My opinion, Diesel heater is the most efficient system for winter heating a boat in the PacificNW when not at the dock.
When in a marina I supplement diesel heat with an electric oil radiator in the V-berth.
I am biased to the Wallas probably because the one I have came new uninstalled in the boat. The install went smoothly and the heat provided is excellent.
There are less expensive models like the Russian built Planar heater.
Planar Diesel Heaters | Diesel Heater For Boats, Trucks & Camper Vans
I can attest to the performance of the one installed in @LeslieTroyer’s Catalina 36. We sailed for 18 days during one of the worst February storms in the past 50 years. That little heater kept us warm, running pretty much 24/7 the whole trip.
The hydronic systems are intriguing.
@Hayden Watson sails out of Whidbey island and installed one that he enjoys. Says that once he plumbed the engine into the system on his Catalina 30 he was able to create a big enough heat sink to get better heat in the boat. A plus the engine is warm and turns over easy on the coldest mornings.
Insulation is your true friend in this challenge. Our boats leak heat like they were made of open mesh screens.
Insulating the ducts, the cabin roof, hull, ports, hatches etc all play a role in trying to retain the heat you create. Once you sealed all the leaks you need to exchange the air to prevent the cabin from raining inside. This means introducing outside cold dry air into the system and venting the moist air out from cooking and just breathing.
The comfort we seek is complicated, but worth the investment to be able to use your boat on the shoulder seasons October thru March. The marina’s and anchorage’s are generally empty. The workers in the marina’s are always amazed to see a boat winter cruising. They are never to busy to help.
