mel jacobson on tue 4 sep 07
i know that many out there in clay land have a
very old concept about flue size. many read
nils lou's book, use his plans....then make a
60 square inch or 81 square inch flue.
if you are going to follow his plan for a kiln....take
note of his double venturi flue. it is the heart and
soul of the kiln. don't rewrite his plans then bitch
about the kiln not working.
i have had to rebuild several kilns lately. (nice pay day.) all kilns
built on nils' plan. one added a bag wall, and then
built a very loose chimney with a single flue of over 70 inches.
it would not fire to cone 3.
i wonder why? the passive damper was the entire chimney.
it would have worked with a kiln shelf covering the entire
chimney. i do not understand folks that hire me to re/build
a kiln back to the original plan...then argue with me about
the flue size...follow the plan.
there are many that just don't believe a kiln will function
with a 36 square inch flue opening. sorry to tell you...it
does work. mine is now 35 years old. 45 cubic feet, double
venturi system....and a spiral pipe kaowool lined stack...13 feet high.
i use natural gas/45 year old denver fire clay burners..house gas
run 50 feet to the kiln...underground...inch and half steel pipe.
i am sure i have less than one inch of water column. i fired about
30 times to cone 13 for the iron saga project. i know it would
fire to cone 16. all i do is turn down the gas. yes, turn down
the gas. it fires hottest at half on/off.
kurt, bob anderson, dawn, bob fritz and me...and a dozen others i know
have build the tiny kiln...16 cubic feet...with all the same specs.
they fire perfectly....including our farm kiln that will make cone
11 in four and half hours....propane 12 pounds of pressure. welding
hose from the 3/8th inch copper underground copper. ( we hold that
kiln back and fire in about 6 hours. our big salt kiln has the same flue.
it fires in about 6-7 hours...cone 10 just over.
not one minnesota flat top has failed in my experience. no
explosions, no failures,
even with compressed air burners. i have seen some sagging roofs,
but of course,
the kiln was never tightened /retuned.
if i was building a compressed air burner system into a large kiln (60 to 100),
i may go 45 square inches for the flue...add a bit of insurance.
but, i doubt that it is necessary.
i know that nils has read about and seen many industrial kilns over
the last few years.
he was trained by j.t. abernathy and was convinced that most
kilns allowed heat out the chimney....terrible designs, with huge flue systems.
total waste of fuel.
industry does not waste fuel. they engineer their
kilns to be efficient and clean. it does not pay to have a bad kiln...esp
if your fuel bill is one million dollars per year. they fuss.
i know that edourd's dear friend in france...smart coucil does not
make dumb mistakes with his glazes... millions of items fired to perfection.
all engineered to fire with efficiency and economy . why is it that
potters often think that industry is our enemy? why did david finklenberg go
to alfred? get a ph.d.? to make dumb mistakes? he is one of our
most valued of clayart experts.
clayart is wealthy with some great technical minds. they try to
educate potters in being better and better. i hope folks are paying
attention and appreciate what they give us..
a well engineered kiln will fire any way you want. you can fire for
serendipity, or production. you can fire any temperature, you can
fire for uneven reduction, but, if you have a bad kiln...it will never
fire a load at 100 percent perfection. so, you don't want quality?
build a bad kiln.
i have always said...if you want to be an ecologist, save the world,
never throw away a soda can....why waste gobs of fuel, fire a bad
kiln and heat the air? fire for perfection, fuel saving, heat saving,
and the best fire you can make to make the pots you want.
nils has given us a great book, full of valued information.
why re/write it with old technology that has never worked.
just like making safe glazes, using safe materials in a clean studio....
make sure your kilns are running at peak performance.
mel
from: mel/minnetonka.mn.usa
website: http://www.visi.com/~melpots/
Clayart page link: http://www.visi.com/~melpots/clayart.html
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