[dalola]

Mr. Gibbs,
You are correct, in that the sensor must achieve a minimum operating temp of around 400F to function properly. It is at these temps(and higher), the electrolyte becomes conductive and generates a characteristic galvanic charge, and this voltage is an index of the gas oxygen content. Heated sensors reach this temp much quicker, and will maintain optimum temps as well. If you need continuous imput from your O2(computor controlled EFI engines), then heated may be the way to go. On carburated engines, when O2's are used for tuning purposes, you would only need heated sensors if the exhaust gas temp was not sufficient once at normal engine operating temps. If unsure, I suppose it would be wise to error on the heated side.

Dave