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

Ventilation for Heaters

It’s often overlooked that cabin heaters that

burn fuel need additional ventilation. When a

cabin heater is installed in a cabin—a heater

that burns fuel (not an electric heater)—you

have to allow additional vent area to provide

for its combustion and avoid a buildup of

carbon monoxide and carbon dioxide.

Formula 16-1. Determining Adequate

Ventilation Area for Fuel-Burning

Heaters

For unflued heaters

Vent Section Area, sq. in.= Btu/hr. ÷ 1,000

Vent Section Area, cm^2 = Btu/hr. ÷ 155

For flued heaters

Vent Section Area, sq. in.= Btu/hr. ÷ 5,000

Vent Section Area, cm^2 = Btu/hr. ÷ 775

Where

Btu/hr.= Btus per hour of heater output

(Btu, British thermal units)

(To convert watts to Btu/hr., multiply

watts× 3.415)

Theflueis a dedicated duct for taking

air directly into the heater’s combustion

chamber from the outside. It is not to be

confused with the chimney, which expels

the exhaust gases.

Example: Let’s say we installed a 6,000

Btu/hr. flued diesel cabin heater mounted on

the bulkhead of the main saloon of our

example boat,Ocean Breeze. We would then

need to install

6,000 Btu/hr. ÷ 5,000= 1.2 sq. in. vent area

or

6,000 Btu/hr. ÷ 775= 7.74 cm^2 vent area

Accordingly, add 1.2 to 2 square inches

(7.74 to 13 cm^2 ) of vent area to the vents you

would install in this area for the occupants

only.

If you install a central heating system,

say, a diesel-fired hot-water heater system

(hydronic heating), the compartment with

the furnace or burner would need to be ven-

tilated accordingly. A flued 30,000 Btu unit

would require 6 sq. in. (40 cm^2 ) of vent area

added to the compartment, above and

beyond the vent area determined by either

the number of passengers, by the volume

change rate (VCR) requirements for that

area, or by the vents that are required for an

engine.

CHAPTER 16

Ventilation of Machinery

Spaces

Formula 16-1.