People are always asking about element life, so here are my thoughts on that subject:
On my personal kilns I get 150-160 firings out of my elements, doing a combination of cone 04 bisque and cone 6 glaze, probably 35% bisque and 65% glaze. This is true for both my big 21 cubic foot kiln and my small 4 cubic foot kiln, and is consistent from year to year. Both are L&L kilns with standard elements, not quads. I see similar numbers in my customers' kilns of all brands. I have to change the elements in my small kiln every year, in my big kiln every 2 years.
According to my records I've currently got 241 firings on the thermocouples on my small kiln. I should probably check those soon. They do tend to last longer than the elements, though, because they are thicker and are in protection tubes.
Only firing to low fire temps makes a big difference in element life. Today I did a checkup on an L&L E23T that I installed in a school in 2009. They do about 55 firings a year, all low fire- bisque to 04, glaze to 05. The kiln currently has 418 firings on its original elements, relays and thermocouples. The element resistance is almost perfect. Visually they're starting to show their age, though, and I expect that they'll start to degrade more quickly over the next year. I told them to budget for an element change at the end of the 2017-2018 school year. I wouldn't be surprise if they hit 500 firings.
All of this is subject to what's going on in your specific kiln, though. I have a customer who only gets 70 cone 6 glaze firings out of her elements because she does a really long, slow soak at the high end. She could get 100 with a typical firing schedule. The types of glazes you use, and how you load the kiln will also effect element life. Don't put your pots right up against the kiln walls! I'm also convinced that doing a combination of bisque and cone 6 will get you more cone 6 firings than just firing cone 6 all the time. I have absolutely no science to back that up, but my customers who only use their kiln for cone 6 glaze firings tend to get a slightly fewer firings out of their elements.
Maxing out your kiln will cost you. I have a customer who is using their Skutt 1227, 208 volt single phase kiln for cone 5. On that voltage and phase it is only rated for cone 5, so they are maxing out what the kiln can do, and it's definitely costing them. Once the element resistance changes just a little bit, the kiln can no longer get to cone 5 and we have to change the elements. If the kiln was rated for cone 8 or cone 10, it could handle more resistance change before it struggled to get to cone 5. The customer is supposed to be trying some firings to cone 3 with a hold to get to 5. Hopefully that will work out and help with their element life. In my tests, higher temps seem to burn out elements faster than holds.
Keep your elements clean. Vacuum out the kiln occasionally. Monthly would be fine, but definitely any time something blows up. All the little shards on the elements cause hot spots, which lessen the element life. I worked on a kiln at a school once that was only used for low fire pots. The teacher never vacuumed it out when the kids' work blew up, and the bottom element was full of shards, like really full. As we all know, low fire clay melts when it gets too hot. Well, the clay shards caused enough hot spots that all of the shards melted and fused the entire bottom ring of the element into the bricks. It was just a big tube of glass filling the element grooves. I had to replace all of the bricks in the bottom row. $$$
Have a great weekend!