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tomhumf

Just another electric to gas kiln conversion

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I know this kind of thread has been done many times. I've read lots of them, watched lots of YouTube videos and clayart topics. From this I have learnt there are many problems with this kind of conversion.

I have never fired with gas, but I love the look of reduction glazes and my old electric kiln was nearly dead anyway. Following a recent house move I faced the prospect of a costly electrician bill to install it in our outbuilding, and decided that converting it to gas would be comparable in cost. 

Initially I was going to do an updraft kiln. After reading many uneven firing woes I decided the cost and hassle of building a chimney would be worthwhile. 

I decided to spend a decent amount of money on a burner. I know one burner kilns aren't  as good as 2 but I don't  have money for another one. Mine will fire up to a 10 cubic ft kiln apparently. It has flame failure protection and a needle valve so it should be ok to fire my small kiln hopefully. 

My kiln is 17" width and 22" deep so around 3 cubic ft. So burner is overkill but perhaps I will build a bigger kiln from scratch in the future and I don't want to have to buy more burners. 

After ordering the burner I read this thread which is very close to what I intend to do. 

Joel originally had a very similar burner to mine, although his was 90 degree and mine is straight. 

I'm worried that this doesn't bode well for my success as he totally changed burner setup after failing to reach temp. I do think there might be something in the comments about his chimney size though... So I'm going to press on with a larger chimney. 

I'm hopefully goes to collect some 230x114x76mm insulation bricks next week. I have worked out on paper my chimney setup. 

Things I need to decide now:

1. Do I use 50/50 fireclay and grog mix with some sodium silicate or something else like expensive kiln mortar to stick bricks together. 

2. Burner port placement. There isn't going to be much room at the base of kiln with that chimney opening. Can I have a burner port above the floor shelf? I guess pots directly in flame path would get too hot. 

3. Connecting chimney to kiln opening. This needs to be insulated, so do I use like a 2cm thick strip of kiln brick as a kind of bridge all around the 4 planes of the connection. This would reduce the area of flue but would be worth it? Not sure if that will make sense to anyone? 

I could ramble all day about this, I will probably just keep posting my progress and hopefully someone may be able to help me out of the darkness and into the light! 

Edit: the 114 in image should read 76! 

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Edited by tomhumf
the 114 in image should read 76! 

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Brick motors hold bricks like glue at high temps.

Homemade mortars shrink when dry and do not work as well. You can buy mortars online thru places like e-bay or Amazon these days just make sure they are rated for the temps you are going to. Since the flue will be super hot do not think this area will be cooler for low temp mortars.I suggest motoring the lower section of stack to keep it air tight. The top can be a loose stack-you can wrap it with steel or wire to keep it together and reusable once this setup fails down the road.

Downdrafts should exit at floor lever

Burners should enter near floor level-you need a target brick/bagwall to keep flame from going out flue.

Think about turning the flame up towards the top as it enters kiln and place the bricks so this has to happen.

The more this goes up and then down thru load the better (more even ) your fires will be.

You can check my kiln conversion thread last month to see one way to do this.

(Connecting chimney to kiln opening. This needs to be insulated, so do I use like a 2cm thick strip of kiln brick as a kind of bridge all around the 4 planes of the connection. This would reduce the area of flue but would be worth it? Not sure if that will make sense to anyone? )

Not clear to me but yes you need insulation bricks between the jacket to keep the heat off the metal bands.-it can be a soft brick on its side to save space but the whole stack would also be the bricks on side. 2.5 inches of soft brick is enough for the chimney as you are not caring about losing heat there.

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Thanks Mark. I think my brick supplier does mortar too so I'll try get some off them. Thanks for your other suggestions. I've changed my mind a bit about the chimney, it seems I get a larger flue area by arranging the bricks interlocking, and it will make it fit into kiln better.

Also, ignore what I said about the 2cm bridge thing. I could just put two bricks (cut down to 180mm long) into side of kiln, as in the high bridge pottery link I posted. Then cut the flue opening out of them. That would give a flat surface for the chimney to attach to. 

Would it be ok to have a bag wall that isn't the full height of flue opening? I'm thinking maybe a 114mm brick height bag wall running across kiln with a 45 degree deflector at the opposite wall to push the flame up to roof. The first shelf could sit on the bag wall, otherwise my first kiln shelf is going to be 1/3 way up kiln. Not sure if the flame might take a shortcut though? 

I've penciled the intended sections to cutout at the base of kiln in the image.

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I do not think in metric (except pottery lids) so  for me bricks are 9" long x 2.5 " thigh and 4.5" wade

My Molokai kiln shelve was setting on a 2.5 inch brick which made the flue area 2.5 inch high and about 9 inches wide. The bottom shelve sat on top of that-you could do the same.

The burner can come into the front or side (I favor the front) opposite side of stack. Your round shelve  could be pushed bak towards stack side or cut down a bit with a dry diamond or wet Dimond saw so the bricks fit , so the flame hits the bag wall/target brick and deflects up this may take a few bricks across the front all the way across and up a few layers to keep flames going up not out.This height will be Critical and you will have to experiment to get it right.

Take a look at my kiln building Molokai post

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I think the chimney was some of the problem. A good breeze would make it rise in temps after stalling out. The thermocouple was also reading off by a lot but if I remember, cone8 was not budging. A taller chimney that is actually cemented together would be better. 

The flow of my kiln always seemed off and I think it might come down to my burner being in the wrong place. Using a forced air burner solved most of the issues but I still think there's a flow problem.  Some of it also comes down to needing a bit more air space at the back instead of shelf.

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The biggest problem with these kilns is the lack of open space. You cannot load them like an electric kiln, with the shelf only 1 1/2" inches from the side wall. There's just not enough air movement that way. You also cannot think of them like raku kilns. You can get any cobbled together shim-sham kiln up to cone 04. Cone 10 is a totally different ball game. Consider using a shelf that is made for the next size down kiln, or cut a section out of your shelves to create a firebox on one side of the chamber.

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On 4/29/2018 at 12:07 AM, Mark C. said:

My Molokai kiln shelve was setting on a 2.5 inch brick which made the flue area 2.5 inch high and about 9 inches wide

I did look at your thread, maybe my proposed flue size is too big, it would be around 6" x 6 " with my bricks. And your kiln looks to be a lot bigger. 

3 hours ago, High Bridge Pottery said:

cone8 was not budging. 

Didn't you say in your thread that you got 10^ down at some point though?

Are you still using the kiln or moved onto something else? 

1 hour ago, neilestrick said:

Consider using a shelf that is made for the next size down kiln, or cut a section out of your shelves to create a firebox on one side of the chamber

I have been trying to avoid cutting shelves as I though I would need to spend more money on a circular saw. I just tried cutting the edge with a hacksaw though and I reckon it wouldn't take too long with that. 

Do you think if I just took half an inch off the bottom couple of shelves that would be ok? It would leave around 4" gap on the other side. I really want to fire dinner plates on some shelves and they won't fit if I cut them all. 

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Edited by tomhumf
Grammer

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I got to cone10 easily with the forced air burner but not with the venturi burner. It was a while ago now but I remember none of the cones moving at all, maybe one of the 8's slightly.

 

Still using the kiln but not very much as it has been winter and I haven't had any motivation to fire.

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That's a small kiln for dinner plates. 8 sided kilns are barely big enough for a full size dinner plate even if you're firing electric. Don't think about this in terms of how big you want it to be. Think about it in terms of how big it needs to be in order to function. Then figure out what will fit in it.

You really need circulation around the entire shelf, and every shelf, not just the bottom one. Other than silicon-carbide shelves, you can cut them very easily with a masonry blade on a circular saw. Get the cheapest saw you can, as you'll ruin it with all the dust. Around here you can get them for about $30. You can also put a metal blade on it and use it to cut angle iron for the chimney frame. It's worth the money.

I'm thinking cut a couple inches off two opposite sides of the shelves. One side by the firebox, the other side by the exit flue.

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19 minutes ago, neilestrick said:

I'm thinking cut a couple inches off two opposite sides of the shelves. One side by the firebox, the other side by the exit flue.

Ok, I take your point about the plates. Maybe I'll just have to wait until I build a bigger kiln for those. I've drawn what I understand you to mean, about the location of firebox and flue, is that correct? 

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The kiln was not mine-I just did that as a volunteer . I fired it twice to cone 10 in 10 hours.

It was way bigger than yours but it was really small for me. 

This kiln was on an Island in the middle of the Pacific -I was there for 1 month and left.They are firing it again this May but I have my own real salt kiln here at home made from scratch with hard bricks and its a square firing chamber with an arch.

I made due with very limited resources with that kiln. It will have a short life as its a salt kiln.

Neil summed up most of what I was going to say. You need to cut down this shelves. .

This line is from a 2011 post on conversions( You should expect to loose about 1/3 to 1/2 of your interior space to a combustion chamber)

You are missing a large point with your last drawing

First leave the jacket all the way around on kiln. make the chimney go on the outside all the way-maybe thats your plan but the drawing is not clear on this.

The other is you should have the shelve go against the wall next to flue so heat/flame goes under shelve not around or over the shelve then down into flue. This is key point for better even firing. You need to keep the flame going up then down to front and under shelve.

Your drawing does not show the flue path under bottom  shelve? also you need to stop the flame from hitting target brick and then going straight out flue which it will in this drawing.

You need a bag wall to force the flame up and it needs to be a few bricks high. Your bottom shelve or two -can be smaller than the top ones to a small degree.

You will notice in my conversion the shelve is tight against the flue so no flame can get out above that 1st shelve level it has to go down to floor under shelve to get out. Its a key point with any downdraft. You need this feature . Make a few more drawings and lets see them. 

Edited by Mark C.

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18 hours ago, Mark C. said:

 

18 hours ago, Mark C. said:

First leave the jacket all the way around on kiln. make the chimney go on the outside all the way-maybe thats your plan but the drawing is not clear on this.

Thanks Mark. I was intending to leave the jacket on, just cutting a brick sized hole for flue. My drawing probably aren't clear. 

I picked up my bricks, mortar and propane today and have done some mocking up, bearing your comments in mind. 

For the chimney stack I think I'm going to go with a 6" x 3" internal size. This will mean I'll need to cut some bricks but I can't get a decent size without doing this. In the image of the chimney stack the kiln will be on a metal stand, and chimney will be on blocks. The chimney will be as high as kiln when finished. 

The closeup of brick is the one I'll put at base of kiln as the flue exit. It will be cut down to 7 inches long ( the same length as one  of the 8 sides of kiln). After I put it in, I'll cut away the hashed section to give a 3" x 6" opening. 

In the image of the kiln floor, the bit of wood with arrows represents the burner port opening and direction. The peep hole plugs represent angle deflector bricks to push flames up. The brick with hashes would be cut in half - the hashed section removed. All the props represent the same brick size, there is a 6" opening where the ruler is. This is for flue entry. The bricks are 4.5" tall. The cardboard box shows the location where the exit in wall to chimney would be. 

The image of 1st shelf is a cardboard version of my shelf with 1/2" cut off end and 2" off each side. On top of this on bag when all side, there would be another row of 4.5" bricks, all across kiln. On the other side I could use props? And I suppose I would need a brick under the end of kiln shelf at the bottom of image, to restrict flue access to my intended opening on the left. 

Shelves for rest of kiln could have 2" cut off each side but sat more central in kiln? 

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I think 4.5 inches tall on floor is wasted space for exit flue in this mini kiln-I suggest 2.5 inches  tall

cut your flue exit 2.5 inches high  at floor level and have the flue 2.5x  6 inches wide

have the Botton shelve set at 2.5 inches (same as brick thickness.This is a small kiln. 

also make a metal extension past kiln height as downdrafts need to suck and a taller stack -say another 4 feet will help.

I'm assuming where the cardboard box is is where the flue hole is?

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My bricks are 3" not 2.5".  I could have the bottom shelf at 3", and set my output brick a bit lower, so everything is lined up. 

Will look into extension. Could you just use stainless steel tube used in extraction systems? 

Yes the cardboard shows where the wall brick/ hole will be. 

 

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Ok use the 3 inch bricks and save the 1.5 inchs of a 4.5 brick

yes stainless is best as the coating will last and not burn off like galvanized or steel that will rust but all this can work.

you have plenty of room in the front area as well as the left side you could shift it all left a tad and also use more room in front by cutting less of shelves.

It does not need to be centered  as you need the most room on right side with burner and bag wall

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I got my flue brick cut, which will feed into the stack. I decided to cut away the bottom of the brick so I wouldn't need to cut my kiln floor. So the brick goes in halfway and fits quite nice. I will mortar it in when the kiln is in position. 

The flue brick walls are only about ¾" thick but I'm thinking they should be ok for such a short distance? Otherwise I could mortar on another thin layer of brick. 

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I think it will depend on how the rest of the chimney bricks are stacked around that flue brick. Maybe notch the flue brick into the other bricks.  If you can get the other bricks all around it then it won't matter. If there are exposed sections, then you could have some heat messing with the stainless jacket around the flue opening. I'm not sure I would mortar that flue brick into the kiln body, but rather leave it slip-fit if possible. I worry that it'll crack because it's so thin.

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Hmm, I was going to have metal angle iron on each edge of chimney. The just put wires around the kiln and chimney to pull them together, with this flue brick just butting up against a 6" x 3" chimney opening. But yes that brick is pretty fragile I guess, maybe I'll cut out some of chimney so it will slide over it like you suggested. 

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Yes if you mortar it it will crack-just fit it tight-you could and I would use a spot of ceramic fiber to insulate between the jacket to keep it cool.The stuff is cheap and you only need a little and it can be the 4 or 6 pound not even 8# is needed.

tuck some fiber in the hole space all around brick then build stack as Neil said.

I would not motar the stack to this brick-let it float otherwise it will crack as this is the hot spot -cooling and expanding.

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I've been very busy doing other things recently but have just managed to get my kiln outside and started building the chimney base. 

I have all the materials I need now I think. The base of stack and first couple  of courses will be cemented, but I'll leave the connecting brick loose. 

Hopefully I will be able to get this thing finished in a week or so! 

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I've done a bit of cementing tonight, just the first 2 courses, then started loose stacking the chimney. 

I was hoping to use wire to hold the angle irons in place and keep them tight. The wire has been snapping when I twist with pliers to tighten it. 

Any ideas on tightening the wire without it breaking? 

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