Diesel heaters, like the Dickinson (DickinsonMarine.com - Diesel Natural Draft Heaters
) or Refleks (Outline for installation - Refleks Olieovne A-S - Ringe
) are vented, but SD is right that you need to preheat them. You can, however, do that with tabs or strips, so that you do not have to fiddle with alcohol in a rolly anchorage. But I have to agree that the propane stove is efficient and clean.
Btw. I just love my Refleks heater, it makes a very large difference on a cold and/or wet day + it uses no electricity at all.