John Weber on sun 24 nov 96
I am rebuilding my Minn. Flatop 36 cu ft gas downdraft kiln, using 6 natural
draft venturi burners mounted from below the floor of the kiln, 3 burners
in-line on each side. This design is similar the the Geil design. My
question is how tall to construct the stack. I appears to me that Geil
advertises their kilns as not requiring a stack much higher than the kiln
itself, while most other kilns seem to use about 15 to 18 feet of stack. If
anyone has any suggestions I would appreciate hearing them. Thanks
Jonathan Blitz on mon 25 nov 96
I built an MFT according to the plans given by Nils in his book.
I used a 16 foot section of 12" I.D. galvanized culvert. It has worked
very well, and was about $90.00 from a farm supply store.
I would caution you to guy wire it VERY securely, and have three or four
strong individuals, one sitting on the top of the kiln wall and holding
onto the center of the stack, while erecting it.
Jon!
William Brouillard on sun 19 apr 98
kiln stacks, a irrelevant observation
Years ago I was helping with the construction of a kiln. Since it was going to b
It also changed the draft of the kiln. Kiln draft, As I understand it, is depend
The insulated stack kept the bottom of the stack hotter than before and the draw
--
william brouillard
1011 literary road
cleveland,oh.44113
ch151@cleveland.freenet.edu
William Brouillard on thu 23 apr 98
This is a repetition of an earlier post. I seem to be having trouble
with my spacing. I am looking for the fix but will send this
off as is.
kiln stacks, a irrelevant observation
Years ago I was helping with the construction of a kiln.
Since it was going to be a student fired kiln and all of the
burners were located in the back of the kiln, I suggested
that we use some soft brick to insulate the bottom of the
stack. The idea was to make the outside surface of the
hard brick stack cooler at the base to avoid accidental
burns in the cramped quarters around the kiln controls. I
used some salvaged K-23s from the previous construction
and added 4.5 inches of insulation to bottom of the stack .
I insulated to a height of about three feet or just past the
damper and burners. It kept that area cooler and reduced
the risk of burns.
It also changed the draft of the kiln. Kiln draft, As I
understand it, is dependent on the temperature difference
between the top and bottom of the stack. The greater that
difference, the greater the draft. The volume of the flue
and stack must be adequate to the size and type of the kiln
and the interior surface of the stack can affect the amount
of drag or loss of velocity of the gasses moving though it.
The insulated stack kept the bottom of the stack hotter
than before and the draw was greater. The better draw
allowed us to use a shorter stack and perhaps we could
have used a smaller flue.
--
william brouillard
1011 literary road
cleveland,oh.44113
ch151@cleveland.freenet.edu
Mary Dye on fri 24 apr 98
I just finished reading the post by Wm. Brouillard re: the temp. difference
from top to bottom in a stack, and how that can increase the draw, allowing
a shorter stack to work as well as a taller one. I've got a question -- my
stack is about three feet shorter than it should be, but it works great
anyway (kiln is 40 cu. ft.). However, I've got just the opposite situation
w/ the temp. variation from the one described -- my stack has a hard brick
base and hard brick for about the first two feet -- and then the rest is
IFB. It is built this way because I ran out of hard brick and decided to
use left-over odds and ends of soft brick to complete the stack. Anyway --
the temp. of the stack itself during firing is much hotter at the bottom
than the top. It works fine -- is the temperature variation part of the
reason I'm getting a good draw?
Mary
Cameron Harman on fri 24 apr 98
To William Brouillard in response to your post.
The stack draws based on the difference in temperature between
the outside air and the temperature of the gas just leaving the
stack. As you insulated the base of the stack you allowed the
temperature of all the gasses in the stack to get hotter, so the
exit temperature was higher and the stack would draw better.
Looks good to me all around. It is always better to avoid those
hot places around a kiln that could cause a burn.
Good job.
Cameron Harman
--
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