Are you not talking nonsense!!!! read the Klin manufacturer's manual, take an infra-red gun temperature indicator and find out where you stand.Your Control panel Room will have all indicators and recorders and the guys there are recording hr-hr changes on all parameters unless, ofcourse you are not authorized in this area.

Thanks for your response. The Kiln manufacturer's manual makes no reference, and we have not seen a glow on the shell. Hence your suggestions will not help at this stage.

One of my hobby books states that when bright orange the inside of a furnace is typically about 1700 F. I don't know how accurate it is, but this would suggest that the dull glow would be a bit under 1700 F. How far under I don't know.

Glow of steel probably starts at about 1200 deg F but it is dependant on things like the actual alloy. The suggestion to check it with an infrared heat gun is a good one.

Depending on the kiln design, a blow out may be imminent. Depending on what shoots out (burning natural gas) and what may be close to the kiln this could be very dangerous.

If your kiln is refractory lined it sounds like it is time to shut it down and do a reline. Or maybe your burn profile is off. Whatever the reason, likely your kiln shell is way too hot if you see a glow.

http://en.wikipedia.org/wiki/Color_temperature

Heat treat furnaces that I watched for a couple years ran at 1625 degrees Fahrenheit. Red hot.

put a series of pyrometric cones on the shelf, these cones are calibrated to bend at different tempratures.: http://www.ortonceramic.com/