Looked at my very limited amount of J.Falk data here, and didn´t find anything.
Would make sense theugh, as i only have some German info here, which most likely wouldn´t list an exportengine like that.
However, of the top of my head, i would consider it pretty unrealistic that they did.
Nomatter how it was set up, a firebox would radiate way to much heat, to stay within the normal comfortzone temperaturewise, when it comes to electric wiring.
(Unless incredibly well insulated with asbestos or similar of course.)
Would love to be otherwise educated though, do you have such an engine Tom, since you´re forwarding the question here?