Which Leaf? The S has resistance heat only, and so uses large amounts of power whenever the heat is on. The SV and SL, though, have a heat pump as well, and until the temps get down below 25F or so will use considerably less. Below about 15F the power consumption is virtually the same for all Leaf models. See my "Tips & Tricks" post, which I will now bump up, for Winter driving tips.
2013 "Brilliant Silver" SV with Premium and no QC, a 2009 Vectrix VX-1 W/18 Leaf modules, and 3 EZIP E-bicycles.
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.