Heat transfer
Vol. 22 #2, Sept. 1995
Before start up, check to make sure the heaters are in direct contact with the barrel surface.
Air is a great insulator, and gaps between heater and barrel make the heater work that much harder and burn out that much sooner.
See also
Barrel heaters
Barrel zone override
Gauge variation
Heater contact
Heat exchanger
Start up 2
Trouble shooting with barrel zones