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I am looking to get a larger kiln. The units I am looking at are top loading ~13" depth. (e.g Evenheat 2541, Skutt GM 1414, Olympic 3014GFE). Elements are contained in the lid, and sides.

I would like to add a 2nd shelf in order to fire on 2 levels at times.

From reading this forum, it seems this should be doable (with some practice).

Anyone see any issues with this?

I have tried it several times with limited success. Seems that the distribution of heat is not even throughout the kiln. Had a wide disparity of results in one firing.
Stacked 2 shelves 3 inches apart. Lower shelf had much higher temperature than upper shelf. Note this was in our larger side firing kiln. I did not use the upper elements because I assumed radiant heat from the top elements would have made the upper level much hotter than the lower.


Barry

I'm with Barry. You can certainly do it (I have), but it's mostly a pain in the neck.

I wind up figuring out how to position pieces so that the ones that need the least heat are on the super-insulated bottom center shelf while the exposed upper edges contain the work that needs the hottest firing. Since it's not likely that the mix of pieces I want to fire will fit those requirements, I generally wait until they do. I could probably squeeze two firings in the waiting time, so I haven't really saved anything. Or I go ahead and fire with empty shelfspace, which kinda defeats the purpose.

You can get around that to some extent by slowing the firing way down, spending more time at each segment, and going a bit hotter at the top temp than you normally would. The heat evens out and you get a more uniform firing. You also have to contend with overfiring the glass and a higher risk of devit. And again, the firings are longer with more chance that you'll have to remake and refire failed pieces, so I'm not sure if double-stack firing really saves much time with normal fusing projects.

All that said, I *do* fire on multiple levels occasionally, mostly for firing what I call "kiln murrini," i.e., pattern bars with tiny repeating patterns that will be sliced up into cane. Those are fired inside ceramic boxes called "saggars," which already superinsulate the glass so a little more doesn't really matter. The firings fit the above requirements, i.e., hugely long bubble squeezes to remove bubbles, 4 hours or more at higher-than-normal process temps, and I could care less about devit because I'll be cutting and grinding them anyway. (for more on that: http://www.morganica.com/bloggery/2011/ ... es-part-i/ )

I fire on the floor of my GM1414 and have a shelf at mid-level. The bottom shelf seems pretty consistently 200 degrees cooler than whatever is on the top shelf. So, when I fire 90 or 96 glass, the bottom shelf is for flattening bottles, warping sheet glass, etc.

One of my large kilns is a skutt gm 1227. In it I load up 5 or 6 layers in a firing. It is only side fired and is an incredible kiln for production. That being said I pick and choose what I fire in it because I have 6 kilns all with different abilities and strengths. When I layer in my tall skutt I make sure I leave "breathing room" although I have never used baffles like others have mentioned here in the past. I also used slightly adjusted schedules.
If I only had one kiln I would feel differently.....but I love my skutt for production work.
With a kiln the size as the one you are talking about....13" tall I would probably give it a try and choose work that will fire properly but I would always suggest getting the largest kiln you can afford and fit in your space. I also have 2 skutt gm1018s which i fire with at least 3 layers........

Patty Gray does this all the time when she teaches a class.
Jim

Im new to glass fusing, But I just ordered a new kiln last week. I went through a lot of the questions you are asking. I also have a little inside help. My brother is an HVAC tech and he is the go to guy with all heating and cooling questions. And a kiln is basically one big controlled heating element. So we talked and I brought up multiple shelves. he said what everyone else seems to be saying. He said heat moves differently and rises. The top will be drastically different then the bottom. When a shelf retains that heat it will help the air on that level stay whatever temp it has reached. In theory its possible to have a large kiln be up to 300 degrees different. He did all these crazy math equations, I just looked up online and read that it seems possible if you do it right. Thats just for my research, I have no actual experience with multiple levels yet. I do plan on experimenting when my kiln arrives in a few weeks. I will be keeping track of my firing schedules and I will gladly share notes.

I do wanna bring up something I learned about oval kilns. Now I cant get one because of space issues. But I learned heat travels better in a circular space. It takes more time, energy, and heat to fuse glass in a large oval then it does in a circular kiln or even a square kiln. Now that time energy and heat may not be noticeable when firing on one shelf. A circular kiln and and oval kiln can both use the same firing schedule and you wouldn't notice the difference at all. But the difference will show up when firing on multiple levels.You would probably see a huge difference between the bottle shelf and the top. Theoretically almost 400 degrees. But every kiln is different. Its definitely possible it seems it needs a lot of practice. I wouldnt have even thought about something like that. But my brother has to think about things like that for a living he brought it up. Id still buy an oval kiln if i had the room though.... lol Again i have no actual experience in multiple shelves yet but I just asked myself these questions and spent some a lot of researching the answers.

So i learned its not impossible, but with anything it will require practice.

if you buy a kiln with an envirovent and multiple zone controll. (scutt has this) the kiln is darn near equal from top to bottom. i can use 4 shelves in my scutt and if i place them at the proper heights, get the same amount of heat work done on all 4 shelves. r.

Oh, absolutely, Rosanna. In fact, you don't need the zone control at all, just the envirovent. Or you can get some quartz tubing, some flexible tubing and a tiny airpump, drill intake and outflow holes in the kiln, and get much the same effect as zoning. The slow movement of air from top to bottom tends to even things out--I use that when I'm doing really thick casts--but it does slow things down a bit. I would think it would work much the same way for multiple shelves.