Built-in prius car heater at -20° F? Hi,
I just wanted to ask if it's okay to run car heater continuously for 12 hours while the car is idle but ignition is on and in ready to drive position.

I know that it will burn gas. That is okay with me. I just want to know if it will cause damage to the engine or transmission. Sorry my car knowledge is non-existent.

I will need to do this every night. Run the car and the heater continuously every night for 12 hours. And as I see the weather, it will remain in the negative teens for a couple of weeks at least.