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bottom heat kiln.

Posted: Mon Mar 16, 2020 6:02 am
by Michael Stevens
I ordred a kiln that has a heating element on the sides and the bottom. I assume I need a thick shelve on kiln posts above it so shelf won't crack and airflow

anyone have experience with bottom heat

Re: bottom heat kiln.

Posted: Mon Mar 16, 2020 8:13 am
by Brad Walker
What does the manufacturer recommend?

Re: bottom heat kiln.

Posted: Wed Jul 22, 2020 11:33 am
by Sharol
Hi.

I’m considering a new kiln with top and floor elements and saw this post. I’m curious if anyone here sees a disadvantage to this arrangement. I’ve seen where some European manufacturers offer this as an option in their glass kilns. The kiln I’m considering has a 27” x27” x 17” (depth) chamber. Clamshell design. All rigid fIber sides and top and a brick floor.

Your input would be very much appreciated!

Thanks!
Sharol

Re: bottom heat kiln.

Posted: Thu Jul 23, 2020 8:59 am
by DonMcClennen
I've been firing glass (large and small) going on 30yrs. Always with top elements and a few side ones.. I can think of numerous reasons to not want bottom elements. I suggest you reconsider!

Re: bottom heat kiln.

Posted: Thu Jul 23, 2020 9:13 am
by Brad Walker
Bottom elements have been used in pottery kilns because a clay piece (especially a flat piece) on a shelf at the bottom of the kiln may not get enough heat to fully fire. (Top of kiln hotter than bottom of kiln) The bottom element helps even out the heat. This is especially useful in pottery firings where multiple shelves are used. Multiple shelves, which are common in pottery, can also contribute to lower temperatures at the bottom of the kiln.

In a glass environment we don't have the same kinds of worries as the potters do. Elements in the bottom of the kiln would be useful for casting large pieces, but I'm not sure they're useful for firing glass on a single shelf.

Does the kiln you're looking at allow you to turn off the bottom elements if not needed? Many of these kinds of kilns do. The big risk with bottom elements is crap (technical term) falling onto the floor elements and potentially damaging them.

Re: bottom heat kiln.

Posted: Thu Jul 23, 2020 9:42 am
by Michael Stevens
well overall this little pottery kiln has done quite well. when slumping it really helps. overall I've had very few bubble problems that I got with top heat.

if I fuse 2 or 3 shelf layers the bottom is hotter so I put things that need hotter temp at bottom.

I do put 3 inch stands to raise bottom shelf.
I do sometime need to crack the lid to keep temp raise slower before 500c if close lid even with a slow ramp. can crack large sheets.

a glass kiln would be ideal but at 4 times the cost I'm. pleased with what I have

Re: bottom heat kiln.

Posted: Thu Jul 23, 2020 10:19 am
by Sharol
Thank you all for your replies.

Brad, the “crap” issue has been one of my primary concerns with this configuration. No, the proposed bottom elements can not be controlled separately from the top elements.

I will not be doing any deep casting and never fire multiple shelves, so I’m going to pass on the bottom element configuration.

I posted a few months ago about my search for a replacement kiln and received great Input from Board members. I don't have the wherewithal to build a kiln myself and so I am discussing a quasi-custom build with a manufacturer I have had good luck with in the past. It was his initial recommendation to install the floor elements.

As things stand now, it is:

1. Clamshell, single opening design
2. Sides and top hard fiber board
3. Floor brick
4. Interior chamber 27 x 27” x 18” height (To accommodate 24” square shelf)
5. Quartz encased top elements
6. 45 amp, single phase wiring (NEMA 6-50 receptacle & plug). I have 200 amp service to my shop and so could handle more juice, but was avoid to avoid hardwiring or going to 3 phase.
7. Solid state relays

I’d appreciate your opinions andwisdom on this.

Thank you!
Sharol

Re: bottom heat kiln.

Posted: Thu Jul 23, 2020 11:39 am
by jim simmons
As long as you are having it built, why don't you have a switch installed so you can turn the bottom elements off?
The other Jim

Re: bottom heat kiln.

Posted: Fri Jul 24, 2020 10:25 am
by DonMcClennen
someone once made a wise statement: Glass needs to "see" the heat.. while pottery only needs to "feel" it! That is why elements in glass kiln roof and no multiple shelf layers when firing :) . Don

Re: bottom heat kiln.

Posted: Sun Jul 26, 2020 10:32 pm
by Buttercup
Hi Sharol,

I'm curious about the 'Hard Fibre Board' you mention, having a bad experience with a fibre kiln: see my post in your earlier thread: viewtopic.php?f=2&t=43134&p=362735#p362735
Do you have a link to the material, please. It would certainly cut down on weight and space compared to a brick kiln.

Re: bottom heat kiln.

Posted: Sun Jul 26, 2020 10:50 pm
by Sharol
Hi Jen. I’m sorry, but I don’t have a specific spec sheet or manufacturer link for the hard fiber board. I believe it is the same material as is fairly common in kiln lids and also in Jen-Kens all fiber kilns.

Re: bottom heat kiln.

Posted: Sun Jul 26, 2020 11:18 pm
by Buttercup
Thanks, Sharol.

I've heard of, but don't know anything about Jen-Ken kilns but I can check their website.

I'm sure the technology has improved since the disaster I described before. Good luck with the new kiln.