EDWIN GOULD on thu 13 aug 98
In vain I have searched for the formula for the height of a chimney above
the arch. I am about 80% complete on a sprung arch, 20 cu ft down draft
kiln. Can someone provide me with the formula?
Edouard Bastarache on fri 14 aug 98
Hello Edwin ,
Frederick Olsen in his book "The Kiln Book" says:
"PRINCIPLE 5
There should be 3 feet of chimney to every foot of downward pull,plus 1
foot of chimney to every 3 feet
of horizontal pull".(Page 60 of the edition copyrighted in 1983)
He means starting at the same level as the bottom(floor of the kiln) to the
center of the arch.
Later,
Edouard Bastarache
edouardb@sorel-tracy.qc.ca
http://www.sorel-tracy.qc.ca/~edouardb/
----------
> De : EDWIN GOULD
> A : CLAYART@LSV.UKY.EDU
> Objet : chimney height
> Date : 13 ao{t, 1998 12:42
>
> ----------------------------Original message----------------------------
> In vain I have searched for the formula for the height of a chimney above
> the arch. I am about 80% complete on a sprung arch, 20 cu ft down draft
> kiln. Can someone provide me with the formula?
Tracy Dotson on fri 14 aug 98
Its easy....9x9" inside and double the hight of the kiln. this works for most
kilns up to 75cu ft. Tracy Penland NC
A.D. on fri 14 aug 98
Well when I built my 18cu ft downdraft I just made the chimney in such a
way that I could just add on to it. also it never hurts to make it too big
since you can always use the dampner to slow down the draw
sirius@inetarena.com
Aaron DeBord
At 12:42 PM 8/13/98 EDT, you wrote:
>----------------------------Original message----------------------------
>In vain I have searched for the formula for the height of a chimney above
>the arch. I am about 80% complete on a sprung arch, 20 cu ft down draft
> kiln. Can someone provide me with the formula?
>
>
Bruce Girrell on sat 15 aug 98
> ----------------------------Original message----------------------------
> In vain I have searched for the formula for the height of a chimney above
> the arch. I am about 80% complete on a sprung arch, 20 cu ft down draft
> kiln. Can someone provide me with the formula?
>
>From _The Kiln Book_ by Frederick Olsen:
"There should be 3 feet of chimney to every foot of downward pull, plus 1
foot
of chimney to every 3 feet of horizontal pull."
Note that this is the total chimney height, not height above arch.
I assume you can do the rest of the math.
Bruce Girrell
Bob Hanlin on sat 15 aug 98
You might think about this. If you flue isn't big enough you can't get the
gasses out of the kiln and you will have problems reaching your
temperature. So size the flue on the large side and damp back.
At 09:23 AM 8/14/98 EDT, you wrote:
>----------------------------Original message----------------------------
>Hello Edwin ,
>
>Frederick Olsen in his book "The Kiln Book" says:
>"PRINCIPLE 5
>There should be 3 feet of chimney to every foot of downward pull,plus 1
>foot of chimney to every 3 feet
>of horizontal pull".(Page 60 of the edition copyrighted in 1983)
>He means starting at the same level as the bottom(floor of the kiln) to the
>center of the arch.
>
>Later,
>
>Edouard Bastarache
>edouardb@sorel-tracy.qc.ca
>http://www.sorel-tracy.qc.ca/~edouardb/
>
>----------
>> De : EDWIN GOULD
>> A : CLAYART@LSV.UKY.EDU
>> Objet : chimney height
>> Date : 13 ao{t, 1998 12:42
>>
>> ----------------------------Original message----------------------------
>> In vain I have searched for the formula for the height of a chimney above
>> the arch. I am about 80% complete on a sprung arch, 20 cu ft down draft
>> kiln. Can someone provide me with the formula?
>
>
Bob Hanlin
bhanlin@ionet.net
Oklahoma City, OK
GREG MARSHALL on sun 1 oct 00
I recently was hired as the pottery instructor at a small college. When =
I looked at the kilns, the first thing that struck me was that the =
chimneys on the two gas kilns were the shortest ones I had ever seen. I =
contacted the previous instructor and asked her how the kilns fired. =
She said that they were uneven with the top being several cones ahead of =
the bottom. My first thought was that the draw was inadequate due to =
the short chimneys.
I've figured how tall the chimney should be on the larger kiln based on =
information in Olsen's "Kiln Book". I would like some feedback to make =
sure I am figuring correctly and to make sure I'm not overlooking =
something.
The kiln is a sprung arch with hardbrick on the outside and softbrick on =
the inside. It fires on natural gas with four atmospheric burners. =20
The dimensions of the inside of the kiln are: 60 1/2" tall from the =
floor to the top of the arch, 45 1/2" wide from wall to wall, and 50 =
1/4" long from front to back. The four burner ports each measure 4 3/4" =
x 4 3/4". The flue opening is seperated by supporting bricks that makes =
two openings that are 5 1/2" x 8". The inside of the chimney measures =
12" x 20 1/2" and the chimney is 8'10" tall from the inside floor to the =
top of the chimney.
Based on Olsen's formula that 3 x dp(downward pull) + (hp(horizontal =
pull) divided by 3) =3D height of chimney I come up with a chimney =
height of 17.05'. I live at 6000' so according to Olsen the chimney =
height should be increased by 30%.
Any help or feedback would be greatly appreciated. Thanks.
Greg at the foot of Pikes Peak
GREG MARSHALL on mon 2 oct 00
Thanks to Margaret and Dave for replying to my question about chimney =
height. To answer their questions, the burners are atmospheric (not =
forced air), and the kiln is a downdraft.
I haven't fired this kiln yet so I really don't have any first hand =
knowledge of how it fires. Another thought I had was that maybe the =
bagwalls were higher than they needed to be. They were 5 brick widths =
high.
Perhaps I should just fire it up and see what happens.
Thanks again.
Greg at the foot of Pikes Peak
Earl Brunner on mon 2 oct 00
I think, unless they have changed, most kiln books seem to
over size the chimneys. I suppose it could have something to
do with the burner arrangements, but Both of my down draft
kilns have had "stacks" either the height of the kiln of
just slightly higher. Both fired very consistently and
within a half of a cone top to bottom, front to back.
One was a kiln I build modifying the plans from two kilns
described in Rhodes' Kilns book (pages 212 and 214), I had
originally intended to make the stack higher on it, but ran
out of brick, I used flue liners on top of the brick at
first, but in the open air they heat shocked and broke. I
put the natural draft burners underneath firing upwards.
That is one of the reasons that I went with my geil kiln, it
was very similar in design to what I had previously built.
Dave Finkelnburg wrote:
>
> Greg,
> You don't say, but I presume from your notes this is a downdraft. Is
> that correct?
> Olsen's advice will get you a chimney that is big enough. In my humble
> opinion, you can make it considerably smaller and it will still be big
> enough. Unless you have a very small flue, you don't need to have the stack
> more than 24-inches higher than the nearest roof peak. Outdoors, that may
> be the top of the kiln. In my case, it's the roof of the kiln shed.
> For your kiln, the cross-section of the flue is already seriously
> oversized. For that kiln 9"x9" should be plenty large enough inside the
> flue.
> Your kiln is a little tall for it's width, which can easily contribute
> to vertical temperature differences.
> I'd be tempted to fire the kiln with a few firebrick and witness cones
> in it before I'd start raising the stack height.
> I hope this helps.
> Dave Finkelnburg
> -----Original Message-----
> From: GREG MARSHALL
> To: CLAYART@LSV.CERAMICS.ORG
> Date: Monday, October 02, 2000 6:42 AM
> Subject: Chimney height
>
> I recently was hired as the pottery instructor at a small college. When I
> looked at the kilns, the first thing that struck me was that the chimneys on
> the two gas kilns were the shortest ones I had ever seen. I contacted the
> previous instructor and asked her how the kilns fired. She said that they
> were uneven with the top being several cones ahead of the bottom. My first
> thought was that the draw was inadequate due to the short chimneys.
> I've figured how tall the chimney should be on the larger kiln based on
> information in Olsen's "Kiln Book". I would like some feedback to make sure
> I am figuring correctly and to make sure I'm not overlooking something.
> The kiln is a sprung arch with hardbrick on the outside and softbrick on the
> inside. It fires on natural gas with four atmospheric burners.
> The dimensions of the inside of the kiln are: 60 1/2" tall from the floor
> to the top of the arch, 45 1/2" wide from wall to wall, and 50 1/4" long
> from front to back. The four burner ports each measure 4 3/4" x 4 3/4".
> The flue opening is seperated by supporting bricks that makes two openings
> that are 5 1/2" x 8". The inside of the chimney measures 12" x 20 1/2" and
> the chimney is 8'10" tall from the inside floor to the top of the chimney.
> Based on Olsen's formula that 3 x dp(downward pull) + (hp(horizontal pull)
> divided by 3) = height of chimney I come up with a chimney height of 17.05'.
> I live at 6000' so according to Olsen the chimney height should be increased
> by 30%.
> Any help or feedback would be greatly appreciated. Thanks.
> Greg at the foot of Pikes Peak
>
> ____________________________________________________________________________
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> ______________________________________________________________________________
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>
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--
Earl Brunner
http://coyote.accessnv.com/bruec
mailto:bruec@anv.net
Snail Scott on mon 2 oct 00
>I live at 6000' so according to Olsen the chimney height should be increased
>by 30%.
>Any help or feedback would be greatly appreciated. Thanks.
>Greg at the foot of Pikes Peak
At this altitude, 'draw' becomes very important. There's less air in the air,
so to speak, so you're possibly right about needing more chimney. Another
option is to adjust your bagwall to direct some flame straight across. If
your burners are horizontal, aimed at a vertical bagwall, try putting a few
gaps between the bagwall bricks. (Small gaps!) This will help heat the bottom
a bit more. You could also try stacking differently; a looser pack at the
bottom
may help even it out a bit. I have fired kilns with worse proportions than
yours
at similar altitudes, with quite even results (after tinkering), so there's
definitely hope. Personally, I would try the easy modifications first before
tackling the chimney.
-Snail
ARTISTINSC@AOL.COM on mon 2 oct 00
What kind of burners are you using as my kiln has 2 blower burners and is a
sprung arch downdraft 45 cuft and has a chimney only 6 feet tall and fires
very evenly.
Margaret
Dave Finkelnburg on mon 2 oct 00
Greg,
You don't say, but I presume from your notes this is a downdraft. Is
that correct?
Olsen's advice will get you a chimney that is big enough. In my humble
opinion, you can make it considerably smaller and it will still be big
enough. Unless you have a very small flue, you don't need to have the stack
more than 24-inches higher than the nearest roof peak. Outdoors, that may
be the top of the kiln. In my case, it's the roof of the kiln shed.
For your kiln, the cross-section of the flue is already seriously
oversized. For that kiln 9"x9" should be plenty large enough inside the
flue.
Your kiln is a little tall for it's width, which can easily contribute
to vertical temperature differences.
I'd be tempted to fire the kiln with a few firebrick and witness cones
in it before I'd start raising the stack height.
I hope this helps.
Dave Finkelnburg
-----Original Message-----
From: GREG MARSHALL
To: CLAYART@LSV.CERAMICS.ORG
Date: Monday, October 02, 2000 6:42 AM
Subject: Chimney height
I recently was hired as the pottery instructor at a small college. When I
looked at the kilns, the first thing that struck me was that the chimneys on
the two gas kilns were the shortest ones I had ever seen. I contacted the
previous instructor and asked her how the kilns fired. She said that they
were uneven with the top being several cones ahead of the bottom. My first
thought was that the draw was inadequate due to the short chimneys.
I've figured how tall the chimney should be on the larger kiln based on
information in Olsen's "Kiln Book". I would like some feedback to make sure
I am figuring correctly and to make sure I'm not overlooking something.
The kiln is a sprung arch with hardbrick on the outside and softbrick on the
inside. It fires on natural gas with four atmospheric burners.
The dimensions of the inside of the kiln are: 60 1/2" tall from the floor
to the top of the arch, 45 1/2" wide from wall to wall, and 50 1/4" long
from front to back. The four burner ports each measure 4 3/4" x 4 3/4".
The flue opening is seperated by supporting bricks that makes two openings
that are 5 1/2" x 8". The inside of the chimney measures 12" x 20 1/2" and
the chimney is 8'10" tall from the inside floor to the top of the chimney.
Based on Olsen's formula that 3 x dp(downward pull) + (hp(horizontal pull)
divided by 3) = height of chimney I come up with a chimney height of 17.05'.
I live at 6000' so according to Olsen the chimney height should be increased
by 30%.
Any help or feedback would be greatly appreciated. Thanks.
Greg at the foot of Pikes Peak
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
John Weber on tue 3 oct 00
I have a propane gas downdraft car kiln with roughly the same size interior
as yours. My input is by 6 natural draft burners vertically mounted through
4" holes. My exit flue is 9" by 9" with a 1" divider. The Chimney is 10"
across steel pipe, with total height of 10Ft. The kiln fires within a half
of cone up and down. I have worked on the sizing a lot, it originally was
not getting to temperature and stalling at the high end. When I opened up the
exit flue it fired fine. Yours seem to have too much opening in the chimney
for me. I think it works better for me if the exit size is a little larger
than the entrance size. For what its worth. Good luck.
John Weber
ferenc jakab on tue 3 oct 00
Based on Olsen's formula that 3 x dp(downward pull) + (hp(horizontal pull)
divided by 3) = height of chimney I come up with a chimney height of 17.05'.
I live at 6000' so according to Olsen the chimney height should be increased
by 30%.
Any help or feedback would be greatly appreciated.
Graham,
Olsen's figures are based on early ideas derived form experience with wood
fired kilns. Gas kilns do not need as much chimney. As a rough rule of thumb
decrease Olsen's height calculations to about a third. His flue opening size
calculations are pretty well correct. Do the kilns vent into a canopy where
the hot flue gasses mix with fresh air before final venting? This helps to
draw the chimney if the canopy is correctly sized (10-20%) larger than the
kiln flue.
All in all, I believe the problems are with firing technique or kiln
design, rather than chimney size. Incidentally, do the chimneys have
baffles? Baffles are essential to good kiln control.
Feri.
ARTISTINSC@AOL.COM on tue 3 oct 00
My 2 burners are blower and are rated 750,000- 1,000,000BTU and does not
need the tall chimney but I understand the atmospheric burners will need more
draw. I use target bricks, no bag walls.
Margaret
GREG MARSHALL on wed 4 oct 00
Thanks to all of you who responded to my query about the chimney height. =
You made me realize that I need to slow down, think about other =
solutions, and mainly, fire the kiln myself and see what happens.
In fact, since my post, additional information has become available. I =
asked a person in the studio who had assisted the previous instructor =
how they controlled reduction in the kiln and he told me they never =
adjusted the damper, just adjusted the burners. I've always used the =
damper to control reduction and the kilns I've used in the past would =
definetly have fired hotter on top if the damper had been left open.
So, I'm just going to load it up and fire the way I know how to fire and =
see what happens. I'll let you know.
Thanks again.
Greg at the foot of Pikes Peak
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