Heater selection [Need help - 2]

[wind_magic]

The second important purchase I am considering is a diesel heater, and I know basically nothing about these except that they burn diesel and make heat. I assume there is an outside air intake and some kind of heat exchanger, then an exhaust port and internal fans and such to force the warm air out into the space to be heated. What kind of variables should I be looking at when deciding on a heater, I know I have to do the calculations to make sure it will actually deliver the BTU's for the space, but other than that, what else should I be looking at ? Any suggestions ? I'm mostly looking for a place to educate myself I suppose, I need to learn more about these heaters, but most of the information I have found is vendor specific and doesn't give me much of an overview.

Talking low 30'ish foot boat and I definitely want diesel.

[JomsViking]

Espar heaters are pretty good forced air heaters. If you want a heater that uses no electricity have a look at these:
DickinsonMarine.com - Marine Heaters, Stoves and Barbeques or Frontpage - Refleks Olieovne A-S - Ringe
I have a Refleks, and like it. The Dickinson is a little prettier to my eyes, but both are effective.

[sailak]

The Espar forced air heater in my 36 footer does a great job.

[sailingdog]

A lot of this depends on what level of complexity you want to get into. There are forced air systems, like the Webasto and Espar, and there are stove like heaters, like the dickinson. Both types work, but the forced air systems are probably a lot more work and more complicated to install. YMMV.

[Sequitur]

I have an Espar hydronic unit in my boat that has kept me toasty for the past two winters. It has the added advantage of being able to heat my hot water if I so choose, with or without heating the boat.