Thanks for the link to the write-up. In the fall of 2016 I installed a fully hydronic system in our 3-cabin Catalina 42. The original forced air Ardic (circa 1990) had never been enough to heat more than the main saloon and was becoming impossible to repair. Like you I suffer of ODIYD (Obsessive DIY Disorder) and had to do it all myself. I rather envy you the engine room space you have on your new boat! I found a new-in-the-box but shelf-worn 15kw (48,000 BTU) Espar boiler on Ebay for $500 and built up the rest of the system myself. Each cabin has it's own radiator coil with two 5 inch PC rack fans. Zone control is by valves that can be shut to the 2 aft cabins that are mostly unused. Because of the limited spaces on a sailboat each fan-coil unit was custom made from 1/4" birch plywood to fit the space. For the coils themselves I found car heater units for 1960's vintage cars. Two different sizes were good for all the units. Also added a circulation pump and heat exchanger to heat the domestic water. The control system was also DIY and is set up so if the engine is running the Espar is turned off the the circulation loop is heated by the engine coolant through another heat exchanger. The whole thing works great! We cruise pretty much year around in the Pacific Northwest. Our main head is in the bow and used to be the coldest part of the boat. Now it is the warmest. My wife loves that!