Dave Gerr - Boat Mechanical Systems Handbook-How to Design, Install, and Recognize Proper Systems in Boats

Note that either location can blow hot

exhaust onto a dock or a nearby boat,

depending on how you are moored. The

exhaust is noisy and should be fitted with a

silencer provided by the manufacturer. As

always, you must very carefullyconsider

avoiding any exhaust getting back aboard

the boat, since carbon monoxide poisoning

can be deadly.

The combustion intake air demand is

large for these central-heating systems. They

mustbe set up to take their combustion air

from outside the boat.

How Much Heat?

To approximate the total heating capacity

required, you can use the same formula used

to estimate air-conditioning capacity based

on boat displacement in tons (Formula 15-1).

To more exactly determine the required

heating capacity, measure the net volume in

cubic feet or cubic meters of each compart-

ment to be heated. Note the netvolume, in

this case. This is the same concept as the net

volume of engine spaces in Chapter 16. In

this regard you subtract the volumes of built-

in cabinets, bunks, settees, and so on from

the total volume of each cabin. Determine

your intended cruising ground and type of

use, and then multiply the appropriate Btu

per cubic foot or per cubic meter factor from

Table 15-1.

As with most such things, installing too

large a heater is wasteful and inefficient.

Don’t simply install a huge unit; rather, stick

to the recommended output capacity from

the Table 15-1. Note that boats intending to

cruise cold and arctic waters should also

have extensive cabin insulation (not a bad

idea for any vessel). Without this, no cabin

heater can keep up with the demand. Even

worse, the resulting condensation will result

in rivers of water running down the cabin

walls and into the bilge. The resulting cold,

dank, soggy environment can be literally

sickening.

Thoughts on Heating and Air-Conditioning Installations

A small boat with good natural ventilation

and a small bulkhead cabin heater (or a coal

stove) has very little in the way of climate

control or HVAC (heating, ventilating, and

air-conditioning systems). Installing full air-

conditioning and central heating is complex

and requires a lotof ductwork, plumbing,

wiring, controls, blowers, distribution boxes,

grilles, and more. These all take up space and

require maintenance. A large boat that will be

fitted with full split direct-expansion air-

conditioning and hydronic hot-water heating

has two complete and separate systems,

plus the required natural ventilation. You

must make allowance for the space and

weight of all these systems. You must also

arrange for all this equipment to be accessed

for inspection and maintenance. This is not

PART FIVE: VENTILATION, AIR-CONDITIONING, AND HEATING

TABLE 15-1.REQUIRED HEATING CAPACITY

Early Spring Year-Round Use

Through Late Fall Winter Cruising Liveaboard

Cruising Ground Btu/cu. ft. Btu/m^3 Btu/cu. ft. Btu/m^3 Btu/cu. ft. Btu/m^3

Warm Climate 7 247 8 283 9 318
(Caribbean to South Carolina)
Moderate Climate 9 318 10 353 11 388
(North Carolina to Maryland)
Temperate Climate 11 388 12 424 13 459
(Delaware to Massachusetts)
Cold Waters 14 494 15 530 16 565
(Maine to Nova Scotia)
Arctic 19 671 20 706 21 742