Bell material

Hi all!

I'm about to commence my next build and am gathering materials.
I'm curious if I need to use fire bricks for a certain amount of the upper part of the bell? Or can the entire bell be built from regular clay bricks and fire cement since they are fired at 1100 odd Celsius anyway.

Thanks

Benen

That's true Benen, but the hottest parts of a bell tend to expand during heating up. And contract again while cooling, abeit slow. So there will be cracks developing in a single-skin bell that's fed with a batchrocket, mainly in the upper part above the level of the riser. I've been building a single skin heater a couple of times and I can recommend the method of building with common bricks while there's a lining of firebricks on the inside with an expansion space between liner and wall.

There are two ways to achieve such a partly lined bell.
One is changing to bricks on edge  at the riser's top level so there will be space on the inside to place split firebricks on edge.
The other is do one layer of bricks that are turned around 90 degrees in the horizontal plane so the bricks are sticking out inside and outside. I've used this construction a number of times and it works.

Excellent news!
I have one more question. Is there any problem building the entire bell with bricks on edge? The walls would them be 75mm rather than 115mm thick and would fit the tight space I have much better.
If I have the walls 115 thick then I only have around 10mm of gap between the riser and bell on two of the sides.

Picking up clay bricks for the bell today to start construction!
For the core. The plan is 75mm fire bricks and an octagon riser. Are 75mm fire bricks suitable for the riser also or should they be insulating fire bricks?

Riser fits in well if I cut the bricks like this but requires 96 bricks so will be quite a costly part of the heater.

Quick mock up tonight in the cavity that I intend to locate the heater and the firebox door penetrating through the wall.
I've attached a sketchup file used for the images. Very tight spacing inside the bell but I think it will work. Also the riser will move closer to the center by a small amount.

Hi Satamax and Peter,

Are you able to advise on bricks for the riser? I have heavy fire bricks but should I use insulating fire bricks for the riser instead?

As for the single skin bell, should I expect cracks if I just built everything above the riser from heavy fire bricks? I've experienced no cracking in the core of my smaller heater using these bricks so far.

I'm going to play around today with putting a cavity in the bell in top of the fire box as a cooking area.

Thanks so much,

Benen

Benen;  For your riser, insulating firebrick are the next best thing to use.
The very best riser (if you can get the material) is what is called the 5 minute riser by a fellow nicknamed pinhead.     Ceramic fiber (wool) blanket 1" thick wrapped inside an appropriate sized stove pipe makes for a batch burner proof riser! truly a revolutionary idea in riser construction.
here is an ebay item #  122673528486 ceramic fiber blanket,  24" tall 12.5' long and 1 " thick is $84.00 delivered ... here... not sure down under.   You can make several riser's with that much.

Hi Thomas,

I recall you suggested this for modifying my 4" bbr. Thanks for the suggestion. It certainly looks a lot easier and cheaper. How does it go as far as longevity and maintenance?
Also, I was under the impression that the riser needed to be as smooth as possible to reduce friction?

Benen, i dont know about longevity. But for te smothness inside, it is not necessary. The boundary layer is always sticking to the wall of the heat riser anyways. With pinhead's riser, i think i would do the base in firebricks. Or may be just the firebox back with the port. And it would be a good idea to keep an access to be able to change the riser.

Creating access in the destination will be very difficult unfortunately. Something I only want to have to do very rarely. Perhaps fire bricks for the firebox and nearby bricks and for the bell above the riser, insulating bricks for the riser itself and clay pavers for the bell below the top of the riser.
I collected these for a very good price for the bulk of the riser.

Bennen, i had imagined a metal door, in a bell's face, for easy access. This could fit your situation.

As well as the fire box door?

Benen Huntley wrote:As well as the fire box door?

Yep, to access the inside of the bell.

A bit like this

http://donkey32.proboards.com/post/18913/thread

Picture 2 and 10.

Bennen, you asked my advice.

First of all, you have 10.19 m² of isa. I think this is too much. Can't remember what Peter says on the subject, but i seem to remember 7 to 8 m² for an 8 inch stove.

I don't like single skin bells. So, if it would be mine, i would make a metal bell, lined outside with bricks. Or inside, if you like metal looks. I mean, bricks crack, and it would be better to have a gases tight envelope.  With your bricks on edge, you might be a tad low on mass too.

Can't you take a bit more room, in the back of the heater, to make it deeper?  Narrow bells like this tend to have more of a flowing pattern, than heat layer stagnation in bigger bells. This is the case of single bells, vs double bells too.

As well, if you don't need to heat upstairs, it's better to have a lower bell.

https://permies.com/t/53413/Inexpensive-vacuum-formed-ceramic-fiber

Thanks Satamax!
I'm not sure how I calculated the bell ISA so incorrectly. I was aiming for 9.4 and thought I was on the mark. I'll double check. (Area of four sides plus area of top and remove the area taken by the fire box on the wall it penetrates yes?)
Mass would be around 1500kg in clay pavers and fire bricks on the bell plus the top whichever material it ended up being.

Unfortunately I don't go much deeper as there is a hallway there and this is where a big built in cupboard currently sits.

I also have no upstairs to heat.

It should be no problem encasing the entire bell in thin steel sheeting.

Maybe a different design in a different location would be better

I am planning to make my Bell from Cement Blocks that are lined with 1/2" (13mm) of geopolymer setting.  I will be pouring the "tiles" into molds, and, once cured, adhering them to the blocks with thin-set.  I will use more unset geopolymer as the "grout" thus sealing any gaps between the "tiles".   This is similar to the concept of tiling bathroom walls.

All of the materials are very inexpensive.  The geopolymer is highly insulative and can withstand temperatures above 1600 degrees C (3000 degrees F).

Bennen, i did a rough calc, not removing the  firebox opening or the area bellow exhaust port.

But i think it's too big anyways.

http://donkey32.proboards.com/thread/1822/sizes-single-bell-systems

I don't think you need it to be that tall. So that's easy fix, imho.

What is the material of the walls of the cupboard?

Any chance it is part of a masonry wall?  

Ah right. I was referencing the batch rocket website.

Yes it is masonry. The entire house is brick. The inside of the cavity is rendered which I can remove. The outside is plaster board glued to the render.

A mess while we renovate but the location I'm talking about is on the right. Photo taken from the kitchen.
On the other side (up the steps) there is a hallway with 4 bedrooms.

Looks more like 275x the CSA of the riser rather than 300x. The post is a few years old though. Can Peter confirm which is correct? Would love for it to be smaller for sure.

Steve, will the thin-set handle the heat of the bell? And the cycling of temperature?

Bennen, if it's red brick behind the plasterboard, why don't you remove the plasterboard, and line the old bricks with firebrick splits? That would make a double skin on three walls, already. And save you a bit of space, to make a proper front wall. With normal bricks on edge, lined with splits. So you have a double skin all the way. You could rest the top slab on the splits edge. No problem.

You can lower your bell, make good use of existing mass. As well, any spare heat will be transferred further in the adjacent walls

If you're absolutely sure there is no wood or anything flammable behind the plasterboard, you could even line that with splits.

Definitely nothing behind except painted render them bricks.
Are you saying just use a single bell?
I thought making it long and narrow would not be so good? The space is 2.3m wide and only .58m deep.

A drum that I have is also 58cm diameter. I considered the possibility of a drum feeding into a brick bell.

If isa need only be 5sqm for a 150mm rocket then I'm down to 4.25 if you remove 15% for adding a bell.
Remove 1.85 for the drum and I'm down to only 2.4m for the brick bell.

Alternatively, if it is possible to fit a 200mm rocket then 8.8sqm - 15% is 7.5.
If stack two barrels to get enough height for 1.44m riser in the first bell then I'm removing 3.7 and left with 3.8sqm for the brick bell.
It drops to 3 sqm if I scale the system down to 175mm which would be less of a squeeze in the space.

I had a very quick play with sketchup and came up with this as an option.

This leaves the bell roughly 865mm wide x 1430 tall x 450 deep.

fire box sticks out about 300mm.

Yep bennen, stay on the single bell configuration. I would say. Barrels are uggly. Plus, you don't need direct heat in a corridor. Really, my opinion, get rid of the plasterboard.
Scrape that render, if it's plastic, and line the cupboard with firebricks. Make a wall with brick on edge, in front of that cupboard. Lined with firebricks split again. That would be the cheapest and easiest solution i think. Pour a slab for the top. That you would leak proof with some rockwool or superwool.

Ah I see. With a gap between the clay bricks and fire bricks?
By bell would still be shallow and very wide though. I thought that was an issue?

The hall is open to the dining and lounge at either end of that cupboard so possibly not too bad? Could always put in a ceiling fan.

Bennen, 450 mm depth should be all right.

I would glue the splits to the existing bricks, because splits won't hold on edge by themselves. Except you're really skilled a mason.

The only thing i would make sure, is that the lengthwise expansion doesn't push the existing walls.

What i mean, really, is make good use of the existing three walls, so you don't waste your energy, time and money.

Benen Huntley wrote: The inside of the cavity is rendered which I can remove. The outside is plaster board glued to the render.

Bennen, if it's solid render, unpainted, not plastic stuff, i would even leave as is. The plasterboard would act as a sort of expansion joint, and backing for the splits.

The pile you have gathered, you can use for the front. Tho, i would line the whole bell from the top, two thirds down with firebrick splits, if not all.

I was re checking your sketchup.

I would stop the bell at 1669mm that's 14 rows of bricks, according to what you have drawn.

Lining the whole cavity, with splits you'd need approximately 350 splits, and for the front wall, 140 full bricks.

You already have the front wall ones.

I think I understand. I could push the bell all the way to one side and line against the back and one side of the cupboard and brick the other two sides and line them also.

I'm torn between single and double bell now.

Double bell I already have two drums and it gives instant heat and I could cook on top and I could duct above and draw hot air elsewhere and it gives easy access to the riser.

Single would look a lot neater though.
It would also need to be sidewinder style to fit this way.

Fire bricks are extortionate here. I can get 38mm, 50mm and 75mm and they're all $5aud each.

Bennen, do it full width. I don't understand why you want to shy from that. Single bell. You pour yourself a slab, for the top, which will only rest on top, with a joint made of rockwool or superwool. You make two handles , and lift it once or twice a year.

For the bricks, there must be some guys advertising on the net, as fireplace specialists. Ask them where they buy. There must be some cheaper options than a fiver a piece.

In uk, i've seen a place selling for a squid a piece.

https://www.ibhs.co.uk/split-fire-brick-9-x-4-1-2-x-1.html

350 might be considered bulk, and bought cheaper.

Satamax Antone wrote:Can't you take a bit more room, in the back of the heater, to make it deeper?  Narrow bells like this tend to have more of a flowing pattern, than heat layer stagnation in bigger bells. This is the case of single bells, vs double bells too.

As well, if you don't need to heat upstairs, it's better to have a lower bell.

https://permies.com/t/53413/Inexpensive-vacuum-formed-ceramic-fiber

Maybe I misunderstood what you said here. I thought I couldn't have the bell over 2m wide but only 450mm deep.

Cheapest I can find for 35mm is $4 :-(
Full size I can get second hand for $2

For the riser I'm investigating a couple of options.
One is a ceramic riser from a foundry riser supplier.

The other is the 5 minute riser but soak it in rigidizer to stabilise it.

Thank you so much for your input by the way. I don't express how much I appreciate the discussion.

I didn't say you can't.

But there seems to be some flow in a  tall, long and narrow bell.

http://heatkit.com/research/2009/lopez-rocket.htm

Instead or a more laminar stagnation in a big bell.

But a single bell, no mater how big, has always that  mixing of gases, due to the velocity of the gases escaping the heat riser. So, in reality it doesn't matter much then.

Daft question, could you find a fuel tank, likes the ones i used in my workshop heater?

If you found a 450mm deep, 1.5x2m tank or even a bit smaller, you chuck that against the plasterboard. Bolt it to the wall even.  Plasterboard which will be protected from extreme heat by the metal.

Pile bricks and mortar, or even stones and mortar, left and right of the tank. Face the front with the bricks you have, make a slab for the top, and you're kind of sorted. Tho, i would cut an opening at the top, for the assembly and maintenance. That's the same as with bricks anyway. Also, i wouldn't do a sidewinder.

But a side loader. Easier in my opinion.

http://donkey32.proboards.com/post/16159/thread

Really leaning to the dual bell build at the moment actually. Apart from looks it seems to have a lot of positives and I have almost everything I need except the flue pipe already.
If we hate it recoils always tear it down and build a single bell around the firebox and flue pipe I guess..

Burning barrels in a bonfire tomorrow.
I assume connecting drums to brick bell that height of connection is not critical but csa of connection is very important?

Whatcha mean?

With a double bell. The exit would come from the bottom of the barrel over the riser and a short pipe into the brick bell. On Peters site it enters a bit above half way and then the flue pipe obviously still exits that bell from the bottom like in a single bell.

On mine, i did it slightly higher, but not much than exit.

What's bellow the link between the two acts kind of a single bell.

For example, if you had two bells next to each others, one low entrance in the first bell, a link between the two, on top, and a low exit, the first bell would vaguely act as a bell, but more like a chimney, and the second like a downdraft tube.

Add a bottom link, while retaining the top link, you have a single bell, with a wall inside.

Best practice, is link at the bottom. . But there is also a matter of practicality. If it's not easy to do, a link between the two, higher than usual is fine.

Ah I see! I would have expected a higher entrance into the second bell to be preferable but your explanation makes sense. I'll see what I can do to join as low as possible.
Too windy today to light the fire to burn barrels unfortunately!

Best way to burn a barrel, make it a  pocket rocket and cover it with rockwool insulation. Or glasswool. Held by chicken wire.