hey many car 12 volt caramic heaters claim they can heat up your windsheld faster than your car can warm up. If this is true don't you think this method is a better way to conserve fuel than using the car heater? So instead maybe I can turn the car's thermostat to cold and by not asking the car to give heat maybe the fuel savings will pile up in the winter while the cermaic heater happily defrosts my windsheld drawing amps from the 12v.

Question is, how does using 12volt affect fuel economy?

 

You could probably figure it out by knowing how much power or current the 12 volt heater will draw from the system. Power (watts) = Current (I) x Volts (V). It's probably going to blow your accessory fuse but you can figure about a 1 hp drain for each 750 watts of power you draw. Not to mention that the computer may interpret the power loss as significant and disable the auto stop.

I would think an approximate guess is about 200 Watts. FE could possibly suffer about as much as running the AC intermittently in summer or to defog the windshield or leaving your headlights on all the time.