Leaf 2014 owner for 5½ years. It has air PTC and no coolant loop.
It is possible to use air heater but heatpump is good enough. Range reduction usually around 10%.
Though I also bought Mitsubishi iMiEV for fun and it has coolant based cabin heating,
same as older Leafs. Range reduction is massive, 30% below freezing.
So I got used Webasto heater (there are two quality companies AFAIK, Webasto and Ebersprächer).
Took it off an old BMW for 100€.
5kW heating power. Or 2.5kW at half power.
Can't do less heat unfortunately.
Will reduce power at 70*C and switch off around 75*C.
So if you switch it on you have to take the heat
I have access to HVO (renewable "diesel", not the same as biodiesel, but on legal documents it is biodiesel).
It is 100% non-fossil, burns absolutely cleanly and I've used it on my backup ICE car (BMW
It is ultra clean, no smell when starting cold. Excellent startup etc etc.
So I will use that as a fuel for EV fuel based heater. It has infinite shelf life and no smell (it looks and tastes like water/cooking oil).
This fuel is expensive (almost 2€/liter) but as consumption is laughable, I don't care
Exactly 10$ per US gallon. But deem it cleaned my old ICE.
Maybe it is available elsewhere in the world - I would definitely recommend.
PS2: Keep away from FAME (real biodiesel).