FIG. 5 Combustion Air Direct from Outside
1. If air is taken directly from outside the building
with no duct, provide two permanent openings:
a. Combustion air opening, with a minimum free
area of one square inch per 4000 Btu/hr input
(5.5cm
2
per kW). This opening must be located
with in 12" (30cm) of the floor.
b. Ventilation air opening, with a minimum free
area of one square inch per 4000 Btu/hr input
(5.5cm
2
per kW). This opening must be located
with in 12" (30cm) of the ceiling.
FIG. 6 Combustion Air Through Ducts
2. If combustion and ventilation air is taken from
the outdoors using a duct to deliver the air
to the room where the appliance is installed, each of
the two openings should be sized based on a
minimum free area of one square inch per
2000 Btu/hr (11cm
2
per kW).
FIG. 7 Combustion Air from Interior Space
3. If air is taken from another interior space that is
adequately ventilated, each of the two openings
specified above should have a net free area of one
square inch for each 1000 Btu/hr (22cm
2
per kW)
of input, but not less than 100 square inches
(645cm
2
).
FIG. 8 Combustion Air from Outside Single Opening
4. If a single combustion air opening is provided to
bring combustion air in directly from the outdoors,
the opening must be sized based on a minimum free
area of one square inch per 3000 Btu/hr
(7cm
2
per kW). This opening must be located
within 12" (30cm) of the ceiling.
5
