Reverse-Cycle
Air-Conditioning
We discussed reverse-cycle air-conditioning
previously. Reverse-cycle is simple as part of
the A/C system, but it requires a gen set and is
limited to delivering heat during moderate
temperatures.
Direct Electric Heat
Direct electric heating can make good sense
on large yachts or small commercial vessels.
It’s no different from electric baseboard heat-
ing in a home, though because the heater-
element size is usually smaller, it often re-
quires a blower. Electric heating is efficient,
compact, and easy to install. The drawback is
obvious: It takes a lot of electric power. Un-
less you’re running a boat with a couple of
generators, one of which will be on almost all
the time, it’s not for you.
DO NOT USE FREESTANDING ELECTRIC
HEATERS Though properly designed and
installed marine direct electric heaters are
excellent (when the electric power is avail-
able), never use freestanding electric
heaters—that is, the kind you can purchase
at a local hardware or home supply store.
These heaters are not designed for boats. It
can seem a cheap alternative to add one or
two of these to keep a boat warm when at
the dock, but they are responsible for many
boat fires. Beware!
Diesel or Kerosene
Bulkhead Heaters
Small bulkhead-mounted heaters fueled by
diesel or kerosene can be quite effective and
are inexpensive. Usually they can be fed by a
gravity tank, so no pump is necessary. But if a
gravity tank won’t fit, a small electric pump
can be installed to take off from the main
diesel tanks. (Any tank must meet all the re-
quirements for diesel fuel tanks [Chapter 5],
and NFPA 302 limits independent gravity
tanks for stoves to a capacity of 2.1 gallons or
8 liters.) Output usually ranges from around
3,000 Btu at low heat on a small unit to as
much as 18,000 Btu at high heat on a large
unit. This can warm you most effectively in
even very cold weather. The drawback is that
as you get farther away from the heater, you
get farther away from the heat. A single bulk-
head heater in the main saloon may keep this
area quite toasty, but it will leave, say, an aft
cabin very cold. The trick of running the
chimney through the bulkhead (as mentioned
for coal stoves) can help here. (Check with
the manufacturer for proper fittings and
insulation.) Of course, you can install two
heaters, one forward and one aft in the boat.
This combined with a couple of 12-volt elec-
tric fans can distribute the heat moderately
well.
Some of these heaters use cabin air for
combustion. It is thus vital that there be
proper ventilation to the outside. The larger,
higher-output models have dedicated
combustion-air intake, which is recom-
mended. In addition, ABYC requires an
oxygen-depletion sensor, which will automat-
ically turn off the heater should the oxygen
content of the air in the cabin be reduced to
95 percent of normal levels. These heatersChapter 15: Air-Conditioning and Heating
Figure 15-9.
Diesel cabin
heater (Courtesy
Dickinson)