Gas VS Electric Kiln

[neilestrick]

The age of your elements can dramatically affect the firing cost. I let my last set of element go way too long to see what the affect would be, and my firing cost almost doubled.

@crusty What's your turnup schedule? With a glaze firing if the pots are dry, you can go 1/2 hour on low, 1/2 hour on medium, then high till done.

[Hulk]

Hi Crusty,

Just curious, is your kiln outdoors, else exposed to outdoor temperatures? I haven't analyzed differences in firing rates when studio is ~50F against ~80F; seems like it's faster when the weather's hot ("hot" for here, lol! studio will hit high nineties, easy, with kiln on and all doors open).

Any road, I'm running my manual kiln up to about 250F the night before, hence should be thoroughly dry the next day, then full bore (all three switches on high)  until target temp is achieved (cone 6); then I'm dropping the temp 120F or so and holding there for forty minutes, then all off. 

The elements ( 7 cubic foot Skutt, over thirty years of service, so far, second hand to me...) are at least half tired - takes about eight hours to reach cone 6 from 120F.

Fuddling with the switches, somewhere between what a pain and it just requires attention, eh? Bisque fire requires much more fiddling, as there are a few temperature zones to pause in, especially with that red clay...

[Min]

5 hours ago, Crusty said:

it's the J230 , 10,500 watt , 240 Amp

I did the numbers by hand and with the firing calculator. (0.12) X (10.5) X (12) X (0.65) = $9.82  (using 12 cents as the cost per kilowatt hour, wattage at 10.5, 12 hour firing and running 65% duty cycle. The calculator version came in at $9.01 (using same parameters) so pretty close. (I'm guessing you meant 240 volt not amp)

Have you ever checked the resistance of your elements?

@Mark C., wow, expensive electricity in your part of the world! Need to run an extension cord up to Callie in Alberta. 

[Crusty]

Neil my elements were shot. I cant remember the exact ohm reading but the person I talked to said , yea your really out of range..  my new ones came yesterday, I got the HD as they said they should last longer..

Hulk I'm indoors in a basement.. 

[Crusty]

Neil we turn the kiln up slowly, we read that 250 a hr was a good temp rise .. honestly though, I see gas kilns pushing 350 and more.. I kinda babysit ours ..  I'll try a faster ramp ..

[liambesaw]

3 minutes ago, Crusty said:

Neil we turn the kiln up slowly, we read that 250 a hr was a good temp rise .. honestly though, I see gas kilns pushing 350 and more.. I kinda babysit ours ..  I'll try a faster ramp ..

Here's the standard Bartlett controller schedule so you can see what a computer would do, this is cone 04 but adding extra cones only effects the length of the middle segment:

 

[Chilly]

8 hours ago, Callie Beller Diesel said:

You're all going to hate me. I pay .068 per kilowatt hour. Or I did in September. I have a variable rate. It goes up in the winter, but I'd have to go digging for other bills.

The advantages of living in a province with lots of oil.  We liked visiting Alberta, only one lot of tax, unlike BC or Manitoba.  

[liambesaw]

1 minute ago, Chilly said:

The advantages of living in a province with lots of oil.  We liked visiting Alberta, only one lot of tax, unlike BC or Manitoba.  

Plus they've got that Berta beef

[Crusty]

2 hours ago, liambesaw said:

Here's the standard Bartlett controller schedule so you can see what a computer would do, this is cone 04 but adding extra cones only effects the length of the middle segment:

 

Thats nice. i guess we been taking it to easy to slow .. ill get the new elements in saturday or sunday and try a bisque on monday..  im still going slow until 250 F though.. dont need to lose any pots LOL...

[Min]

 

13 minutes ago, Crusty said:

Thats nice. i guess we been taking it to easy to slow .. ill get the new elements in saturday or sunday and try a bisque on monday..  im still going slow until 250 F though.. dont need to lose any pots LOL...

With a firing to condition the elements before the bisque fire?

[Bill Kielb]

On 11/13/2019 at 7:41 PM, Crusty said:

Thats nice. i guess we been taking it to easy to slow .. ill get the new elements in saturday or sunday and try a bisque on monday..  im still going slow until 250 F though.. dont need to lose any pots LOL...

Just a word of caution, the schedule above is for glaze, you seem to be saying bisque. Generally bisque schedules run 10 to 12 hours and go a bit slower than the 400 degree per hour you see above. Bisque firings are generally slower and many claybodies need sufficient time at temperature to burn out their organics.

sample bisque schedule below. Even the fast bisque is over 10 hours

 

[Mark C.]

4 hours ago, Min said:

I did the numbers by hand and with the firing calculator. (0.12) X (10.5) X (12) X (0.65) = $9.82  (using 12 cents as the cost per kilowatt hour, wattage at 10.5, 12 hour firing and running 65% duty cycle. The calculator version came in at $9.01 (using same parameters) so pretty close. (I'm guessing you meant 240 volt not amp)

Have you ever checked the resistance of your elements?

@Mark C., wow, expensive electricity in your part of the world! Need to run an extension cord up to Callie in Alberta. 

thats why I have a small commercial user gas account  the past 47 years.And have 3 gas kilns..

[Callie Beller Diesel]

9 hours ago, Hulk said:

Hi Crusty,

Just curious, is your kiln outdoors, else exposed to outdoor temperatures? I haven't analyzed differences in firing rates when studio is ~50F against ~80F; seems like it's faster when the weather's hot ("hot" for here, lol! studio will hit high nineties, easy, with kiln on and all doors open).

...

Mine’s outside in a tin garden shed, and I get a pretty wide temperature swing. The coldest I’ve fired in is -25/30 -ish C, and if it took much more than half an hour to finish than in summertime, I didn’t notice. 

 

And before anyone cracks any jokes, summertime averages are 25 C on the plus side. 

[Crusty]

1 hour ago, Min said:

 

With a firing to condition the elements before the bisque fire?

yes. 

[liambesaw]

34 minutes ago, Callie Beller Diesel said:

Mine’s outside in a tin garden shed, and I get a pretty wide temperature swing. The coldest I’ve fired in is -25/30 -ish C, and if it took much more than half an hour to finish than in summertime, I didn’t notice. 

 

And before anyone cracks any jokes, summertime averages are 25 C on the plus side. 

Also have never noticed a difference between the seasons other than if I do a preheat on the controller it takes about 30 minutes longer to reach 200 on account of the starting temp being lower.

Firing outside is awesome

[Crusty]

1 hour ago, Bill Kielb said:

Just a word of caution, the schedule above is for glaze, you seem to be saying bisque. Generally bisque schedules run 10 to 12 hours and go a bit slower than the 400 degree per hour you see above. Bisque firings are generally slower and many claybodies need sufficient time at temperature to burn out their organics.

sample bisque schedule below. Even the fast bisque is over 10 hours

thanks , I was at work and it was a crazy day..  I saved both schedules..  I also purchased a pyrometer to help us out ..  it gets old looking into the kiln to see the black spots LOL.  

[Crusty]

Just now, liambesaw said:

Also have never noticed a difference between the seasons other than if I do a preheat on the controller it takes about 30 minutes longer to reach 200 on account of the starting temp being lower.

Firing outside is awesome

Simon Leach swears by a cooler air temp after a glaze firing. he says it makes his colors pop more.  I get in the 60s in my basement. hes in a garage, could be even cooler..

[Bill Kielb]

48 minutes ago, Crusty said:

Simon Leach swears by a cooler air temp after a glaze firing. he says it makes his colors pop more.  I get in the 60s in my basement. hes in a garage, could be even cooler..

Cooler air definitely can freeze a glossy glaze as gloss. Much in the same way slow cool promotes crystal growth and muted mattes. We often add a little boron to cone ten celosia red in reduction just because high gloss makes the red pop that much more.

Cool air tough on gas firing though. Gotta heat up every cubic foot that goes through the burner as well as any secondary air. Energy waster!

[neilestrick]

I used to fire wood kilns in the dead of winter in Utah, and there was never any difference from the summer. Once the kiln is warm, the outside air doesn't affect things during the firing. Where it can be an issue is the final cooling, like once you're down to oven temps. If you start letting freezing air in it can cause problems.

[Bill Kielb]

1 hour ago, neilestrick said:

I used to fire wood kilns in the dead of winter in Utah, and there was never any difference from the summer. Once the kiln is warm, the outside air doesn't affect things during the firing. Where it can be an issue is the final cooling, like once you're down to oven temps. If you start letting freezing air in it can cause problems.

Hmm, interesting,

Lots of cold air to heat up on the way to being burned as well as bigger structure losses while firing.  Maybe not noticeable or maybe different physics, LOL?  Well anything is possible I guess, after all most people weigh  50-100 grams less In Utah than in  Concord New Hampshire so maybe .............

[liambesaw]

39 minutes ago, Bill Kielb said:

Hmm, interesting,

Lots of cold air to heat up on the way to being burned as well as bigger structure losses while firing.  Maybe not noticeable or maybe different physics, LOL?  Well anything is possible I guess, after all most people weigh  50-100 grams less In Utah than in  Concord New Hampshire so maybe .............

Probably not noticable.  I'd assume the firebox would act as a buffer zone while the entire glowing kiln would act as a sort of heat exchanger on the surrounding area. After all, wood firing is one of the more wasteful energies.  

[Bill Kielb]

@liambesaw
Ideally 1  pound of wood to about 7 pounds of air or more realistically 10 pounds of air. That’s a lot of  air (energy) but in reality in the winter the humidity will be much less so the difference in enthalpy maybe not so great. The difference between cold for humans is only 70 degrees, so not real relevant at two thousand degrees even though we think it’s cold.. So probably a a little more in combustion and a reasonable amount more in conduction losses. 

So the  perception that it makes little difference  is probably fine. Wood is heavy, an extra hundred pounds? Who would notice.

In a gas kiln  you are limited to the amount of energy you have and peak flame temperature. With wood, just add more, 8000 - 9000 btu per pound.  Softwood produces more energy than hard wood BTW. 
 

Good campaign on the internet BTW raise 20 million dollars and plant 20 million trees by 2020.  Trees are made primarily of carbon and burning all that lumber releases all that energy accumulated during growth. Maybe a decent way for potters to do a part  for Mother Earth. Seems like a solid idea in my opinion.

[liambesaw]

3 minutes ago, Bill Kielb said:

@liambesaw
Ideally 1  pound of wood to about 7 pounds of air or more realistically 10 pounds of air. That’s a lot of  air (energy) but in reality in the winter the humidity will be much less so the difference in enthalpy maybe not so great. The difference between cold for humans is only 70 degrees, so not real relevant at two thousand degrees even though we think it’s cold.. So probably a a little more in combustion and a reasonable amount more in conduction losses. 

So the  perception that it makes little difference  is probably fine. Wood is heavy, an extra hundred pounds? Who would notice.

In a gas kiln  you are limited to the amount of energy you have and peak flame temperature. With wood, just add more, 8000 - 9000 btu per pound.  Softwood produces more energy than hard wood BTW. 
 

Good campaign on the internet BTW raise 20 million dollars and plant 20 million trees by 2020.  Trees are made primarily of carbon and burning all that lumber releases all that energy accumulated during growth. Maybe a decent way for potters to do a part  for Mother Earth. Seems like a solid idea in my opinion.

That's actually perfect for wood firers, you can't reverse or sequester the carbon from burning oil and natural gas (yet), but you can turn the carbon from wood firing back into wood.

[neilestrick]

3 hours ago, Bill Kielb said:

In a gas kiln  you are limited to the amount of energy you have and peak flame temperature.  With wood, just add more, 8000 - 9000 btu per pound.  Softwood produces more energy than hard wood BTW. 

 

I think you're backwards there. Hardwoods will generally produce more heat and burn longer, because they are more dense.

I don't agree that for firing with wood you can just add more wood to get more heat. There is some truth to that, but it's just like saying turn up the gas to get more heat. But just like a gas kiln there is a limit to how much fuel, air, and draft you have to work with in order to get the combustion to work. More wood does not directly correlate to more heat, and it's pretty easy to overload the firebox. There is a finite amount of combustion air available in a wood kiln, just like a gas kiln.

[Bill Kielb]

33 minutes ago, neilestrick said:

I think you're backwards there. Hardwoods will generally produce more heat and burn longer, because they are more dense.

I don't agree that for firing with wood you can just add more wood to get more heat. There is some truth to that, but it's just like saying turn up the gas to get more heat. But just like a gas kiln there is a limit to how much fuel, air, and draft you have to work with in order to get the combustion to work. More wood does not directly correlate to more heat, and it's pretty easy to overload the firebox. There is a finite amount of combustion air available in a wood kiln, just like a gas kiln.

Hmm,

Per  pound, softwood generally has more btu than hardwood and my guess would be if you need more btu you will use more wood especially if you suck in colder air and lose more heat due to radiation loses. we preheat boiler air for this very reason. Now as to the weight of the wood, that is a different story. Moisture content is huge, stacking ability another issue or overstacking as you say. As far as energy in comparison, softwood generally has more Energy per pound than hardwood. I don’t think that’s backwards actually. if you need more btu because your losses are higher you will need to burn more pounds of wood, soft or hard.

The Softwood misunderstanding  is often thought to originate  from having too much tree sap and creating  creosote issues.