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In Colours of the wind, a Piper built narrow boat used in Holland as a live aboard, we do have a similar system.
In our case it is also a casing near the floor. Inside the casing are two pipes with fins. Those fins do enlarge the surface of the pipes so they are more efficient in transferring heat to the air.
In our situation this system is doing it's job very well. We don't have any complains, and in winter it is still warm enough.
We also do have a diesel fired Reflex stove in our saloon area.