Our boat came with the Espar. I replaced the old unit (was new when the boat was originally commisioned) with a new one and rewired as recommended by the dealer. The new unit came with the larger wire, thermostat, fuel pump. Fuel is drawn from the main fuel tank.
I would recommend the Espar or similar forced air furnace to anyone in the cooler climates needing a warm cabin. It is very dry heat and you just have to flip the switch on and she does her thing.
One register is in the v-berth and one in the main cabin. The outside temp and inside on Jan 6th for our frostbite race was 38 degrees F. It took about an hour to bring up the cabin temp to 65 degrees F.
In the Spring and Fall when we are out on the hook or at the dock, we just turn the unit on before bed time and during the night if the temp goes down, the furnace automatically comes on and maintains temp.
The thermostat is not calibrated in degrees but it doesn't take long to fine the right setting for your comfort level. We have never turned it up more than about 1/3. Well, we did once, right after I installed the new unit. Woke up in the middle of the night in an 80 degree sweat.
The unit can handle more registers. Would like to pipe in one to the head. But with the furnace, main trunk line on the starboard, I would have to somehow pipe under the v-berth to port where the head is. Big job, lazy captain!
I don't have a good grip on the fuel usage. But they are known to gobble a bit. Not an issue for us as we are on a large inland lake and I just make sure we have enough diesel in the tank for a long outing. Same with electrical power, we just run the m25 for a bit if the batteries are getting low. It does have an automatic shut down at some point if the power gets low.
All in all, very happy with ours. Spoiled sailors we are.