Diesel-Fired Hot-Water
Heaters (Hydronic Heaters)
Again, if your home is heated with water
circulated through baseboard heaters, this
is about the same as diesel-fired hot-water
heaters on boats. Like the hot-air system, a
diesel furnace heats water, and the water
is circulated around the boat to air han-
dlers. Since there is limited room aboard,
these air handlers are usually radiators
(coils of tubing with hot water running
through them) with a blower that more
effectively transmits the heat to the sur-
rounding air. Where there is more space,
radiators without blowers can be installed.
These heater systems are also termed
hydronic heaters. The blowers at the air
handlers should be governed by a thermo-
stat (called an aquastatfor this use), which
prevents the blowers from switching on
until the water in the radiator has become
hot. Without an aquastat, you will get anunpleasant blast of cold air from the air
handler until it warms up properly.
Of course, to increase efficiency and to
eliminate the chance of freezing, the “water”
in these systems is really a water/antifreeze
mix. Since the heat is transferred through
plumbing, the boat can be divided into zones,
each controlled by a separate thermostat, to
get exactly the heat needed in each area. You
can also use a hydronic heater to heat hot
water for the freshwater plumbing, though I
generally prefer to keep the hot-water system
separate for simplicity and redundancy. Still,
if you’re going to live aboard in the winter,
this approach gives you virtually unlimited
hot water for washing and showers when at
the dock. (In the summer, with the heater off,
this naturally is not the case.) In arctic or
near-arctic conditions, you may also want to
preheat the engine. A heat exchanger can be
arranged off the hydronic heater to do this.
Don’t mix the engine coolant and hydronic-
heater coolant directly, however.PART FIVE: VENTILATION, AIR-CONDITIONING, AND HEATING
Figure 15-12.
Typical hot-water
heating system
(Courtesy Espar
Products, Inc.)