them 25mm thick to keep it to 50mm?

I did find this. Seems to fit the bill.
I'd need 6 bags j believe. Which would be $330 plus freight.

Any suggestions for a budget option if we don't sit on it. We could always replace it later if things are working well.

Benen Huntley wrote:

Any suggestions for a budget option if we don't sit on it. We could always replace it later if things are working well.

Well, carry on with your idea of covering it with normal concrete. But put a metal plate underneath. A piece of 2mm steel, the right length and width. You could even support the whole complex of metal and concrete with three crosswise T bars. Tho, remember, that theses should not be mortared in. and have expansion space lengthwise. Usually, you fit these in slots cut into the bricks, filled with a bit of superwool or rockwool.

The top of the bench doesn't need to be refractory concrete, in my own opinion.

The bench top of the Mallorca build was two layers of a very weak and thin cement/sand paver, meant as a cheap alternative for soft locally quarried slabs. In the Netherlands there are concrete sidewalk pavers of 60x40x5 cm. I know of several builds where two layers of that kind have been used. And a couple of others that have one layer of the said pavers and a top layer of sandstone slab, which looked fabulous to say the least.

Heat load put to these bench tops are within reasonable safety margins, estimated about 150 ºC at the inside. In 2009 I ran tests with a bell top made of those concrete pavers, inside temperature never went over 400 ºC. I have to add, the top gap of that bell was over a meter and the core was a smallish 13 cm J-tube. Benches are perfectly safe with a top like that, no problem I would say.
see https://donkey32.proboards.com/post/232/thread

Weight load of such a two-layer solution is far beyond the weight of human beings.

Satamax Antone wrote:Well, carry on with your idea of covering it with normal concrete. But put a metal plate underneath. A piece of 2mm steel, the right length and width. You could even support the whole complex of metal and concrete with three crosswise T bars. Tho, remember, that theses should not be mortared in. and have expansion space lengthwise. Usually, you fit these in slots cut into the bricks, filled with a bit of superwool or rockwool.

Max, it isn't often that I feel I urge to contradict you, but this is one of those occasions. Benen is building an RMH with a steel bell and a bell bench as far as I am aware of. The chance that you'll be able to crank up the inside of such a bench up to over 400 ºC is fairly small, if not impossible. A steel plate under the bench top would expand much quicker than the pavers above it, so the bench would develop cracks for many years to come, over and over again. When you meant to say that the pavers should span the depth of the bench in one go, I agree.

Peter, what i mean is, steel T's tucked into the bricks, with an expansion gap.

Heat induced metal creep is around 600C°, i doubt it will reach that.

Then a layer of superwool, flat on top of the bricks.

Then the sheet metal over that, to me it's just an easy way to "airtight" the top of the bell. Then pavers or whatever he likes above. Providing one edge of each of these is laying on the metal above a row of bricks.

The top is free, able to expand and contract, but the weight of the pavers keeps the joint tight.

This is for the "just in case" exceptional situation, where the top of the bench would reach more than 400C° which is normal concrete spalling temperature.

I didn't imply, by any means, to mortar the metal plate!  

Steel could really work well for me. The steel bell could rest on a few welded on tabs once penetrating the concrete bench. Then I can just cast the top in a couple of pieces and if it cracks it's no big deal as the steel will keep the seal.
Also seems easy, convenient and cheap!

Just to confirm, a 150mm flue will be fine for a 175mm batch rocket? I may cast the top tonight or tomorrow!

Will use an off cut from the steel bell and a piece of flue pipe to leave the holes in the correct locations.

It's up to you to take the decision.

I have done things like this before. But, sometimes they don't work.

175,mm has a CSA of 240.52 cm²

and 150 mm  has a csa of 176.71 cm²70 square cm less or thereabouts.

To me that seems a lot.

In my workshop heater, i run a 220mm round riser batch, dimensioned right, into a square 200x200, with rounded corners. Which might not be that far off.

It's true when you put it like that. It is a lot.  

I cut the bricks that I had on hand today. She's not pretty from the side due to the brick layout but the riser is nice which is what matters! I decided to put in the extra effort and cut bricks to make the riser lock into the fire box also.
Port ended up being 59mm rather than 50mm but not a problem I think.
I need to collect another 24 bricks for the fire box walls and the floor to finish it.

From here a plate will go on top with a hole over the riser to insert the insulated flue pipe riser.

Will probably enclose the entire core in a steel box and slide it through into the bell and seal the edges.

Benen, i would remove the two angled bricks behind the port here.

https://permies.com/t/90336/a/63791/thumb-IMAG0818.jpg

To create low presure areas behind the port, so the ram horns form better.

Nice video! Do you mean the 45 degree cut at the back. So it looks more like this?
But only the 3courses of brick at the port level?
The 2nd course is like this. The other two would need adjustment to the bricks. But no problem.

Well, i see the problem!

I prefer it that way, flat behind the port, to increase the depression zone. I wonder what Peter has to say. It might not be that important. It's just old studies, about mechanics, and a smidge of fluid mechanics, which makes me think this way.

Yes, it can be done like you suggest, Max. I updated the site a week ago with this article about riser simplification. All the other editions are on hold until Terry is ready with correcting the English side of it. Bar the Dutch version, but I have the gut feeling that one isn't useful to you.

I see..
These things always come up after I build the hard way haha.
Should be quite easy to cut the chamfer out from behind the port at least.

It looks like I should also exclude the ramp if I understand the article correctly.

Have been away for work for a bit but I'm back into it again. Cut the water heater to size today. Looks to Ben 4mm thick. I can get steel in 3mm to weld a lid onto the thing which I'll do tomorrow.
ISA is 2.265sqm.

It has been some weeks since I had time to work on the heater! Today we cast the top of the bell.  

Flue pipe was tough to get out but it worked a treat.

9 months later and I remember it can get cold in Australia haha. Today we started the wall penetration. I also have all the steel necessary to build a door and a box to contain the core.

Good progress the last two days. Have completed the firebox. All that's needed on the door is some system on the back for holding in the glass and some hinges.
I spent a lot of time grinding the welds ready to paint. They look rough in this light but they came up very smooth and will look good once painted I think.
Tomorrow it will be located in the bell and the bricks assembled inside.
The image of the door makes it look like flat steel but it is laminated to 40x40x2mm square tube around the perimeter.