How much a firing costs
An electric kiln draws its full rated power only while its elements are on. During a firing program the controller switches them on and off to follow ramps and holds, so the average power over a firing is well below the nameplate figure: typically 45 to 65%.
The formula
kWh per firing = kiln power (kW) × firing hours × average duty
Cost per firing = kWh × electricity price
Dividing by the number of pieces in the load gives the cost per piece, a useful figure for pricing pottery.
Example
A 240 V kiln rated at 11.5 kW fires for 9 hours at an average of 55% of its power: 11.5 × 9 × 0.55 = 56.9 kWh. At $0.17 per kWh, the firing costs $9.68, or $0.48 per piece for a load of 20 pieces. Four firings a month cost about $39.
| Firing | Typical duration | Typical average duty |
|---|---|---|
| Slow bisque, cone 04 | 8 to 12 h | 40 to 50% |
| Glaze, cone 06 to 04 | 6 to 9 h | 50 to 60% |
| Glaze, cone 5 to 6 | 8 to 11 h | 55 to 70% |
Reading your kiln’s real consumption
The most accurate way is to read your electricity meter before and after a firing, or to use the kWh counter some controllers display. Old elements take longer to reach temperature, which raises both the duration and the duty; when a firing that took 9 hours now takes 11, it is time to replace the elements.
Electrical supply
A kiln is a continuous load. The current at full power is power ÷ voltage: 11,500 W ÷ 240 V = 47.9 A. The US National Electrical Code requires the circuit to be sized at 125% of a continuous load, so this kiln needs a 60 A breaker and matching wire. Always follow the manufacturer’s installation sheet and have an electrician check the circuit.
Saving energy
- Fire full loads: a half-empty kiln costs almost as much as a full one.
- Combine bisque and glaze firing schedules to avoid half-loads.
- Keep the lid and peepholes closed after the water-smoking stage.
- Check that the kiln’s lid and walls are not cracked; heat leaks raise the duty.