Heating a gas car is essentially free. Cooling a small car takes about 4 hp off you engine’s rating.
The reason heating a gas car seems free, is that you are just tapping to the tremendous amount of waste heat that the gasoline engine puts out. Of course, all of that heat is generated by gasoline whose energy is not being used to turn the wheels, and you are still paying for that gasoline. Another way to look at it would be that with an electric car, you only use energy to heat or cool when you tell the car to do so, in a gasoline engine, you are burning gas to generate heat, whether you direct it into the passenger compartment or not.