The cost of electricity is figured in kilowatt-hours (KWh). A kilowatt-hour is 1,000 watts of electricity running for 1 hour. (10 – 100-watt light bulbs glowing for one hour consume 1 KWh of electricity.)
To find what the power company charges you for a kilowatt-hour, look at your electric bill, call your power company, or visit their website. The electric rate usually varies depending on the time of year and amount of electricity you use. In the summer, rates in most areas are higher. Also, add the other costs listed on your electric bill, such as power transmission charges, taxes, etc. In some areas electricity is less expensive during low-demand times, such as nights and weekends. Call your power company to see if this is available where you live.
Look at your kiln’s electrical data plate. It is usually on the side of the switch box. The data plate lists the watts, amps, and volts. If watts are not listed, multiply amps x volts. (Example: 15 amps x 240 volts = 3,600 watts.)
Divide the wattage of your kiln by 1000, which gives the kilowatts. (Move the decimal point 3 spaces to the left.)
10,800 watts ÷ 1000 = 10.8
4,800 watts ÷ 1000 = 4.8
800 watts ÷ 1000 = .8
To figure kilowatt-hours for your kiln, multiply the kilowatts by the number of hours that all the elements are turned on.
If the heating elements for a 10.8 kilowatt kiln stay on continuously for 5 hours, the kiln would use 10.8 x 5 kilowatt-hours.
10.8 x 5 = 54 KWh (kilowatt-hours)
However, the heating elements do not stay on throughout the firing. If your kiln uses infinite control switches or a digital controller, the elements cycle on and off to control the heating rate. The clicking noise that you hear during firing is the sound of the switches or relays turning the elements on and off.
The faster or hotter your kiln fires, the longer the elements stay on per hour. As a rough rule of thumb, figure that the elements stay on 1/2 – 3/4 of the total firing time.
A kiln draws 10,800 watts and the firing lasts 5 hours. You estimate that the elements remain powered during half the firing.
10,800 watts ÷ 1,000 = 10.8 kilowatts
10.8 x 5 hours = 54 KWh (kilowatt-hours)
54 ÷ 2 = 27 KWh used during a 5-hour firing