Courtney Thomas wrote:
How do the forced air units compare with the hot water ?


The water units are more efficient in terms of amount of fuel burned per
BTU transferred to the cabin air, but they are more expensive and a bit
more demanding to install in most boats. Maybe a wash, unless you want
to put a heater in a space distant from the furnace. Then the hot water
makes sense.


Dennis Pogson wrote:
I would guess that pumping hot water at low pressure through radiators and
associated piping requires a lot less power than forced-air blowing.

Partly that, and partly that water-cooling a combustion chamber picks up
more heat over a smaller area.

... At
least, that is our experience, and the heat is much more evenly distributed.
Also, those areas which didn't need heat were simply turned off, or the
radiator stat was turned low to suit the environment/occupants. The system
is silent, which makes for peace and quiet. Drilling through bulkheads etc.
is a darned sight easier when the holes are merely 1" dia. or less, against
the 3"-4" holes required for air tubing.

True, but you have to provide routing both ways, and insulat the lines.
In our boat, I ended up drilling two 1 1/4" holes thru each space for
the heater lines. Still, that's less area and a bit easier to place, and
can carry more heat than a 4" air duct.



The heating unit is very quick to achieve operating temperature, and for
cold the system started to be effective in about 15 minutes. If an en-suite
radiator is inadvertently left full on, the heads would become a sauna!


That agrees with our experience. Between 10 ~ 15 minutes and the heaters
are hot. Takes a bit longer to warm up the space, but it's marvelous to
be able to warm your hands or feet at the radiator.


Although diesel-fired, our boat seemed to survive the winter on very little
fuel, admittedly, we had 2 * 60 gallon tanks, but the guage never seemed to
move much over winter.


We kept our boat (36' tug) toasty warm thru a NC winter, admittedly not
as cold as some but last winter was long & wet, for about 30 gallons of
diesel... actually that included a few short trips underway, too.

I am completely sold on this form of heating against the forced-air systems.


My wife loves our heater, and that makes it worth everything. IMHO the
forced air ones are easier to install with regard to the main unit and
if routing the ducts isn't a big problem. They pump out the heat pretty
quick. But the fans are noisier (our Webasto heater is totally silent
except for the clicking of the fuel pump, and maybe an occasional
whooshing in the furnace exhaust) and it's most often a problem to route
ducting to say a fore cabin. With the water heater, you can put the
radiators in series and heat several spaces from one loop. With air, you
need ducts to every space. And I've known several boats with toy 2"
ducting for both heat & A/C... not worth the bother, can't get enough
air thru it.

Fresh Breezes- Doug King