8. Mechanical Combustion Air Supply:
a. In installations where all combustion air is
provided by a mechanical air supply system, the
combustion air shall be supplied from the
outdoors at the minimum rate of 0.35 ft3/min per
1000 Btu/hr (0.034 m3/min per 1000 W) of the
total rated input of all appliances in the space.
b. In installations where exhaust fans are installed,
additional air shall be provided to replace the
exhaust air.
c. Each of the appliances served shall be interlocked
to the mechanical air supply to prevent main
burner operation when the mechanical air supply
system is not in operation.
d. In buildings where the combustion air is provided
by the mechanical ventilation system, the system
shall provide the specified combustion air rate in
addition to the required ventilation air.
9. Louvers & Grills:
a. The required size of openings for combustion,
ventilation, and dilution air shall be based on the
net free area of each opening.
i. Where the free area through a louver or grille
is known, it shall be used in calculating the
opening size required to provide the free area
specified.
ii. Where the free area through a louver or grille
is not known, it shall be assumed that wooden
louvers will have 25% free area and metal
louvers and grilles will have 75% free area.
iii. Non-motorized dampers shall be fixed in the
open position.
b. Motorized dampers shall be interlocked with the
equipment so that they are proven in the full open
position prior to ignition and during operation of
the main burner.
i. The interlock shall prevent the main burner
from igniting if the damper fails to open during
burner startup.
ii. The interlock shall shut down the burner if the
damper closes during burner operation.
10. Combustion Air Ducts:
a. Ducts shall be constructed of galvanized steel or
an equivalent corrosion-resistant material.
b. Ducts shall terminate in an unobstructed space,
allowing free movement of combustion air to the
appliances.
c. Ducts shall serve a single space.
d. Ducts shall not serve both upper and lower
combustion air openings where both such
openings are used. The separation between ducts
serving upper and lower combustion air openings
shall be maintained to the source of combustion
air.
e. Ducts shall not be screened where terminating in
an attic space.
f. Horizontal upper combustion air ducts shall not
slope downward toward the source of the
combustion air.
g. Combustion air intake openings located on the
exterior of buildings shall have the lowest side of
the combustion air intake opening at least 12
inches (305 mm) above grade.
11. Refer to Section 3 of this manual, Venting & Air Inlet
Piping, for specific instructions for piping the exhaust
and combustion air.
6
PREINSTALLATION
Do not install this boiler where gasoline or other
flammable liquids or vapors are stored or are in use.
WARNING
This boiler is certified as an indoor appliance. Do not
install this boiler outdoors or locate where it will be
exposed to freezing temperatures.
WARNING
Do not install this boiler in the attic.
WARNING
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