How Much Did That Last Firing Really Cost?
Copyright (c) 2001 by Beverly Howard, Austin, TX, USA

First, a note of Caution... Electricity is LETHAL!  The following information is provided for those who are knowledgeable, experienced and comfortable working with and around 240 volt ac electrical systems and high temperature ceramic kilns.  If you are not, please do not attempt to implement any of the following suggestions without the help and assistance of a licensed electrician.

In addition to the electrical dangers, electrical and firing problems can easily lead to accidental fires that can destroy structures not to mention the possibility of killing or injuring people.  While the author has executed the following modifications and those modifications are currently in use in a full time pottery studio at the time of this writing, the author does not accept any responsibility for any injury, damage or other losses that may result from attempting to implement any of the suggestions and designs shown in the following page.  The use and implementation of these suggestions are at your own risk.

While the new computer based kiln controllers helpfully display the total length of the your last firing, knowing the time the firing required really doesn't help to determine how much the firing cost with respect to the actual amount of the kilowatt hours of electricty consumed.  The reason that it doesn't is that the controller constantly controlled the amount of heat by turning the elements on and off throughout the firing, so, while the firing time might have been 18 hours, the time the kiln was drawing electricity was significantly less due to the controller switching on/off during that firing period.

Building a Firing Clock Timer

It's fairly simple to rig an "Element Timer" in any kiln which uses a single controller box that will allow you to quickly and easily determine the precise amount of  hours the firing consumed electricity... the key component for measuring element on time is an old fashioned electric clock.  I will note here that these have become scarce in the twentyfirst century, but they can be found... sometimes in second hand shops or goodwill.

In almost all kilns, the elements are wired to accept 220v-240v from a "two phase" electrical supply.  Each side of the element is at 110v-120v with respect to neutral, so, it's simple to install a 110v receptacle that is wired with the receptacle's hot lead to one side of an element supply and the other to neutral.  (You may have to run a small neutral lead to the kiln)

Once wired, take any 110v electric clock and set the time to exactly 12 oclock, then plug it into this special receptacle before the firing starts.

Since the receptacle will only provide power to the clock when the elements are on, when the firing is finished, the clock will have run an amount of time which is somewhat less than the total length of the firing, so, if the time reads 10:37 after the firing, the kiln was powered on for ten hours and thirty seven minutes even though the firing may have taken 18 hours from start to shutdown.

Kilowatt Hour Calculations

Time to pull out the electric bill.  The simplest way to determine your cost per kilowatt hour is to divide the bill by the amount of kwh consumed.  However, in many cases, the electrical rate charged varies by factors such as when the electricity was consumed...

In Austin, Texas, For example, the first 500 kwh in a month's electricity billing costs far less than amounts consumed after the first 500 kwh, so, since kilns are big consumers, to be accurate, their cost should fall into this second block, which, in Austin, at this writing (2006) is $.1137 ...almost double the cost of the first 500 watts.  (update... in 2010, it's $.0967)

The other two variables needed to complete the electrical consumption calculation are voltage and amperage.


Determining the voltage is fairly simple... measuring it with an accurate voltmeter at any available 220v outlet will suffice. 


To get the amperage, you will need an "amprobe" clamp on ampmeter and access to one of the kiln supply wires during the firing.  You can use the amperage shown on the kiln's data plate, but, if you do, know that it may be off by 25% or more.

If you use a KilnMaster kiln controller built since 3/06, you probably have a built in amperage sensor that you can use to determine the amperage for each kiln section... simply add the amperages for all of the sections together to determine the total amperage the kiln uses when firing.  In the Skutt manual, this feature is described in the "Menu Features/Diagnostics/Amps" section.

The Formula

Once you have those figures, the formula to calculate the total electrial cost of any firing is;

(Amps X Volts) / 1000  X  "Cost Per Kwh" X Hours

Responses, implementations, comments and suggestions appreciated.  Email me at

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