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Rockhopper

Pros/Cons: 2-1/2" vs 3" brick? (Firing ^6)

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I am shopping for a new (or, at-least new to me) kiln.  My JW Good manual kiln was severely damaged when a large walnut tree fell on my garage.  On the plus side, I get a new garage - and a new kiln.  On the down side, it will probably be at-last 3 months before the new garage is finished and I can fire anything. 

I'm considering a brand-new kiln, as I'm finding it hard to find decent used ones that are offered at prices far enough below the new to make it worth buying used.

I'm looking  for a relatively small ^8-^10-rated kiln, that I plan to fire at ^6.   Something in the 3 cu.ft. range - such as the Skutt KM-822.  It looks like the 3" brick isn't much more expensive than 2-1/2" ($75 more on the Skutt), so not really a big factor cost-wise  - but I do wonder how long it would take to recover that $75 in reduced electricity cost - when I'm currently only firing 4-5x/year.

I saw a recent comment from @neilestrick in another thread, that says in part "Thinner brick use slightly more electricity, but they cool faster....  L&L's most powerful kilns, the JH crystalline series, are rated for cone 12, but are built with 2.5" brick. The thinner brick allow for faster cooling times, and more precise temperature control."  - which sounds as though the 2.5" may actually be better (or maybe it's just a non-issue with the volume I fire).

The other aspect of the brick thickness I'm looking at is interior dimensions:  Not so much in terms of capacity - but with regard to 'open space'.  Does the amount of space between edge of shelf and brick have any effect on firing ?   Assuming I'm using a 15" shelf, centered in the kiln, we're talking about 1.5" all around vs 1".   The extra 1/2 inch of finger space between shelf and brick when loading/unloading might be nice - but would it possibly make any difference in even distribution of heat within the kiln ?

Edited by Rockhopper

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53 minutes ago, Rockhopper said:

I am shopping for a new (or, at-least new to me) kiln.  My JW Good manual kiln was severely damaged when a large walnut tree fell on my garage.  On the plus side, I get a new garage - and a new kiln.  On the down side, it will probably be at-last 3 months before the new garage is finished and I can fire anything. 

I'm considering a brand-new kiln, as I'm finding it hard to find decent used ones that are offered at prices far enough below the new to make it worth buying used.

I'm looking  for a relatively small ^8-^10-rated kiln, that I plan to fire at ^6.   Something in the 3 cu.ft. range - such as the Skutt KM-822.  It looks like the 3" brick isn't much more expensive than 2-1/2" ($75 more on the Skutt), so not really a big factor cost-wise  - but I do wonder how long it would take to recover that $75 in reduced electricity cost - when I'm currently only firing 4-5x/year.

I saw a recent comment from @neilestrick in another thread, that says in part "Thinner brick use slightly more electricity, but they cool faster....  L&L's most powerful kilns, the JH crystalline series, are rated for cone 12, but are built with 2.5" brick. The thinner brick allow for faster cooling times, and more precise temperature control."  - which sounds as though the 2.5" may actually be better (or maybe it's just a non-issue with the volume I fire).

The other aspect of the brick thickness I'm looking at is interior dimensions:  Not so much in terms of capacity - but with regard to 'open space'.  Does the amount of space between edge of shelf and brick have any effect on firing ?   Assuming I'm using a 15" shelf, centered in the kiln, we're talking about 1.5" all around vs 1".   The extra 1/2 inch of finger space between shelf and brick when loading/unloading might be nice - but would it possibly make any difference in even distribution of heat within the kiln ?

You probably won't get the precision benefits unless you have a very powerful kiln that can react quickly to keep temperatures steady, and you would need a type S thermocouple to really get the benefits. And unless you're doing crystalline work, none of that is necessary.

Typically you would use a shelf that is sized to the chamber dimension, like a 15 1/2" shelf for 2.5" brick or a 15" shelf for 3" brick. 

If the kiln is indoors, the 3" brick will radiate less heat and keep the space more comfortable and make it cheaper to cool in the summer.

Just get the 3" brick if you're buying new.

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are your current shelves going to be used in the new kiln?   if so, check that finger width spacing.   with gloves on, it is sometimes hard to get fingers under the shelves in my 3 inch brick kiln.

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Was hoping to use my current octagon shelves.  They would work OK with 2-1/2" brick, at 17-1/2" inside measure  - but with 16-1/2" ID for the 3" brick, I would probably have to get new shelves.   They were labeled as 15-inch, but actually measure closer to 15-1/2".  I'm thinking in order to have comfortable finger room for loading/unloading, I would want an inch all around - which would mean a 14-1/2" flat-to-flat octagon if I go with the 3" brick.  

That's why I was wondering what the 'payback' time would be for the energy savings of the 3" to offset the increased cost.  And, since my original post, I've realized that if I go with the 3", I would have to factor in the cost of new shelves, in addition to the higher price of the kiln itself.

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I like my 3 inch kiln, very nice.  My shelves are 40 bucks a piece so not exactly cheap, but overall a small price to pay.  As far as a specific energy savings on that extra half inch... No idea.  Seems weird to me that the inside of the kiln would be a smaller diameter with the thicker brick, I thought a 23 inch kiln is a 23 inch inside diameter regardless of brick size, is that not the case?

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Some years ago our school studio upgraded to new 3" brick kilns but kept the shelves from the  old 2.5" brick kilns. We use only half shelves so we were able to make it work by allowing the inside straight edge of the shelf to slightly overlap the centerline  and load so that the half shelves never were at the same level. Your specific situation may be different.

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1 hour ago, liambesaw said:

Seems weird to me that the inside of the kiln would be a smaller diameter with the thicker brick, I thought a 23 inch kiln is a 23 inch inside diameter regardless of brick size

At-least with the kilns I'm looking at (L&L e18T / e18T-3, Paragon TnF82 / TnF82-3, & Skutt KM822 / KM822-3), they seem to keep the outer dimension the same, rather than the inner.  I'm guessing this is so they can use the same outer jacket, and lid-band regardless whether 2-1/2" or 3" bricks are used.

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1 hour ago, Dick White said:

We use only half shelves so we were able to make it work by allowing the inside straight edge of the shelf to slightly overlap the centerline  and load so that the half shelves never were at the same level.

Hmmm...   If I wind up getting the 3" brick, and new shelves, I'll have to look at half shelves as an option.  Of course, that also means I would need to get some more posts, since it takes more for two half-shelves than for one full shelf.

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7 minutes ago, Rockhopper said:

At-least with the kilns I'm looking at (L&L e18T / e18T-3, Paragon TnF82 / TnF82-3, & Skutt KM822 / KM822-3), they seem to keep the outer dimension the same, rather than the inner.  I'm guessing this is so they can use the same outer jacket, and lid-band regardless whether 2-1/2" or 3" bricks are used.

Also, the bricks are cut with very little waste. 2.5" bricks set the standard decades ago. They wouldn't be able to make the outer dimension larger with the same 9" long brick.

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