The auxiliary heating option uses a Webasto oil-fired burner, with a heat exchanger and circulating pump. It has a remote and a timer (sometimes optionally). While Webasto makes both diesel and gasoline versions, BMW has only ever offered the diesel version. Lots of details are available on the Webasto site. I haven't used them for awhile, so a caution that they may be offering different versions now than in years past. Webasto heaters are common on diesel powered heavy equipment, trucks, and generator sets, particularly in places where you get those sorts of temperatures. Lots of buses used them as well. Having lived in -40, we used quite a few.

The BMW option does use the battery, but only for the circulating pump and control power, not for heating. I imagine that there is a cutoff so that you don't kill your battery completely.

It will be interesting to see what the effects of very cold ambients are on BMW diesels when they arrive. Perhaps some of our Nordic members could comment. In Canada, #2 diesel gells at about -10 C. It literally turns into a semi-solid that you can form into slush balls. It does not go through fuel pumps. It is commonly thinned out with #1 (stove oil) to handle lower temperatures. #1 is not as oily as #2. The issue with high-tech injectors is that some designs have experienced problems with the winter fuel due to the lower lubricity of the fuel. This results in stuck injectors. I don't know if this has happened with BMW diesels, but I am sure we will find out.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue