Just chiming in that we love our diesel
heater. It keeps the cabin
quite warm, and uses maybe 1 gallon a day (if on all or most of the day). We have it fed through a gravity tank that I fitted a through deck
cap for. In the winter, that means every week or so I'm on deck
pouring a gerry can in.
Works underway although (and this is weird) when the staysail is raised or doused it somehow causes the wind
to go down the wrong pipe or something and puts the heater out. Smashing along in force 7 for a day with down pours, no problem. Put the staysail up in the harbor, heater goes out. Weird.
But anyway, it works like a champ.
If you just need to take the chill off in the evening, a kerosene oil lamp
will help with that too. They put out a decent amount of heat.