We haven't been below zero, but my commutes this week until today were 0-10*F with windchills down to -18*. But today... A Heat Wave... 15-20*!!!
The heater performs very well, even when it's down to zero. Along w/ seat heaters--

ahhh.
What worried me when starting at 0-5* was the sluggish starter. I wasn't sure it was going to get me going.
And the decreased MPG performance-- I'm heading to an all-time low average. I'll know when I fill again this weekend, but I only clicked 75 miles in the first 3 bars, and now up to 200 miles using 6 bars of guzzle.