I'll weigh in with a recommendation for the Espar Airtronic 4. This one replaced a D4L which while a good heater gave up the ghost and it was simply not a smart idea to throw good money
I did the original install which requires finding paths for 3" Ø flexible ducts an exhaust
hose to the transom in my case... and fresh air for the combustion air. The install is pretty much plug
and play after working out where to mount and run everything.
The Airtronic 4 is a pleasure - quiet and low amp draw especially when it get the cabin up to design temps and then it goes very quiet. The heat is even and dry and it has a fuel pick up from the main diesel
tank so there is no additional fuel source to worry about.
Love the heater and it's high tech monitors gives me a sense of safety
. I'd still recommend that you have a CO monitor
or let some fresh air in. The oxygen is drawn from outside so that a good feature as well. The heat comes up very fast.
There's nothing not to like here... it takes up only unused real estate in my case under the aft berth. It's quiet, clean and heats.
The newer model is far superior to the D4L.