A friend of mine tells me that the engine does not have to be running for the heat to work in the vehicle. I have tried to tell him that it does have to have the engine running in order for the heat to work. Correct me if I am wrong. Or tell me that I am right so I can show my friend that I am correct.
Thank you for writing in. If you want the heater to blow warm air, the engine needs to be running. The vents will blow air without the engine running when you are in accessory mode, but without the heater core receiving hot coolant from the engine the air is not heated as it is blown into the cabin. You are correct, and traditionally all vehicles use a heater core filled with hot coolant from the engine to warm the air. Show your friend a diagram of a Mitsubishi Galant heater system for an example of why that is.
Now, with that said, electric vehicles are a little different. Tesla for example has specific batteries for the heating system, because they do not have an actual engine that requires traditional coolant. To my knowledge, you can run a Tesla's heater without the vehicle "running", but this is relatively new technology to the mainstream automotive markets.