Heat press beads

Estimating Heat Loss Through Bead Doors No. 375

Estimating Heat Loss Through Bead Doors

The Paragon BlueBird Jr has two bead doors.


Estimating Heat Loss Through Bead Doors

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By John S. Hohenshelt, President of Paragon

Many people are concerned about the doors of bead annealing kilns being partly open when the rods are placed inside the kiln. The concern is the amount of heat that is lost around the door. There will be some loss of heat, but it is very minor. Here is the analysis.

Electricity costs about $0.13 per kilowatt hour. This means you have to run a 1000-watt device for one hour straight to use $0.13 of electricity. Most annealing ovens power the heating elements for only about 50% of the time they are "ON". This is easily observable by the 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 devices that are rated 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 for one hour of firing. So if the bead artist has the kiln running for four hours and then turns it off to naturally cool the beads, the cost is only about $0.40 for the entire firing. Once this is understood, 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.

Hopefully this explains why having the bead doors slightly open for annealing should offer little concern for the bead artist.


“Firing Glass Visually, ” the last Kiln Pointer, was about checking the hot glass through a kiln peephole or window. Julia Larson, a glass artist in St. Petersburg, Florida wrote, “I have a pendant...

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