# How To Calculate the Cost of Firing Your Kiln

#### Learn how to calculate the cost of firing your kiln and discover how affordable it is and know how to more accurately price your jewelry items.

Last edited: 9/17/2019

The cost of firing a kiln will depend on several factors, such as the charge assessed by the electricity provider, the power drawn by the kiln, the duration and makeup of the firing program being performed, the number, size and composition of the pieces being fired. Understanding the cost kiln firing can help you make a buying decision and help you make smart choices about pricing your jewelry. Use this formula to calculate your costs.

Cost per kilowatt-hour (1)

x Kilowatt rating of kiln (2)

x Program duration in hrs. (3)

x Duty cycle of the kiln (4)

= Cost of firing program

Providers of electricity charge for power in kilowatt (kW) hours. The cost per kW-hour ranges from approximately \$0.10 to \$0.20 depending on location. This rate is shown on the provider’s monthly bill.

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 shows the volt, phase, amp and watt capacities of the kiln. Most smaller, introductory kilns that operate on 120-volt standard household outlets draw about 1500 to 1800 watts. Medium-sized kilns (17"–23"W) are rated around 5000 to 8000 watts. Some large glass kilns can be rated as high as 11,000 watts. To convert the watts shown on the data plate to kilowatts, simply divide the watts by 1000: 1500 watts = 1.5kW; 8000 watts = 8.0kW.

The program duration is the number of hours the kiln fires to complete its program. This elapsed time is displayed on the digital controller at the end of the firing cycle. The firing time can be less than an hour or up to 20 hours, depending on the project. If the kiln does not have a digital controller, just measure the time from starting the kiln to when you turn off the kiln.

The duty cycle for the kiln is the amount of time the elements are actively drawing electricity. Electricity is going through the elements ONLY when the relays are ON. The clicking or humming sound heard when the kiln is operating is a clear indictor that the relays are ON and the kiln is actively drawing power. Generally, the duty cycle for firing of kilns with controlled ramp rates, hold times and so on, is roughly 50%–60%. During a program that takes about six hours, the relays will only be actively on, drawing power, for about 3–4 hours.

Example #1

In an area where the cost per kW-hour is \$0.12, a small-sized kiln operates on standard 120-volt household power and is rated at 1700 watts (1.7kW). The firing program is a fast fusing of glass with a total firing time of 1-1/2 hours. A duty cycle of 60% (0.60) is assumed. Putting this information together, the formula looks like this:

\$0.12 cost/kW-hr.

x 1.7 kW rating

x 1.5 hrs. duration

x 0.6 hr. duty cycle

= \$0.18 cost of firing program

Here is a table showing the firing cost for the same kiln and program at different costs per kilowatt-hour:

Cost/kW hr. = Cost of Firing

\$0.10/kW hr. = \$0.15

\$0.12/kW hr. = \$0.18

\$0.14/kW hr. = \$0.21

\$0.16/kW hr. = \$0.24

\$0.18/kW hr. = \$0.28

\$0.20/kW hr. = \$0.31

Example #2

In an area where the cost per kW-hour is \$0.12, a medium-sized kiln operates on 240-volt power and is rated at 7000 watts (7.0kW). The firing program is a basic firing for BRONZclay with a total firing time of 9.5 hours, including ramp and hold times. Again, a duty cycle of 60% (0.60) is assumed. Putting this information together, the formula looks like this:

\$0.12 cost/kW-hr.

x 7.0 kW rating

x 9.5 hrs. duration

x 0.6 hr. duty cycle

= \$4.79 cost of firing program

Here is a table showing the firing cost for the same kiln and program at different costs per kilowatt-hour:

Cost/kW hr. = Cost of Firing

\$0.10/kW hr. = \$3.99

\$0.12/kW hr. = \$4.79

\$0.14/kW hr. = \$5.59

\$0.16/kW hr. = \$6.38

\$0.18/kW hr. = \$7.18

\$0.20/kW hr. = \$7.98

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