Ignoring the fact that your entire post is based on an incorrect assumption (The volt is not an Electric-only car, it is a hybrid), it is still incorrect. The Volt has an electric motor and an Internal Combustion Engine (ICE). Simply put, when the cabin demands heat, the heat is supplied by an electric heater. When the ICE is running, it provides the heat, just like your own car. The thermal system of the Chevy Volt is an amazing feat of engineering. It operates in many different modes (think: cold ambiance, electric only vs hot ambiance, electric only, the the ICE). The system is actually bi-directional, the motors and batteries are actually heated OR cooled depending on the conditions.