This is a little out of my normal bailiwick. I have an unfortunate amount of personal experience.
Most of the forced-air heaters cut back on fan speed once the boat reaches a steady temperature. For weekend use that's fine. For liveaboard
application it doesn't work so well.
I had to do three complete rebuilds on a Webasto in four years. I replaced the Webasto with an Espar and have had a much better experience.
After lots of time on the phone
with Webasto (in the US and Germany
, limping along with high school
German) and Espar (US only) I learned a lot. What I was told aligns with my experience. I had no issues with performance in Europe
. Both companies said that US diesel
was a problem, exacerbated by liveaboard
As the fan is stepped down combustion efficiency declines which leads to carbon build-up in the combustion chamber. The Webasto is tougher to rebuild
. In addition it easier to get an Espar to recover without a rebuild
Running a gallon of kerosene (based on recommendations from Webasto, Espar, and two different technicians at two companies that work with both Espar and Webasto) through the heater every four to six weeks has really helped to keep the combustion chamber clean in continued liveaboard use.
I don't have enough data to reach deterministic conclusions. Based on my experience, I'll buy Espar over Webasto, plumb in a one gallon kerosene tank with a Y-valve into the main diesel
tank, and turn the heater down or off when I leave the boat so it runs full on when I turn it back up.