the leak thing.
You insulate yourself against the problem of leakage by installing a second heat exchanger at the engine. This way, should a leak develop in the heater plumbing, none of the engine coolant is affected. Water heaters are indeed more quiet than forced-ail heaters, but are not exactly silent. We can certainly hear the turbo sound when our Webasto fires up at night, especially in the aft cabin. The main benefits of a water system, in my opinion, are the radiant heat on the sole where the pipes run, plus the ability to heat water for showers while on the hook, and greater diesel/electrical efficiency. The main benefit of the forced air system is that it imports air from outside the boat, making it more effective at drying out the cabin. We heat our 410 with a single radiator in the cabin. The bed in the aft cabin is warmed up by radiant effect. A buddy of mine, by the way, fabricated a towel warmer/dryer in his head by zig-zagging the hot water lines through that area. Oh, by the way #2, another benefit of a hot water system is that the radiator will run off of engine heat while motoring. A nice feature during an all night slog through fog. We installed a toggle so that our system can run off the furnace or the diesel alternately. Having a water system installed is pricy, you can count on upwards of $5000 for a 40+ footer. Lots of plumbing, enough to take a trained installer a full week of labor.