through the house in air ducts. On a boat, a
diesel furnace (located in the machinery
space, or lazarette, or other compartment
well separated from the accommodations)
heats the hot air, which is distributed by a
blower (usually 12-volt) through the boat via
ducts.
Hot-air heaters such as this may be the
most common on midsize vessels. There’s no
need to find space for a bulkhead cabin
heater, and because the hot-air ducts are
relatively small (4 or 5 in. or 100 to 125 mm
dia.) several delivery grilles can be installed
throughout the accommodations to ensure
even heat distribution. The heater’s workings
are largely out of sight and out of mind—like
your home-heating system. Typical outputs
range from around 6,000 Btu for small units
to 40,000 Btu for large units.
Hot-air heating is not as efficient as hot-
water heating, however, so it’s not as satisfac-
tory in really cold weather. Though 4-inch
(100 mm) ducts are relatively small, they still
take up space and can be awkward to fit in
tight spaces. Also, the blower in the heater
produces a noticeable dull roar, which can be
unpleasant if it’s not installed in an insulated
compartment far enough from the accommo-
dations. Diesel-fired hot-air systems are a
good solution for boats up to about 45 feet
(13.7 m) that are not going to be used in
extremely cold weather.Chapter 15: Air-Conditioning and Heating
Figure 15-11.
Hot-air heater
(Courtesy Espar
Products, Inc.)