In reply to MarkJH:
> The only other comment I can think of is that they both have relatively high current draw. I took one out (of a boat) a few years back and was thinking about reinstalling it, but the current draw on start up was around 6A, and 1-2A during use. A few years ago, this didn't seem much, but these days, with LED lighting and affordable wind/solar it becomes a very large proportion of the daily usage, and I have gotten used to not needing the engine for charging at all. I am now considering whether I actually need a forced air heater or whether a naturally vented diesel or solid fuel heater might not be more useful. Probably this will depend on how you use the van and the outside temperatures you are expecting to deal with.
> I guess another way to look at it would be that a reasonable sized (100-200 Ah) domestic battery bank has far fewer demands on it now than it used to, so why not use the spare amps for heating.
They do indeed, probably the second biggest problem we had with them was the voltage cut-offs would turn them off (the biggest problem is they lie idle for eights months of the year and then the fuel in the burner and pipes is so old they takes about 100 attempts before they start properly and don´ t fill the boat with stinking diesel smoke). Air systems have their attractions but pushing the air around is power-hungry (and the ducting a pain to install). Hot-water systems are far better but normally we´ d only fit them on 20-25m yachts though some of the Scaandinavian companies like Vindo used them even on the smaller yachts down to 8m. Quieter as well!