Is A Square Cross Draft Kiln More Efficient?

[jrgpots]

I was reviewing kiln construction in The Kiln Book by F. Olsen.  He states that a cube shaped kiln is most efficient.  I have plans to build a cross draft kiln with inner measurements of 14" deep x 30 " wide x 24" tall.  The arch will be across the width of the kiln. This should allow one 11 X 22 shelf or two 11 x 11 square shelves.  The 2 burners will be on one side wall and the flue on the opposite side wall.

 

1.  Will this shape work?

2.  Will this shape have inherent hot and cold spots?

3.  How much harder (and more costly) would this shape be to fire than the standard cube?

 

Jed

[Mark C.]

Jed,

1st the cube is perfect world theory . That said its a good guide line.

I'm not a cross draft fan with the exception wood firing .John is the expert on this area

The reason  for more burners is if you have 4 corner up thru the floor or 4 burners two on each side the temps are more even to start with.

As to your 11x22 shelve which is fine size you also need a bag wall and combustion space.

My car kiln is 44 wide 46 deep and 51 high with a sprung arch over that

my small updraft is 27 x28 deep x33 h with a sprung arch on top

These all have the cube feel to them just not exactly a cube

your 14 inch plan is a bit narrow now 28 x 30 x 24 would be a better  cube size.

You do build a kiln starting from your shelve size 1st or I do.

if its a small kiln you want how about a burner on each side and a downdraft exit in rear with your11x22 shelve running down the chamber front to rear with small bag walls on each side?

even heat good flow thru and down drafts fire even usually.

[Marcia Selsor]

I have designed and built downdraft kilns during my career teaching ceramics at the university level. I always considered designing them to the size shelf you can handle. 12 x 24 was a good standard and 24 x 24 was a good floor plan. Larger for car kilns, various configurations for catenary arches.

Is a small kiln efficient in the long run would be a good question to ask?

For the burner placement, I'd put it next to the flu with a 4.5" -9" bagwall and a target brick at the opposite side on each side of the door but below the first shelf level.

Marcia

[neilestrick]

So, a layout like this image- burners on left, long shelf, exit flue on right? Would do it the other way- turn the shelf so the burners are coming in along the long side of the shelf, leave 9" or more for firebox and bag wall.

 

[Mark C.]

As in Neils diagram I to would have the burners coming in on the long side one on each side as I noted in my post  above (or thats what I meant if it was not clear ) the exit flue on one end the door on the other end.

[jrgpots]

How does this work?  kiln's interior foot print is 30" x 24".  This gives an 8" deep firebox.  Two 11' x 22" shelves sit side by side.

The burner ports are 4" x 4"  and the flue 6" x 6" which could be 8" x 8" easily. walls are 8" hard brick and 2.5 soft brick liner.

 

 

Jed

 

[jrgpots]

For the burner placement, I'd put it next to the flu with a 4.5" -9" bagwall and a target brick at the opposite side on each side of the door but below the first shelf level.Marcia

I made two 1.5 inch diameter power burners for the kiln. I guess I can make two more. Each burner nozzle is drilled to 3/32". At 14 WC of pressure the 4 burner configuration gives me 23,090 BTU/cu ft. That will work.

 

Jed

[Mark C.]

I'm not a cross draft fan for all the reasons I mentioned I above

Is there some pressing reason you do not want burners on opposing sides?

[jrgpots]

I'm not a cross draft fan for all the reasons I mentioned I above

Is there some pressing reason you do not want burners on opposing sides?

Marcia's and your post make me think about 2 burners on each side is best.

 

Jed

[jrgpots]

Now a silly question...If I make burners on both sides, do I need a firebox and bag wall on each side? If that is the case, my 30" wide foot print translates into shelf space of 16".?

 

Jed

[Mark C.]

First Marcia said she likes the burners(2 in this case) in the rear next to flue shooting down a bag wall with a target brick(thats a brick that splits the flame. If your planning on forced air burners I have zero issues and agree with that. I do not think you have mentioned what type of burners other than power (forced air??).

I'm a natural draft man so my burners I like to come into the side of kiln and hit the bag wall gently .

so it depends on the burner to some degree.

To answer your question on bags walls on both sides thats a yes

This next part is with standard bricks and if I recall yours are not that but lets say they are  to figure this so-

The way I figure your 30 inches-minus 4.5 for combustion space x2=9 the bag wall is 2.5x2=5 inches total 14 inches minus the 30 leaves 16 inch an odd side at best.This needs to be sized a bit different. For a one shelve kiln  with only two burners the combustion area could be cut down some

your burner ports could be 4.5x 4.5 and the flue on a small kiln your 6x6 will be fine you can always brick down a flue.

 

I only build myself with 12x24 shelves but that because they are standard for my work and most potters I know have that size as well. I have always bought and used that size. I do have a few larger and smaller ones but use them little.

I think you still need to keep planning a bit. Decide how many shelves to use and what size (do you already own some?)

they go from there.

[Marcia Selsor]

I'll do a diagram. The target brick shoots the flame up not splitting it. sorry for not being clear on that.

I built burners for a larger kiln and added Grainger squirrel cage blowers although it ran on propane.

Others ran on natural gas.I would add that designing a kiln should be by brick size as mark is saying. a standard brick is 4.5 x 9 x 2.25. I have the old AP Green manual that includes arch layout, spans , rise etc

I love building kilns and then firing them.

Kiln should be double wall of bricks or very well insulated with fiber. I fired this type of kiln for 20 years 1-2 x per week after the third week of the semester. Also had a car kiln firing as frequently.

This kiln fired evenly if stacked the way it liked it. : dense in the front and lower back and tall pieces in the top rear.The shelves were sitting ON the bagwall. A center post was in the front and back leaving a space for large bowls or platters if needed. Oops I left out three courses of floor bricks on the drawing.

Having my second espresso now.

 

Marcia

[Mark C.]

I,m on my lunch expresso now and will ask about your brick dimensions and how are you planing the wall in cross section

When you said 2.5 Insulation brick are you planing on stacking them on edge? And if so how will you stablelize them?

[jrgpots]

OK, I have 2 rows of super duty (weird-shaped 4x4x11.5 tongue and groove bricks) stacked side by side staggered joint for an 8" thick outer wall. Then I was going to stack the IFB on its side for 2.5 " liner. I thought about mortoring the IFB. But I bet you are going to tell me that I need to stack them flat giving a 4.5" liner...

If I stack the IFB flat, my wall will be 12.5" thick with the inner 4.5 inches of IFB. I don't know how to interlock or secure the IFB to the hard brick. Or should I?

I could just have 8" walls Of the super duty brick without the IFB.

I'm open to all suggestion except the obvious one which would be, "get all standard sized brick."


Jed

[Mark C.]

I see issues with the soft brick on the narrow edge stacked like that unsecured. With heat it will move ,bow and be a problem down the road.

I have only ever worked on one kiln with a layer like that and it was held under pressure with clamps and was only 2.5 thick backed with 2 inch of fiber.

If you have the soft brick I would lay them down on the flat side-thicker walls will  not hurt . If you are short on soft bricks-I know you have plenty of those odd hard bricks .Another option is pin a 2 inch layer of ceramic fiber on the inside of the hard brick and forget the soft brick  and use a roll of High temp 2,600 degree fiber is under $200 on e-bay.Hi-temp carries it on e-bay.

[neilestrick]

I would not use the soft brick stacked on their sides. They won't stay put. When using both types of brick you need to run a course that ties them together every 5-7 rows. I think you can do a 4.5" soft brick inner row with a 4" hard brick outer row and be fine. You're only half an inch short of normal there. Fiber is a mess. Avoid it if you can.

 

I would go with Marcia's design if you need both burners and want to use a single shelf. If you don't have enough bricks for that, go with bringing the burners in on the same side, opposite the flue, along the long side of the shelf.

[Mark C.]

Since his hard bricks are extremely unusual size I see tying them together as nearly impossible (he sent me a piece of one of those bricks)

Thats why I suggested the fiber.

You may what to stack some up and see if they come together in 3-6 layers so then you could ty the courses-

Again his hard bricks are very unusual -what is their thickness?

This is the trouble with specialty bricks-thats why I have learned to avoid them

[Magnolia Mud Researdh]

Jed,

Take a look at the design of the MN flat-top kiln created by Nils Lou, Mel Jacobson, and Kurt Wild. 

It is one of the most efficient and simplest studio kilns you can build yourself.

It does not need bag walls, arches, tall stacks, etc. 

The PMI article:
Building a Small Flat-top Kiln
By Mel Jacobson and Kurt Wild

March/April 2005 • Pottery Making Illustrated

There is a pdf of the complete plans showing a brick by brick layout of each piece. 

If you are a PMI subscriber you can get it from their website. 

If not send an email to Mel Jacobson.
 

Also, you should read Mel's book: 21st Century Kilns
It is available from his website: http://www.melpots.com

 

LT

[bciskepottery]

FlattopKiln_Complete- mel's in PMI.pdf

 

 

Jed,

Take a look at the design of the MN flat-top kiln created by Nils Lou, Mel Jacobson, and Kurt Wild. 

It is one of the most efficient and simplest studio kilns you can build yourself.

It does not need bag walls, arches, tall stacks, etc. 

The PMI article:
Building a Small Flat-top Kiln
By Mel Jacobson and Kurt Wild

March/April 2005 • Pottery Making Illustrated

There is a pdf of the complete plans showing a brick by brick layout of each piece. 

If you are a PMI subscriber you can get it from their website. 

If not send an email to Mel Jacobson.
 

Also, you should read Mel's book: 21st Century Kilns
It is available from his website: http://www.melpots.com

 

LT

 

FlattopKiln_Complete- mel's in PMI.pdf

[jrgpots]

This week has been heavy at work and I have neglected updating the posts.  In one day I dealt with 1 heart attack in progress, 1 heroin overdose, one family fight, and one loose post-operative cow from the animal hospital behind my clinic in addition to the "normal' patients. It was a freaky Friday.  

 

Thanks for the plans LT and bciske!.  

 

1. Neil, I think I can tie the IFB liner to the hard brick.  As Mark mentioned, my hard brick have character.  They are 4 x 4 x 11.5 inches.  They are tongue and grooved on 4 sides.  The bottom is flat.  The top is flat except for a 3/4/ in deep and 3 in long datto  cut out at one end of the brick.  This datto cutout i s just the same thickness as a kiln shelf.  I can cut pieces of kiln shelf that act as anchors from the soft brick to the hard brick. ( I'm not sure if anyone is following what I am trying to say.)  But the point is every 11.5 inches on the hard brick course, I can tie into the IFB 

.

2. Marcia I love the plan and will use it as the basic shape of my monster.

 

3. I think I will have 8 inches of hard brick (2 brick thick) and 4.5 inches of IFB liner.  My walls will be 12.5 inches thick. the floor will also be a sandwich of one layer of IFB between two layers of my hard brick. 

 

4. Mark, I have one shelf that is 11 x 11.  So right now I will be buying all new shelves.  I am not therefore still open to all different size combos. You said you like 12 x 24.  Is that more standard than the 11 x 22?

 

5. I don't know if I should use castable or arch bricks for the arch.  

 

6. I have about 90 sq ft of 2" fiber wool I salvaged from an old kiln, But hesitate to use this as a liner.  I may end up using some of it for the door.

 

tomorrow I will lay out the basic shape one the garage floor of my latest  version and take pictures.  

.

Thank you for the feedback

 

Jed

[Mark C.]

This week has been heavy at work and I have neglected updating the posts.  In one day I dealt with 1 heart attack in progress, 1 heroin overdose, one family fight, and one loose post-operative cow from the animal hospital behind my clinic in addition to the "normal' patients. It was a freaky Friday.  

 

Thanks for the plans LT and bciske!.  

 

1. Neil, I think I can tie the IFB liner to the hard brick.  As Mark mentioned, my hard brick have character.  They are 4 x 4 x 11.5 inches.  They are tongue and grooved on 4 sides.  The bottom is flat.  The top is flat except for a 3/4/ in deep and 3 in long datto  cut out at one end of the brick.  This datto cutout i s just the same thickness as a kiln shelf.  I can cut pieces of kiln shelf that act as anchors from the soft brick to the hard brick. ( I'm not sure if anyone is following what I am trying to say.)  But the point is every 11.5 inches on the hard brick course, I can tie into the IFB 

.Yes do that 

2. Marcia I love the plan and will use it as the basic shape of my monster.

 

3. I think I will have 8 inches of hard brick (2 brick thick) and 4.5 inches of IFB liner.  My walls will be 12.5 inches thick. the floor will also be a sandwich of one layer of IFB between two layers of my hard brick. 

 

4. Mark, I have one shelf that is 11 x 11.  So right now I will be buying all new shelves.  I am not therefore still open to all different size combos. You said you like 12 x 24.  Is that more standard than the 11 x 22?

for me and  most all the potters I work with 12x24 is the standard but some kiln manufactures use smaller sizes.

it all depends on your end game-mine and those I know make our living with pots and that size fits most all pots even our large bowls(think about your pots feet) smaller shelves= smaller pots feet size

5. I don't know if I should use castable or arch bricks for the arch.  

Bricks are my favorite as they expand and contract no issues. I have had issues with castles -they can work fine just need to be right application and right form etc.

6. I have about 90 sq ft of 2" fiber wool I salvaged from an old kiln, But hesitate to use this as a liner.  I may end up using some of it for the door.

Never think about used salvage fiber as a kiln liner-get NEW 2,600 degree or better fiber for liner in a high fire kiln use that old stuff as outer casing raku kiln or wrapping only trash can or some other light duty use-

tomorrow I will lay out the basic shape one the garage floor of my latest  version and take pictures.  

.

Thank you for the feedback

 

Jed

[jrgpots]

I'm thinking about using the fiber around my conversion kiln.  I will take off the stainless jacket, wrap the IFB, and put the jacket back on loosely.  Then my little kiln can reach cone 6. Maybe..

[neilestrick]

I'm thinking about using the fiber around my conversion kiln.  I will take off the stainless jacket, wrap the IFB, and put the jacket back on loosely.  Then my little kiln can reach cone 6. Maybe..

 

In order for the jacket to hold the bricks together, you'd have to tighten it up so much that the fiber would compress and negate any benefit to having it there. If you want to go that route, you'd be better off using rigid fiber board.

[jrgpots]

.... you'd be better off using rigid fiber board.

 

Would not have thought of that. Thanks

 

Jed