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potterychick

Room Temperature during glaze firing

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Can anyone tell me why this is happening. I have a Vent Master down draft on the kiln - it just had parts replaced. The room temperature is creeping up to 100 degrees and have to run many fans, doors open to keep it at bay. Last week's firing got so hot in the room that the controller shut down and I had to do a re-fire. Could this be a problem with the lid? I have had this kiln for 6 years and have never had this problem before. Any insight is greatly appreciated.

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Mark C.    1,807

I few more details about where the kiln is? Was the outside temp 98 degrees? does the door open to outside air?

Mark

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The outside temperature was about 50 degrees. The windows and doors were all open with a cross breeze. I had 4 fans running - 1 ceiling fan and 3 floor fans - to create air movement. The kiln is towards the back of the room. However, I have fired this kiln at least 12 times per year for the past 6 years and this is the first that this has happened.

To keep the problem at bay, we hooked up a portable A/C unit. It was kind of crazy - the unit kept the air temp down as long as the doors and fans were also open and running. When we closed up the room and kept the A/C unit on, the temp was slowly and consistently creeping up. So we left all doors open, fans on and A/C running through the night. It kept the temp at around 85 degrees.

But why is this happening? I fear that the cost of running all these cooling devices will be prohibitive. In the past I have run the glaze firing in the summer with out this problem.

Any ideas of what has changed to cause such temperature differences in the room?

I'm trying to determine if it has something to do with the Vent Master or the Lid. Can't seem to figure it out.

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The outside temperature was about 50 degrees. The windows and doors were all open with a cross breeze. I had 4 fans running - 1 ceiling fan and 3 floor fans - to create air movement. The kiln is towards the back of the room. However, I have fired this kiln at least 12 times per year for the past 6 years and this is the first that this has happened.

To keep the problem at bay, we hooked up a portable A/C unit. It was kind of crazy - the unit kept the air temp down as long as the doors and fans were also open and running. When we closed up the room and kept the A/C unit on, the temp was slowly and consistently creeping up. So we left all doors open, fans on and A/C running through the night. It kept the temp at around 85 degrees.

But why is this happening? I fear that the cost of running all these cooling devices will be prohibitive. In the past I have run the glaze firing in the summer with out this problem.

Any ideas of what has changed to cause such temperature differences in the room?

I'm trying to determine if it has something to do with the Vent Master or the Lid. Can't seem to figure it out.

 

 

the ventmaster was never meant to remove heat from the kiln in any significant way--just fumes. Unless you're seeing gaping gaps in the lid, i doubt that is the culprit either. How big is this room that the kiln is in?

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The room is about 350 sq. ft with a 10 ft. ceiling. It's a good sized pole barn that was turned into a studio.

I can see a red glow through the crack of the lid when the kiln is running. One side of the kiln has a bit of a larger opening than the other, and that side of the room of the kiln is definitely hotter when it is running.

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Mark C.    1,807

My only Guess and its just a guess is you have some larger gaps in the kiln sections or lid. If its 5o degrees outside and in a small pole barn I could see it warming that space but a 100 degrees seems a lot with all that venting. When the kiln is up to full temps say over 1400 you should not see glowing red/orange anywhere without opening a spy plug. If you do have glowing gaps you will need to address them. Are the soft bricks all chipped up or is the lid falling apart?How flat are the the top ring of bricks??where they meet the lid?

Mark

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That's really helpful information. Thank you. When this firing is finally finished and unloaded I will do a thorough inspection of the tip bricks and the lid.

Do you know if the Skutt lid master has adjustments that allow it to be tightened? I will give a call to Skutt tech support tomorrow to see what they suggest.

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Marcia Selsor    1,301

The lids do rise up from heat expansion during the firings. The side farthest from the hinge gets the mort open. Nothing too serious if that is the problem. If the lip of the kiln has a lot of wear from leaning on it during loading, maybe there is a large enough gap to worry about.

My kiln shed has two heavy duty exhaust fans set to run at 110 F. In South Texas sometimes they go on when I am not firing.

The control panel is sensitive. Maybe you could have a small fan blow on it during the firing to keep it cool. I have done that when it gets really hot in my shed, if a kiln is cooling and another firing etc.

Any way you can turn the kiln to have the control panel to the most open part of the room? You might be able to patch the worn area with kiln cement or a braid of fiber. Fiber comes in rope form to use as a gasket.

 

Marcia

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The control panel is already facing the open room. I actually had the portable a/c blowing on the controller. I'm just baffled as to what has changed since the last glaze firing. I've run this kiln so many times w/o this problem. There must be something that has changed. I'll thoroughly examine the top of the kiln and the lid after I unload. Thank you for the input. I do have a few spots on the lip of the kiln that need some brick repair - that might be the problem.

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Can anyone tell me why this is happening. I have a Vent Master down draft on the kiln - it just had parts replaced. The room temperature is creeping up to 100 degrees and have to run many fans, doors open to keep it at bay. Last week's firing got so hot in the room that the controller shut down and I had to do a re-fire. Could this be a problem with the lid? I have had this kiln for 6 years and have never had this problem before. Any insight is greatly appreciated.

 

 

I know you are already using a fan to cool off the kiln's switch box. From your description, you are aiming it at the front of the box. It may help, though, to aim a fan into the louvers on the side of the switch box. The air should go into the louvers on one side of the box and out the louvers on the opposite side. Or you could aim the fan upward into the bottom louvers of the switch box. The fan doesn't have to be large. A fan with 4" blades is adequate. Just a gentle movement of air is sufficient. You also won't need an AC unit.

 

As I understand, the room temperature is 100 degrees F. Where are you measuring the temperature? How far away is the thermometer from the kiln?

 

Sincerely,

 

Arnold Howard

Paragon Industries, L.P., Mesquite, Texas USA

ahoward@paragonweb.com / www.paragonweb.com

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GEP    863

The thing that sticks out to me is that you just had some parts replaced on your vent. Then suddenly the problem appeared. I feel like this must have something to do with the changes made to the vent. If there is a problem with the structure of your kiln, it would have happened over time, rather than suddenly. I don't think a downdraft vent is supposed to remove heat from the room, but maybe in your case the vent was doing that before the repair. Was there a hole in the duct, or anywhere else in the negative pressure zone? Honestly I'm not sure if that explains anything, just wondering.

 

Although this scenario is different, at the studio where I teach, the kiln room gets very hot, even in the winter. We have three kilns (with downdraft vents) in a room about 250 sqft.

 

In my own studio where I had only one kiln* with an overhead vent hood, which does remove heat from the room, in the summer months the room gets uncomfortably hot, close to 90 degrees. This is in a basement that otherwise keeps itself at about 70 degrees when the kiln is not heating it up.

 

Mea

 

*until this past weekend when I got a second kiln ... woohoo!

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JBaymore    1,432

I'm with Mea's thought train on tracking this issue down. If the change is sudden.... look for thngs that have changed related to the kiln and the building since the time that it did not happen.

 

Local pickup kiln vents do not deal with the heat energy transfered to the room air from the exchange with the hot surface of the exterior of the kiln. They are designed to get oxygen into the chamner to complete reactions and to pick up noxious fumes and get them out of the kiln room.

 

While most electric kiln lids do have the issue discussed.... they trypically have this happen slowly over time. Not as a sudden thing. (BTW........ this issue can easily be fixed by routing out the pivot holes for the lid hinge to elongate them so that the back side lifts as the kiln expands.)

 

If you (or someone else) fixed the vent system....... is it possible that the fan is now running "the wrong way"? Meaning that rather than pulling fumes (and hot air) OUT of the kiln, it is now pumping fresh air INTO the kiln.... and hence causing the positive pressure created inside the kiln to cause the hot kiln gases to vent into the room thru the cracks in the kiln and the peep holes?

 

Or when the vent was "fixed".... maybe the connections to the output ducting (leading outdoors) after the fan is not tight.... or was forgotten to hook up again? Then the gases pulled from the kliln are getting partially or fully dumped into the room.

 

Have you chacked the outside termination of the vent duct? Did a bird or bees or rodent build a nest in there?

 

Or maybe did you add insulation to the room that the kiln is in since it was last fired?

 

Or maybe did you do some other weatherproofing to the room.... and cut down the naturla air turnover in the space?

 

Something drastic like this does not just "happen" naturally without a significant cause. Something is up.

 

best,

 

......................john

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hmmmmm.......lots to think about.

Here's more of the whole story - 2 weekend's ago I ran a glaze kiln. Packed tight! The room got to 130 degrees, the controller went into error mode. I cooled down the room to 80 degrees and did a restart. Checked on the kiln constantly until it was done. It ended up going to a perfect cone 7 instead of cone 6. Not such a terrible thing except that all of my cone 5/6 glazes got a bit runnier and darker than expected. SO the examination began.

We took apart the vent to clean it out and make sure that there weren't any bird nests in the hose. When we took it apart it became apparent that the hose was split and the cup under the kiln had not been lined up to the kiln holes properly. (I'll be more careful vacuuming under the kiln from now on.) So I thought this was the obvious reason that the room got so hot - the vent hose was dumping heat directly into the room.

SO we fixed the vent - new hose, new gaskets, lined it up to the best of our ability and purchased a free standing a/c unit.

Fast forward 1 week - loaded the kiln again, packed it loosely this time. Expecting it to be a perfect firing. ( I actually baked a birthday cake for the re-birth of the kiln and good karma) Right! Started the cone 6 glaze firing and kept a constant watch on it every hour. At about 1100 degrees the room started to creep up to 90 degrees - so I started the a/c unit. And yes, it was blowing on the controller vents side. With just the a/c on the room didn't cool down very much. So we setup all the fans again, opened the window and door to get a cross vent and ran the a/c on the controller. This managed to keep the room at a steady 84 to 86 degrees through the firing.

In the past 6 years I have never had a problem where the room temp climbs so high. I'm trying to determine what has changed to cause this. I'm thinking that it must have something to do with the lid and heat leaking through the gap into the room. Not sure about the insulation - I will check on that. This studio space is an ongoing project that we keep working on. I'll check with my husband to see if he changed anything with the insulation - I don't think that 's the case.

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neilestrick    1,381

This may sound like a stupid question, but is the portable A/C unit vented to the outside? It needs to be if it's not, otherwise you're just blowing more hot air into the room and getting little to no cooling effect.

 

Kilns put out a lot of heat, whether the lid is cracked or not. The downdraft vent has nothing to to with it, even if it's not centered under the holes in the kiln, and even if the hose between the vent an the kiln is cracked (assuming you have the type with the cup under the kiln and the vent fan NOT under the kiln). The vent pulls air from the kiln to the fan, then pushes air out from the fan to the exterior. If the cup is not under the holes in the kiln floor, then it's only pulling room air, not hot kiln air. If the hose between the kiln and fan is cracked, then it's pulling in room air through the cracks and spoiling the draft at the kiln, and not pulling kiln air. Only if there is a hose between the fan and the exterior that is cracked will it be blowing hot air into the room, or if that hose is blocked. But you would probably smell it if it was blocked up.

 

Small gaps in the lid are normal. It would have to be a very large gap to cause a sudden problem in the heat of the room. What model kiln do you have?

 

I'd be looking at the building rather than the kiln. Did you trim some trees that normally shade the barn or anything like that?

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We vented the a/c out of the barn. We did trim a hedge last fall, however, the problem occurred at night and it was 50 degrees outside. So I don't think it was either of those issues. I did talk to a Skutt technician and he thinks the issue is with the lid not being seated evenly on the kiln. He had me adjust the lid. And suggested that I put some kiln shelves on top of the lid the next time that I run the kiln.

At this point this is the plan I suppose. I will give it a shot and see what happens.

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neilestrick    1,381

A 23x27 inch kiln with 3 inch brick will put out about 14,000 BTU's per hour of heat into the room at cone 6. That's like leaving two average size stove burners on full blast. At cone 04, about 11,000 BTU/Hr.

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JBaymore    1,432

A 23x27 inch kiln with 3 inch brick will put out about 14,000 BTU's per hour of heat into the room at cone 6. That's like leaving two average size stove burners on full blast. At cone 04, about 11,000 BTU/Hr.

 

 

True, but you have to also take into account the (supposed) air turnover rate in that space given the existing ventilation on the BTU / hr. accumuilation in the space? And also minus the heat pump efect of the AC unit in BTU/ hr.

 

And the fact that it diod NOT dop this before. It started suddenly. One firing .....not an issue.... next huge issue.

 

It still does not make sense.

 

 

 

Potterychick....are you saying that SUDDENLY the kiln lid is havi ng this big crack / sealing issue? Cause if it is not that.... then it is not that.

 

 

best,

 

........................john

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I'm guessing that perhaps it's the lid - not sure what else it could possibly be. I'm wondering if my elements are going, the firing did take a lot longer than usual. BUT the kiln had a heavy load - it was packed loosely with wares, but I had 6 1" shelves stacked with plates. SO according to Skutt techy that's a pretty dense load due to the shelves.

I'm starting to wonder if a "vent-a-Kiln" might be helfpul for this problem.

Has anyone ever used one? And do you think it will address this problem?

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atanzey    6

I have a vent-a-kiln that came with my used kiln purchase. While I 'wanted' a bottom mount vent, I couldn't (yet) justify buying another when I have one. I'm fairly happy with the heat removal aspect of it. Part of their sales pitch on their website is that they've been called in to 'fix' overheating rooms with bottom vented kilns. For whatever that's worth!

 

Alice

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GEP    863

I'm guessing that perhaps it's the lid - not sure what else it could possibly be. I'm wondering if my elements are going, the firing did take a lot longer than usual. BUT the kiln had a heavy load - it was packed loosely with wares, but I had 6 1" shelves stacked with plates. SO according to Skutt techy that's a pretty dense load due to the shelves.

I'm starting to wonder if a "vent-a-Kiln" might be helfpul for this problem.

Has anyone ever used one? And do you think it will address this problem?

 

 

Did the overheating problem happen the first time you stacked your kiln like this? If so, the longer firing time could account for all the extra heat in the room.

 

Once, a potter called me freaking out because her kiln (with a kiln sitter) had still not shut off after 18 hours. She hadn't owned the kiln very long, and up until then, her glaze firings had taken about 9 hours. Turns out it was because she had stacked the whole thing with shelves 1 inch apart, to fire tiles. I was surprised at how much more energy it consumed.

 

Can you try another load that does not have as many shelves, and see what happens?

 

I have a vent-a-kiln. My studio will get pretty warm in the summer when firing the kiln, but never over 100 degrees. That could also be because I'm in a basement that tends to stay cool.

 

Mea

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Hmmm... that's an interesting thought. I don't think I've ever stacked so many shelves with so many plates before. I usually have a lot of bowls and mugs and pack it pretty tightly but with only 4 layers of shelves. Sometimes an extra 1/2 shelf with small plates at the top if I can fit it.

I will be running another glaze kiln in a few weeks - I will be sure to put taller items with less shelves in it.

Thank you EVERYONE for all of the input. It's so comforting to know that there are so many potters in the world with so much experience and information.

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neilestrick    1,381

A 23x27 inch kiln with 3 inch brick will put out about 14,000 BTU's per hour of heat into the room at cone 6. That's like leaving two average size stove burners on full blast. At cone 04, about 11,000 BTU/Hr.

 

 

True, but you have to also take into account the (supposed) air turnover rate in that space given the existing ventilation on the BTU / hr. accumuilation in the space? And also minus the heat pump efect of the AC unit in BTU/ hr.

 

 

 

Agreed. Just wanted to give people an idea of how much heat comes off a kiln.

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Bobg    4

The kiln is going to radiate heat even with a vent. The only way you will lower the temp is with fans and/or open the door/windows.

 

Bob

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