I've had two diesel
furnaces installed professionally--one hydronic and one forced air--and my experience both times is that the installer was more interested in ease of installation
than in maximizing the capabilities of the boat's heating system. For this reason I would encourage you to design your system first, and then take bids accordingly.
The biggest issue will be where to run the lines. Before installing my hydronic system a friend advised me to install the lines down the center of my saloon
because they would provide radiant heat to the floorboards. I insisted on this with the installer despite his insistence that this would require hours of extra labor. The result, however, was fabulous; on a frosty morning you could walk barefoot from bow to stern and your feet would enjoy the heated cabin sole
. It was easily worth an extra $200. However, to get the boat done the way I wanted it done, I had to finally tell the installer that it was my way or the highway.
I had similar issues regarding the engine heat exchanger
, a pump toggle, and the expansion tank. In each and every instance, the installer argued against how I wanted the system to work in favor of what would be easiest for him to get the job done.
My advice: figure out the way you want it done, and then don't allow the installer to talk you into an easier install. If my experience taught me anything, it's that the installer's convenience was a greater factor in the advice he gave me than any sense of getting my boat's system right.