My 2013 FFE's indicated range is computed from my past 3 Ts (Technique, Terrain, and Temperature) based on the previous 20 charging sessions (fewer if some variable is changing rapidly). If I used much cabin heat, or Max Defrost (which turns on a/c and cabin heat and fan, all at max), the car would quickly learn to knock 20+ miles off my predicted range.
However, on a ~25˚F day in the driveway here at 7100' in the Colorado Rockies, I just made some observations using the Accessories option in the MyView display (I'll try next to post as a new topic how I set up that screen):
- Fan, from lowest to highest speed. uses from <0.1 to 0.3 kW of "Other" load.
- Max Defrost uses 2.1 kW, so an hour of that uses up about 11% of a full nominal charge.
- Low fan plus 65˚F Auto cabin heat varies between ~0 and 1.0 kW as cabin heater cycles on off, but at 60˚F, <0.1 kW.
- Low fan at LO temperature setting, which seems to me ≤59˚F, uses <<0.1 kW (and zero indicated power for Climate, i.e. cabin heater is off).
- Setting to low fan and LO temperature, vs 65˚F Auto, immediately raised my predicted range by 9 miles.
Front-seat heaters reportedly draw up to 0.5 kW at max "5" setting (too hot for most people—I like 1–2), but apparently are powered by the 12VDC accessory battery. Perhaps someone knows how much and how often and by what algorithm this is recharged by the DC-DC converter from the main traction battery, but in the short run the seat heaters seem not to show up as a traction load that affects range. However, the a/c and cabin heater are high-voltage and hence directly reduce range.
So for max winter range, I suggest preheating cabin with Remote Start set to max 15-minute duration, and repeated once if necessary, while the car is still plugged in, then defrosting with bottom-row (not Max) defrost button at LO temp (outside air) and min fanspeed.
If your side windows fog up or frost over, the owner's manual has a nice tip: press floor-vent and panel-vent air distribution buttons in bottom row of center panel, select a/c, adjust temp control for comfort, set fan to max, and direct outer instrument-panel vents toward side windows while closing vents in middle of panel.
The main winter range-saver, given good driving technique, is to minimize use of the resistive cabin heater by relying instead on seat heaters and clothing. That is, set cabin temp to LO (≤59˚F) if you can, otherwise as low as comfortable. (You will lose significant range if you set to a normal indoor house temperature rather than wearing winter clothing!) Defrost using the bottom-row defrost-and-person button, which is the "vent" setting other users have wanted, i.e. it admits outside air. Then the next need, as a much lower priority, is to use the lowest fanspeed consistent with avoiding windshield/window fogging. If you set fanspeed manually or on the center touchscreen, it will retain that fanspeed setting even if you turn ordinary defrost off and on (not if you Max Defrost, which locks fanspeed to max while activated) or if you turn the car off and on, but it will lose the fanspeed setting if you turn the whole Climate panel off and on.