Well, I got mine from eBay. It's a Katt's 800w tank style heater. Thermosyphon style circulation.

There is probably an OEM block heater for the Aveo as well that may require you to pull a frost plug out and install it directly in the water jacket. But, again, I'd only do this if the wattage of the heater is decent.

That way, 45 - 60 min is all you need for a decent amount of heat, eg (for a 1.0L engine)...