[yedrow]

Is there really a big difference? I've only used a downdraft kiln (not counting electric). I have an old DLS electric kiln that's around 20 cubic feet, (the elements were about 3/4 in. dia.) and I want to convert it to a gas kiln. However, it has a vent in the top that is something like 8" sq. A colleague said I should make it an updraft kiln, but everything I've read says that downdrafts are more easy to control.

Any opinions?

Joel.

[LilyT]

yedrow, on 15 August 2012 - 10:39 PM, said:

Is there really a big difference? I've only used a downdraft kiln (not counting electric). I have an old DLS electric kiln that's around 20 cubic feet, (the elements were about 3/4 in. dia.) and I want to convert it to a gas kiln. However, it has a vent in the top that is something like 8" sq. A colleague said I should make it an updraft kiln, but everything I've read says that downdrafts are more easy to control.

Any opinions?

Joel.

Were you thinking of doing a very complicated setup?
Since it already has a hole on top... would it be hard
to set it up as an updraft first and fire it that way... and
then change it to a downdraft and compare the two
styles.

And then report back to the forum :-).

From what I've been reading about industrial kilns, it
seems that turbulence contributes majorly to even-ness
of the firings. If you could set up your burners to be
be very turbulent (like pulse burners) it's supposed to
be exceptionally fuel efficient and provide excellent
spacial uniformity. Irrespective of updraft or downdraft.

(I wish I had the resources to play with pulse burners)

-Lily

[Mark C.]

Joel
This is one area I have lots to say about as I own and use both styles.The updraft was used for 400$ so I picked it up cheap.
The updraft (12 cubic feet) is always a few cones hotter on bottom (6 or 4 bottom burners to choose from)no matter what is done. the top is always cooler-always no matter how its stacked or fired.
I have leaned to load it with the right glazes in the right spots-Its a pain but its manageable.
You are always trying to even it out-I load the flue tighter to slow the heat loss down now with better results.

My downdraft is almost even to fire day in day out- never adjusting it to even out as its always even-only lower back shelve next to flue is cool-so a cool glazes go there.
The heat/reduction is better used in a downdraft-better circulation and better results constantly.
My salt kiln is also a downdraft about 24-26 cubic feet-fires very well and pretty even until we salt it then the top gets hotter.
Seal that hole up and cut one in the side wall at bottom and hook up a stack never look back.

you said(I've read says that downdrafts are more easy to control.)
this is more than a true statement-20 cubic feet should be large enough to work well as a downdraft. The bag wall is the thing that needs to be the right size.
Mark

[Marcia Selsor]

I learned to design , build and fire downdrafts in college although we did have one very old updraft that was so old the floor level had changed requiring a ladder to load it.
I fired Alpine updrafts in grad school along with a huge downdraft salt kiln plus some kilns we grads built. I built all down drafts for the college program in Montana where I taught for 25 years. Then fired West Coast updrafts in Hawaii where their kiln room has at least 10 big kilns of various sizes. This program had 150 students and we fired big kilns often.This past year I fired a 20 year old Olsen updraft about 60 cu ft. With rusted burner controls and major cracks. I always preferred downdrafts but this old Olsen kiln and the West Coast Kilns fired very well. The previous instructor left great kiln logs for an easy firing.the Olsen. I fired my downdraft kilns sometimes four times per week. I had the schedule down pat.
In all, it just depends on the design and you familiarity with the kiln to get it to do what you want.

Marcia

[yedrow]

This kiln will be my first attempt at doing anything like making my own kiln. That being said, it is pretty much already made. To make it a downdraft I would have to cut through the back; meaning through hard brick and a sheet of steal. The top has a damper though. I'll try to get some pics this weekend, this thing is a monster, weighing in at about 5000 pounds. Given Mark's and Marcia's comments a downdraft would be best. But it would be a lot of work and I would structurally alter the kiln in a major sense.

Joel.

[Mark C.]

JOEL
I CAN TALK STORY ABOUT THIS WITH YOU IF THAT HELPS ON THE PHONE, MY number out west is 707-668-5983 I'm sure I can come up with some ideas that will help.
I will be tuna fishing all day tomorrow 5 am to 10 pm but I'll be here Saturday and sunday unless i run out agin for tuna-long boat trip 180 miles.
I'm off for bed
Mark

[Marcia Selsor]

someone somewhere made a down draft out of a cylindrical electric outcast kiln by inserting shelves vertically along one side to form a chimney on the interior. The shelves left the flu open at the bottom. I never saw this but the description was good enough to understand the thought process. There are many ways to approach it. talk it through with Mark. it is always a good idea to bounce ideas around with another potter. You might find the above kiln idea in the Clayart archives. it has been a while but it could be there.

Marcia

[yedrow]

Mark,

I'll do my best to get pics for you by Sunday. I'll be working until 10 tonight and probably midnight Saturday night. I should have some time Sunday to give you a call.

Marcia,

Thanks. The kiln is actual cubical. It is a very well made industrial machine I got from a mass production shop in Mississippi (long story that involved working outside during a tropical depression). It came as a 20 cu. fu. kiln, but I removed the 3/4" dia. elements and their ceramic trays and gained a bit more space. I really need to get over to my storage shed and get pics of this thing.

Joel.

[neilestrick]

Downdrafts tend to fire more evenly due to better circulation. But updrafts can fire evenly as well. They just take a little more practice to figure out how the kiln likes to fire. Either type can be made in any size and still work fine. Like someone else said, you could always start with an updraft and convert it later if you just can't get it to work. There's a lot of negative talk out there in the world concerning updraft kilns. Ignore it. I know a lot of people who are still using 30 year old Alpine updrafts without any problems.