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achieving uniform heat-perf./stagger'd shelves (& ken's hybrid

updated thu 15 jul 04


Ken Nowicki on wed 14 jul 04

kiln project)

Hi Bill... sorry this reply is so late....

This idea about using perforated kiln shelving is still new to me, but, from
what I understand they use shelves like this in industry in huge kilns very
successfully. I may be entirely wrong here, and perhaps someone else that knows
more about it could shed some light on this topic but... I was under the
impression that the holes themselves aren't that large (maybe 3/8" to 1/2" inch)
and evenly spaced throughout the shelf... and that it didn't require any loss of
space... that the wares would be placed on the kiln shelf in the usual
fashion. I could be mistaken here, but I thought part of what the whole idea about
using these perforated shelves for in the first place was that it evens out the
temperature of the kiln throughout more efficiently and let's the kiln
"breathe" better overall. I'm guessing that there are no real significant problems
(warping, unusual shrinkage, etc.) by placing the wares on the shelving without
too much regards for where the holes are in the shelf. It seems to me that if
the flame path/heat is allowed to move less restricted, that the kiln will
fire more evenly throughout and the hot and colds spots that cause some of the
problems mentioned above would be minimized... not exacerbated. Thoughts...
experience... anyone?

As far as using half shelves staggered or butted together... I don't think it
is necessary to require a full or half shelves butted together at the top to
"cap everything" and "help hold and even out the heat, top to bottom"... just
doesn't seem necessary to me. Just my 2 cents anyway.

I do think however that having a solid full round shelf at the bottom for an
electric/gas hybrid that has it's burner port at the center bottom of the kiln
is probably a good idea however... and the reason being that I believe that
the initial flame path coming out of the burner might spread more evenly to the
edges around this first shelf before it continues up into the remainder of
the kiln. Since this is the first initial blast of heat from the gas burner, it
might be prudent to shy away from any wares being in the direct path of the
initial flame that is so close to the burner. Although, it may warrant
experimenting with two half shelves at the bottom (either butted up together, or split
slightly apart) just to see what would happen. It'd be interesting to see the

In the hybrid gas/electric kiln that I am building this summer, there will be
some changes in design as compared to what has traditionally been done before
with these hybrids. At least, as far as I know... this kiln I'm building with
L&L will be the first of it's kind... for several reasons. One of which, and
perhaps most drastic is the change from an updraft... to a downdraft (or
somewhere there in-between). This may prove to be a challenge to obtain the desired
reduction atmospheres I'm looking for... but... with careful adjustments,
record keeping, and lots of initial testing... Mel & I are pretty confident that
it will work fine. [BTW, "our mayor", Mel, has been standing on the sidelines,
coaching me along on this kiln project all along... offering encouragement
and giving me the confidence to tackle this. I am indebted to this man. Thank
you Mel.] Rather than placing a burner at the bottom of the kiln and letting the
flue gasses escape through a 1.5" or 2" inch diameter hole in the center of
the top lid of the kiln... I will be incorporating the use of L&L's "VentSure"
downdraft kiln ventilation system... only... not through the bottom of the
kiln as it is normally done... for this area is reserved for the burner port...
but the VentSure will be placed at the bottom SIDE of the kiln instead. The
amount of draw will have to be carefully adjusted during the reduction phase by
adjusting the vacuum bypass control on the side of the bypass/collection box
so as not to draw out too much air at once... eliminating the reduction
atmosphere that's desired... yet... allowing enough air to be drawn out to ventilate
the kiln as needed. This will be somewhat of a delicate balance, and a lot of
testing will have to be done. As mentioned in my previous post about
oxyprobes... due to the possibly challenging task that awaits me... this is why I feel
investing in an oxyprobe will be critical for me to get a handle on what's
going on inside this kiln while I make these adjustments with the vacuum bypass
slide valve. This is all unchartered territory, but I am willing to take the
risk... and confident that it will work.

If you're wondering why I would make such a change in ventilation design it
is because these kilns are typically fired outdoors or outside under a
protective shelter of some sort. In my situation, that is not currently possible, so I
am putting this kiln into an enclosed section of my basement... the area
referred to here on the East Coast as a "boiler room". In fact, there is no
"boiler" present, however at one time in this 1890s Victorian I'm sure there was...
but now this room shares the space with a modern furnace/FAU unit, a water
heater, and the electrical panel (see my previous post on "Safety Issue" Make-up
Air"). Due to the safety issues of firing in an enclosed space, I wanted to
have this kiln's gasses vented directly outside, for obvious reasons... hence...
the VentSure system. In addition, relating to safety issues... I opted to
replace the traditional fuel design of using a Bunsen burner attached to a
propane tank... to using a small venturi burner using natural gas. There will be
various safety measures put into place in this burner design. I simply was not
comfortable with using propane in this situation, not with the way the gas sinks
to the floor and especially being in such close proximity to a gas burning
water heater nearby. Plus, I already had natural gas nearby.

It's all exciting stuff... and I'm eager to get things going on this.
Hopefully, things will go well in the firings once it is installed, and I'll have
much more to report back to you all then. I plan on documenting the construction
of the kiln for a possible article for publication later on... we'll see how
it goes. :-)

Best wishes,

- Ken

"where I'm getting excited as things slowly start to come together on this
project... just had my plumber out yesterday who installed the gas line for this
kiln, but even more importantly... he put in a new "library"... er... uh... I
mean... toilet!!!... for my new basement studio! Whooo Hooo!!! Now all
I need is to install a real nice magazine rack nearby to hold all my Ceramics
Monthly, PMI, & Clay Times magazines!!!"

Kenneth J. Nowicki
Port Washington, NY
Charter Member/Potters Council

In a message dated 06/23/04, wschran@COX.NET writes:
Ken wrote:>.....was interested in perforating my shelves with small
drilled holes to perhaps assist the kiln in achieving a more even firing.....
But, for
now... I've decided to use mostly "half shelves" and stagger them... using
only one full round shelf on the bottom. I think staggering them throughout the