Why that used kiln might not be such a bargain

Most second hand kilns on the market are former pottery kilns.  Good second hand glass kilns are few and far between.  Pottery kilns tend not to be effective as kilns for warm glass work.

Power requirements

Pottery kilns have been designed to be capable of firing to 1200~1300 degrees Celsius.  Most glass work is done around 800 degrees Celsius.  What that means in reality is that for a given volume, a pottery kiln will draw twice the amount of power as a glass kiln.  That power demand generally necessitates large and expensive power circuits.

Shape

 Pottery kilns tend to be relatively tall compared with their area and are often round.  Potters need this to make large 3D pieces and can stack their ware on multiple shelves.  Most warm glass work requires a large shallow area and given the inevitable tmperature variance between the bottom and top of a kiln, multiple stacked shelves of warm glass are rarely possible.  When you consider usable fusing area, a round kiln is generally not as suitable for glass as it doesn’t give you a large working area.

In our experience most warm glass projects are sqaure or rectangular.  A round kiln with a diameter of 45 centimeters (18 inches) will only take a square shelf up to 30 cm (12 inches)

Door Type

Many pottery kilns are front loading (with a door) whereas a top loading kiln (with a lid) is more suited to most warm glass work.  Pottery kilns are rarely opened when hot whereas working with warm glass often requires intervention in the kiln by the artist at various stages during the process.  When you open a front loading kiln there is a chimney effect with hot air rushing out the top and cold air entering from the bottom.  Such a sudden temperature change will often be fatal to your glass, molds and kiln furniture.  Opening a top loading kiln on the other hand allows heat to escape but does not have the same rapid influx of cold air from the bottom.

Safety

A number of imported kilns do not comply with Australian safety standards - in particular allowing the door or lid to be open whilst the elements are still energised - creating a real risk of electric shock.