I have followed this threat with some interest and I think I can add a little information, since my experience with diesel/kerosene heaters goes back to the 50s and several boats, both sail and power. The German Webasto/Espar heaters were originally designed as "bus heaters", particularly to heat passenger trailers used behind commuter buses back in the 50s, as well as augmenting engine heat in buses when needed. As far as I know, they all operate off thermostats. That means every cycle starts with a power hungry glow plug sucking 12 to 20 Amps, at around 3x/h = 24x in the course of a cold night. That's enough to totally flatten a good sized battery. And when the heater runs, the fan, fuel pump, and electronics also needs power. Additionally, the decline in temp before the heater comes on again is quite noticeable. Setting the thermostat for a smaller difference = more cycles = more power consumption = not a good situation on a boat with limited battery capacity. (We had a Webasto on an Islander 30.)
Wallas designed their heaters for small off grid cabins and saunas popular in Finland. We installed a 30D (diesel) on our IP 380. It did not have a thermostat circuit. Instead, you regulated the output with a simple rheostat knob, which in turn regulates both the fan and the fuel pump/fuel flow. It, too, starts ignition with a glow plug, but only once. You then set the output and it burns/heats at that rate, which typically is under 1 Amp. Carl, then owners of Scan Marine, showed us how to de-carbon the little furnace, but it performed flawlessly for the 3 season we lived on the boat full time and I never touched it after installation. I would install another Wallas over either Webasto or Espar in a small boat, because of good experience, much lower power consumption, even warmth, and much less complexity. The W. furnaces have 2 output pipes for hoses, which should be vented as low into the cabin as practical, as pointed out above.
We are now on our 3rd Wallas in the CC-23. So far, I have not found any of them to not function well. I was concerned about the installation in the CC-23 above the fridge, with no vents in the cabinet. Electronics don't like heat. I installed a vent in front over the fridge, and one on top behind the stove, to create air flow, which should have been done in the factory. This Wallas is a kerosene stove, which works very well to cook on. Again as pointed out above, its value as a heater is deminished because the warm air comes out at waist level, leaving the footsies cold. It still adds greatly to comfort and drying a small boat on colder or rainy days, and is a decent compromise if you bring warm socks. For glacier cruising, I would add the W. 30D.
Al (HARMONY)