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High Bridge Pottery

Kiln Conversion Updraft Downdraft Chimney?

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I am getting a burner :D happy days. I was informed that it goes from candle to burning paint off the wall at 10 metre. Said I would be getting I think 45,000 BTU at 3 psi. Venturi. Comes with everything needed except the gas tank. Kiln is 5.05ftI got 60,000 BTU for the kiln but supplier said he thought less was fine.

 

I really want a downdraft kiln, but is it worth it? I have a bias towards them from research.

 

Seen Simon Leach kiln with the chimney inside but could I work one outside? The chimney would go out the base/side (not sure yet) and I would have a better divider in the middle that is not taking up so much space.

 

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Ignore the very wobbly chimney stack  :lol:

 

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In a kiln that small a downdraft would do wonders to help even out the temperatures. I'm sure you've seen all the threads here on the forum about the troubles people have keeping the round updraft kilns even.

 

You biggest problem will be getting the stack to fit tight with the wall of the kiln. Any gaps will affect the draft. I would think about cutting away part of the steel jacket on the kiln and weaving the chimney bricks into the wall bricks at the flue opening or at the very least having the chimney bricks fit inside the wall bricks, not just butted up against the outer surface. The chimney could run horizontal for a brick or more before going vertical, so the chimney can be framed/stabilized independent of the kiln body. It won't be portable, of course, but you want to get the tightest fit possible so as not to spoil the draft.

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Yes I have seen many posts about updraft being very uneven. I will have to get myself something to cut the bottom of the jacket, no tool like that in my box. It would be great if it was portable. I have a stand that could possibly hold the kiln and bottom of the stack with a removable chimney piece? Maybe too complicated. I might be able to make the stand even bigger and have it all on wheels. I live right next to a metal fabricator who would easily modify the stand.

 

I need to be able to move it in and out of the garage.

 

Thanks for the tip about making sure it it a snug fit all round. 

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The kiln cement had some weird oil on the top, black/brown. Mixed it back in.

 

Managed to fit the three bricks to the kiln, not sure on the best way to seal it to the kiln. Would be better if it was not that permanent. Still need some way to hold the chimney stack. Might prop with bricks for the first go. Is the a mortar that is easy to remove from brick like one use? Just some clay from the baag?

 

The burner arrived :D need to decide what kind of gas bottle to get...

 

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Cool project. I have an old top loader just like yours that I will one day soon get around to rebuilding. However, this and related threads got me wondering: is it possible to have a kiln which is both electric and gas which works well over time if you only ever fire it in nice clean oxidation conditions? Would love to be able to choose the energy source...

 

Also, I know you have committed to a brick flue but could you also have used fibre? Seems like it would have been lighter and then could have stayed attached to the kiln itself... Thoughts?

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I think you could get fibre to do the job but I wouldn't really want to work with the stuff. If you got some of the fibre ridgidizer or whatever it is called and formed it around a shape that could work. Not sure how long it would last compared to bricks. I do have a little fibre in a bag from removing the two bricks.

 

Is there a reason you would fire gas oxidation instead of electric?

 

Good to know about the kiln cement.

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Put in the exit flue and cut all the bricks for the chimney :D Shelf and hole cutter for burner entry. Looks ok, would like a little more space for the burner.

 

Going to try first without cementing. I would like to be able to dismantle the stack for moving later on. If I properly fit the bricks it might just work, thinking some small fitting from the kiln flue to the stack made out of fire brick to seal the two.

 

Just happened to find a welder who is willing to trade pots for welding the extra ft to the stand to hold the stack.

 

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Put your bottom shelf up higher, but have a wall under it that will prevent the flame from going directly to the flue opening, or cut off one edge of all the shelves to make more of a firebox area for the burner. I would go with cutting the shelves.

 

How big is the chimney- 4.5" square?

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You want to make sure there's enough room for secondary air to be drawn in through the burner port. Don't crowd the burner. It's worth a try as is. You can always open them up later. In fact when you do a first light up of the burner you'll be able to see if the port is big enough or if the flame is hitting the wall around the port. Make sure you've cut away the metal around the port or it's going to get really hot.

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Is there a reason you would fire gas oxidation instead of electric?

 

 

There are a couple of reasons but I am very interested in what others think.  

 

The main reason is that where I am at kiln elements are expensive and their installation is particularly expensive.  Since they will only last for so many firings (while the rest of your kiln will last for ages) one wants to make them last as long as possible.  The easiest way to do this this is by not using them to heat up kilns when you don't have to. 

 

Electric elements with an electronic controller gives very good control, ramp rates, holds, etc. and you often really want/need this when glaze firing.   However, the thinking is that when bisque firing you don't need this kind of tight control, so you could use gas instead, thereby saving your electric elements and extending their life.  

 

Also, I believe that bisque firing with fuel, and particularly the extra ventilation that having a flue implies, facilitates better organic burnout than electric firing decreasing the likelihood of bloating, etc.  For an old school clay recycler and native clay user like myself, that is important as I have seen the problems first hand many times!  (in fact even in brand new clay we have had bloating problems here lately!) 

 

Finally, back to the glaze firing stage, I think that fully matured clay looks different (and IMHO better) when fired in a fuel kiln as opposed to electric, even under oxidising conditions.

 

Thoughts?

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