I'm thinking you might want some actual facts on your real-life question,
and while I admit I didn't read all the group replies, I read enough to see
that several were less than helpful.

There are more than two types of diesel heater - there are those that are
more like fireplaces. These are mounted on an inside bulkhead with a
combination air intake/exhaust pipe to the outside. I've never had a boat
with the wall space for one of these, but I know they can be very effective-
quiet, cozy and nice looking. I've seen some wood burners that get pretty
smoky on deck, but a buddy has a diesel model that is clean and works great.

I have owned and installed diesel forced-air furnaces on two boats - a San
Juan 28 and a J/32. The first was an Espar D3L and the second is a Webasto
AT3500. Both companies also make similar-sized "Hydronic" furnaces that
distribute the heat with hot water, but I have not used one of those. I
chose the forced air models because they are less expensive, and because the
tradeoffs in installation actually favored the air models in my case.
Here's why:

The water models _are_ much easier to route the water pipes compared to the
large hot-air ducts. However, at the point of use (cabin outlets) you need
to install a heat exchanger (aka radiator, Red Dot heater, etc) that is very
large and requires 12V power to run a fan. In both cases that part was
actually harder to fit in tight spaces than the ducting. As another poster
mentioned there is the advantage of being able to route engine cooling water
through the system to provide "free" heat while under way. However, my
forced air furnace works just fine while under way also. One concern I
would have with a complex hot water system (engine, hot water heater,
furnace) is more places where a leak could occur, and losing engine water
can be very expensive compared to losing cabin heat.

Also, both models have the same requirements for combustion air intake and
exhaust air outlet pipes, as well as fuel pumps, fuel line, furnace mounting
and wiring, thermostat location and wiring - in other words lots of things
to install besides the heat distribution. However, your boat may have
different open spaces (or obstructions) that would make the forced-air
models impossible to install. You need to figure that one out.

Now about batteries. My boats have been fine with a pair of group 24s (in
the San Juan 28) and group 27s (in the J/32). I like to stay at anchor for
a couple of days at a time, and by the third day I'm needing a charge,
especially if I run the refrigerator full time. I use Gel batteries, which
are rated at 87 AH, not the typical 105 AH as found with wetted cell
batteries. I cruise in Puget Sound and British Columbia, more in summer but
also often in winter months. The winters here are fairly mild, with
temperatures on the water usually in the 40s or higher. One tradeoff is
that I use the furnace more and the refrigerator less in the winter,
vice-versa in summer. When I use the heater I'm comfortable with cabin
temps around 65*. I did upgrade the alternator to provide a little shorter
charging time, and I would like to add a third battery just for engine
starting so that I can avoid worrying about discharging the two group 27s
beyond the point of starting failure. I do have a good battery charge
monitor so I can keep track of the charge levels.

You can look up fuel and power consumption numbers on these furnaces and
I've found them to be reasonably accurate claims. Don't overlook the fact
that these things do cycle on and off to maintain a temperature, so the
average power/fuel consumption is less than what they say for continuous
running. On my boat on a cold day the furnace will first run continuously
and then frequently until the boat really warms up, which takes a fairly
long time when first going on board. However after several hours the
internal objects, people, etc. store some heat and the furnace doesn't need
to work so hard to keep it comfortable.

I also have an opinion about Espar vs. Webasto, and some experience with the
reliability of each. I'll be glad to share if interested.

Hope this helps!

Don
--
http://www.sailj32.com/
The Unofficial J/32 Owner's Web

"Courtney Thomas" wrote in message
...
I'm told that there are at least 2 types of boat heater, both of which
burn diesel; one using a blower to disperse the heat and the other heating
a circulating liquid.

What are the experiences of the group with both, please ?

Thank you,
Courtney
--
s/v Mutiny
Rhodes Bounty II
lying Oriental, NC
WDB5619