Wow I didn't realize that. That makes no sense for efficiency! (And if true adds evidence to debunk Insightman's engineering optimization theory) But its one factor that helps explain why my winter gas mpg is so much worse than summer. I averaged about 36 last winter, versus a pretty consistent 50 over the summer in similar conditions. Not only would electric heat use up more charge, but it also has to drive the generator harder, which results in less time it can go into efficient gear mode. Of course friction and higher drag snow tires are part of this too. But this all adds up as there were times in winter when the car would not go into gear mode at all on the highway. My 3 series BMW that the Clarity replaced would typically go from 30 mpg in the summer to 27 in the winter, a tiny range in comparison, but of course that car is a lot lower on the efficiency scale.