Kiln Leaking A Lot Of Heat - Likely From Lid

[clayshapes]

I bought an old kiln (cone art) to use at my summer cottage, and retrofitted it with new elements and a new electronic controller. The interior bricks are in excellent condition, but the lid has several small cracks. After firing it a couple times (bisque and cone 6) I see that it is losing a lot of heat, likely through the lid. I leave a window open during firing - but the room is super hot - so hot that I'm afraid it's actually a fire hazard. I can see a glow between the lid and top of the kiln when it's reached temp. (pieces in the kiln fire well, generally - although during the last glaze firing two flat platters on the top shelf cracked - so I'm assuming it's cooling too quickly. Only the top shelf has this cracking problem).

 

I've read a lot of stuff about this - some people use fire blankets (sounds scary). I was thinking of putting an old kiln shelf on top while firing, to try to keep the heat from escaping. This might be a dumb idea because of the weight on an already fragile lid. Am thinking of getting a new lid. Would love to hear some advice here.

[Pugaboo]

To test the issue next time you fire, place a kiln shelf on posts directly up under the lid. Basically fill your Kiln then put posts and another kiln shelf so that it sits at a height just under the top of the kiln. This should help keep the items on your top shelf from cracking from cooling too fast as well.

 

If the lid is lifting up from the heat as it fires you can also put a metal clasp lock on it and use it to hold the lid down. That's what the kiln at the art center has on it. If you want a picture of it let me know and next time I am up there I will take a picture of it.

 

I have been told that using a fire blanket on a kiln can damage the metal jacket because of the trapped heat between the brick and the fire blanket. Not sure if this is so, so I'm hoping the kiln gurus here will chime in.

 

T

[Marcia Selsor]

you could buy a piece of ceramic fiber on eBay. Some people use that. It is not the greatest solution as firer i hazardous. Make sure to find a piece made of the "safe"fiber.-the type that breakdown in your lungs. Pugaboo's suggestion is a good one. I do that when I want a slower cooler.

 

Marcia

[neilestrick]

The lid will lift during the firing. That's totally normal. The hot face of the bricks expands and the lid bends, creating the lift and gap. A new lid will not help the situation. If it's hitting temperature within a reasonable amount of time then it's fine. Put a kiln shelf at the top of the stack to act as a secondary lid if you want to slow down the cooling. I wouldn't put platters on the top shelf, because you end up with a short shelf up there that will likely run cold. You can try putting a clasp on the lid, but that may cause damage to the lid since it own't be able to move as it expands with heat. New kilns that come with clasps have hinges that allow for movement.

 

Kilns put out a lot of heat. Depending on the size of the kiln, it will heat up a room a lot. Do not try to wrap anything around the kiln. It's unnecessary and will just damage the metal jacket. If the room is getting too hot, you need better ventilation.

[Dick White]

A couple of thoughts -

 

1) Place an electric fan in the open window of the room. Just having the window open is not going to create airflow to take the heat out. You will also need some other source  (door ajar or another window or vent) of fresh cooler air to be drawn into the room from the other side to replace the hot air the fan is blowing out.

 

2) Check the placement of the hinge on the back of the lid. There should be some vertical play in it when closed. The heat from the kiln will cause the bottom face of the lid to expand more than the cooler top face, resulting in it bowing a bit. If the hinge in the back is tight enough that the lid can't flex a bit, the front edge will lift up when the kiln is at red heat. Pugaboo's suggestion of a clamp will also keep the lid shut, but be sure you get a heavy duty stainless steel one, one from the corner hardware store (are there any of those left?) won't hold up for long. (Or peruse the repair parts catalogs of other kiln manufacturers to find a suitable item.)

 

3) If you do choose to buy a new lid, get a 3" thick lid even if the kiln sides are old-style  2.5" brick. It will provide more insulation value at the location where the passive heat loss is the greatest. Then place the old lid underneath the kiln, creating an effective 5" bottom, for extra insulation at the location of the second most heat loss.

[clayshapes]

Thanks for all this great advice. I was just so shocked at how hot it is in the room, compared to my kiln in my studio in the city, which NEVER heats up the room like this. This is a bigger kiln though.

 

The kiln is reaching temp at the expected time - but it's cooling more quickly than my kiln in the city - hence one of the reasons I think it's loosing more heat than it should.

 

I did put an empty shelf on stilts, as Pugaboo suggests above, just above the top shelf, and had no issues in the following firing. I also avoided putting flat pieces on the shelf just below...worried they would crack. It's always so tempting to fill one more shelf when there's just a bit of space left, and glazed platters are ready to load!

 

I'm going to check the back hinge as Dick White suggests...and for the next firing, I'll take all the good advice here from Dick and Neil Estrick about better ventilation - I'll leave a window open, at one end of the room, and the screened sliding door open near the kiln, - with a fan pointed out the window to move air out - and hope for the best.

 

Will keep my phone handy to call 911 if I see any flames! (just kidding - don't think this is a real issue).

 

Thanks again for all the advice! It's great to be able to come here with an urgent question and get such immediate results!

[CarlCravens]

I tried a fiber blanket on top of my old Paragon once... it caused the paint to melt.

[neilestrick]

I tried a fiber blanket on top of my old Paragon once... it caused the paint to melt.

 

Paint? Why was there paint on your kiln?

[CarlCravens]

Paint? Why was there paint on your kiln?

 

The silver/grey coating on the top of the lid.  Apparently this was a thing in 1967 for Paragon.