In car wired Block Heater?

[Eggman]

I would think the Kats heater is nothing more than a nichrome resistance wire in a tube. If so, AC or DC is irrelevant. It will heat regardless of the power source.

Just have to figure out if enough current will flow from a 12v source to heat the element.

I think you're right. Whatever it's made of, a direct or alternating current source should not affect it's operation.

However, the unit is designed to resist 120VAC enough to allow so much current to pass in order to achieve a certain power rating in watts. If the voltage provided is one tenth that of design, the wattage (and thus heat) will be reduced accordingly.