How much heat is lost through a kiln’s bead doors when bead mandrels are inside the kiln?
With bead mandrels extending out past the bead door of a kiln, there is some loss of heat, but it is minor.
Electricity costs about $0.13 per kilowatt hour. This means you have to run a 1000 watt device for one hour to use $0.13 of electricity. Most annealing ovens turn on the elements for only about 50% of the time they operate. You can tell when the elements are on by clicking ON and OFF of the relay. The kiln pulls the kilowatts only when the relays/elements are ON. Most bead annealing ovens are 120 volt and rated to around 1.5 kilowatts. So if the oven pulls power for one straight hour, the cost is about $0.20. (1 hr x $0.13 x 1.5Kw).
If the elements are only on 50% of the time the cost is $0.10 of electricity per hour of firing. If the kiln runs for four hours and then turns off to naturally cool the beads, the cost is only about $0.40 for the entire firing. So, the amount of heat lost through the open bead doors cannot amount to much. Even if the open doors require 20% more energy to maintain the heat, the duty cycle goes to 60% and the total cost of the four hour firing is increased by $0.08.