Ellokomotiver med dampvarme? (Generelt)
An alternative was the use of a "Heizwagen":
http://bdw002.privat.t-online.de/868/868-41-heizwagen.htm
I know the Dutch railways used some of those (some second hand from
the German railways) to use the new electric locomotives with the
older coaches that did not have electric heating.
Niels