Cars with water-cooled internal combustion engines generate so much heat that it has to be dumped to the atmosphere via a radiator. Using this "spare" heat to warm the interior with a second radiator inside the car effectively costs nothing. Rechargeable electric cars are now becoming available. These cars are usually of limited range, say 100 miles. They will surely be fitted with heaters. I have never seen any comments in the media on how heating is provided in battery-powered cars. Either the heater would be powered from the battery or a separate liquid or gas fuelled heater. If the former, this could have a significant effect in reducing the range of the car and how much heating you can use if you are gridlocked in a snowstorm?