Because of the little drawback of having the engine idle to heat up to an optimum temperature for heating the interior, I'm thinking I might utilize the rear (trunk) power outlet and with a power inverter plug in an electric heater/fan for the car. That way I can minimize using the heat for only the defrost. Any thoughts? And just for information's sake, here in Minnesota the temperature drops to -20 to -30.

 

If you want to use an electric heater you might consider buying a 12 volt heater to eliminate the complexity of an inverter. Just search "12 volt heater".



I'm, not sure you will save fuel with this approach though it might help you comfort wise before the engine is warmed up.



The engine is much more efficient at producing hot water for the normal heater system than it is in producing electricity for an electric heater. Over 70% of the gas consumed by the engine is turned into waste heat dissipated by the engine, radiator, engine exhaust, and the heater core. Once the engine is warmed up, any heat not consumed by the interior heater core is just dumped outside via the radiator.



I would recommend an engine block heater run about 3 hours on a timer before you leave in the morning (if you have access to an electrical outlet where you park). This will get the engine warmed up faster and save fuel.

 

Engine block heater - it will be the most efficient and economical.

Somewhere on this site there is a link to an installation with instructions.

 

BlueHeat® How BlueHeat Works Heat the interior or the engine and interior No pluging in ,remote, uses gas,saves engine

 

Why not install a 4-way valve so the A/C compressor can be used as a heat pump or air conditioner?