> more sense to have an auxiliary diesel heating system. This would be much more effective than electric heating and likely generate less carbon emissions

Is this true? Honest question. My understanding is that for cars in general (implicitly driving range), electric cars are lower impact on the energy grid as a whole (ignoring last mile) because of how energy intensive oil is to refine.

Is it that diesel specifically is less energy intensive because of how it differs in refinement to petrol? Or is it that because heating is effectively 100% efficient it doesn't matter that you're using the energy in refinement?