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Firing Your Electric Kiln Can Be Very Expensive


All kiln manufacturers encounter this thought with customers. However, the reality is much different even with the increased cost of electricity in the last few years. The firing cost for glass kilns is lower than most customers believe.Here is the basic information needed to calculate the firing costs of a kiln. After the formula are two examples applying the formula to typical kilns operated by artists.

To calculate the firing cost we need to understand the formula:

(cost per kilowatt hour charged by electric company) x (kilowatt rating on kiln) x (the number of hours the kiln takes to complete a firing) x (the duty cycle of the kiln)

The electric company charges for power in kilowatt hours. Electric costs range from $.10 to $.20 per kilowatt hour depending upon your location. The cost per kilowatt hour can be found on the bill from your power company.

The kilowatt rating of the kiln can be found on the electrical data plate located on the side of the control box on the kiln. The data plate has the volts, phase, amps and watts. Most of the small introductory kilns that operate on 120 volt standard household outlets have about 1500 to 1800 watts or 1.5 to 1.8 kilowatts. The medium sized kilns that are about 17-23 inches wide are rated around 5.0 to 8.0 kilowatts. Some large glass kilns can be rated around 11 kilowatts. To convert watts on the data plate to kilowatts, divide the watts by 1000.

The number of hours the kiln fires is displayed on the digital controller at the end of the firing. The firing time can be under an hour to 20 hours depending upon the project. If the kiln does not have a digital controller, just measure the time from start to when you turn off the kiln.

The duty cycle for the kiln is the amount of time the elements are actually having electricity going through them. Electricity is only going through the elements when the relays are ON. This is the clicking or humming sound heard when the kiln is operating. The kiln is using electricity only when the relays are ON. The general duty cycle for firing of glass kilns with HOLD times, controlled ramp rates, etc is 50-60%. For example, if the fusing program takes about six hours, the relays are only ON for about 3-4 hours of that six-hour firing.

Here are two examples applying the formula to the firing of two kilns.

EXAMPLE #1
Small glass kiln that operates on standard household 120 volts and is rated at 1700 watts or 1.7 kilowatts. Firing program is a fast fusing with a total firing time of 1 hour and 30 minutes. That is 1.5 hours. A duty cycle of 60% is assumed.

Putting this information together with a cost per kilowatt hour of $0.12, the formula looks like this:

$0.12/KwHr x 1.7 Kw x 1.5 hours x .6 = $0.18.

Therefore the cost of firing a small glass kiln with a 1.5 hour fusing program is about $0.18 when the cost per kilowatt hour is $0.12. Here is a table showing the firing costs at different costs per kilowatt hour.

FIRING COSTS FOR 1.7 KILOWATT KILN Example #1

  • Cost per Kw Hr: $0.10, Cost per firing: $0.15
  • Cost per Kw Hr: $0.12, Cost per firing: $0.18
  • Cost per Kw Hr: $0.14, Cost per firing: $0.21
  • Cost per Kw Hr: $0.16, Cost per firing: $0.24
  • Cost per Kw Hr: $0.18, Cost per firing: $0.28
  • Cost per Kw Hr: $0.20, Cost per firing: $0.31


EXAMPLE #2
Medium glass kiln that operates on 240 volt circuit and is rated at 7000 watts or 7.0 kilowatts. Firing program is a basic fusing program with a total firing time of 8 hours and fifteen minutes. That is 8.25 hours. The program includes some controlled ramps and hold times. A dusty cycle of 60% is assumed.

Putting this information together with a cost per kilowatt hour of $0.12, the formula looks like this:

$0.12/KwHr x 7.0 Kw x 8.25 hours x .6 = $4.16.

Therefore the cost of firing this program in this kiln is about $4.16 when the cost per kilowatt hour is $0.12. Here is a table showing the firing costs at different costs per kilowatt hour.

FIRING COSTS FOR 7.0 KILOWATT KILN Example # 2

  • Cost per Kw Hr: $0.10, Cost per firing: $3.47
  • Cost per Kw Hr: $0.12, Cost per firing: $4.16
  • Cost per Kw Hr: $0.14, Cost per firing: $4.85
  • Cost per Kw Hr: $0.16, Cost per firing: $5.54
  • Cost per Kw Hr: $0.18, Cost per firing: $6.24
  • Cost per Kw Hr: $0.20, Cost per firing: $6.93


The costs are generally less than most people expect. There is no change to the cost per firing if the kiln uses three-phase power, because the kilowatt usage remains the same. Firing with large amounts of glass has only a marginal impact on the firing cost.

Some customers do not need to perform these calculations as some of the controllers provided by the kiln manufacturers have the capability now to calculate the firing cost of each firing. The customer just needs to enter the cost of their electricity, and the controller does the rest. At the end of the firing, the customer presses a button and the firing cost is displayed.

Hopefully the explanation and the examples offer an understanding of how to calculate the firing costs.

Article written by John Hohenshelt of Paragon Kilns

Last updated on Fri, July 24, 2009 by Metal Clay Guru