J952V Installation Manual

8
Outdoor Air Using Vertical Ducts
If combustion air is taken from outdoors through vertical
ducts, the openings and ducts must have a minimum free
area of one square inch per 4,000 Btuh of total appliance
input. See
Figure 4.
Outdoor Air Using Horizontal Ducts
If combustion air is taken from outdoors through horizontal
ducts, the openings and ducts must have a minimum free
area of one square inch per 2,000 Btuh of total appliance
input. Ducts must have cross - sectional area at least as
large as the free area of their respective openings to the
furnace space. See
Figure 5.
Air Directly Through an Exterior Wall
If combustion air is provided directly through an exterior
wall, the two openings must each have free area of at least
one square inch per 4,000 Btuh of total appliance input.
See
Figure 6.
Alternate Method of Providing Air from Outside:
If acceptable under local Codes, it is permitted to provide
outside air using one opening (See NFGC). Generally,
confined spaces must have 2 openings in the space for
combustion air. One opening must be within 12 inches of
the ceiling, and the other must be within 12 inches of the
floor. However, an alternative method recently adopted by
the NFGC uses one opening within 12 inches of the top of
the space. This method may be used if it is acceptable to
the local codes.
THE FOLLOWING CONDITIONS MUST BE MET:
1. The opening must start within 12” of the top of the structure
and connect with the out of doors through vertical or
horizontal ducts or be ducted to a crawl or attic space that
connects with the out of doors.
Figure 4. Combustion Air Drawn from Outside
Through Vertical Ducts
TOTAL INPUT
RATING (BTUH)
MINIMUM FREE AREA
(EACH OPENING)
ROUND DUCT
DIAMETER
38,000 10 sq. In 4 inches
60,000 15 sq. In 5 inches
80,000 20 sq. In 5 inches
100,000 25 sq. In 6 inches
120,000 30 sq. In 6 inches
140,000 35 sq. In 7 inches
160,000 40 sq. In 8 inches
Air Duct must be
at least 1 sq. in.
per 4,000 Btuh of
total input rating.
Ducts must
extend above
attic insulation.
Air Duct must be
at least 1 sq. in.
per 4,000 Btuh of
total input rating.
Ventilation Louvers
at each end of attic
Attic
Insulation
12" Max
Furnace
Water
Heater
Vent or
Chimney
Figure 5. Combustion Air Drawn from Outside
Through Horizontal Ducts
TOTAL INPUT
RATING (BTUH)
MINIMUM FREE AREA
(EACH OPENING)
ROUND DUCT
DIAMETER
38,000 20 sq. In 5 inches
60,000 30 sq. In 6 inches
80,000 40 sq. In 7 inches
100,000 50 sq. In 8 inches
120,000 60 sq. In 9 inches
140,000 70 sq. In 10 inches
160,000 80 sq. In 10 inches
Furnace
Water
Heater
Air Ducts must be
at least 1 sq. in.
per 2,000 Btuh of
total input rating.
Vent or
Chimney
Air Duct
Air Duct
TOTAL INPUT
RATING (BTUH)
MINIMUM FREE AREA
(EACH OPENING)
ROUND DUCT
DIAMETER
38,000 10 sq. In 4 inches
60,000 15 sq. In 5 inches
80,000 20 sq. In 5 inches
100,000 25 sq. In 6 inches
120,000 30 sq. In 6 inches
140,000 35 sq. In 7 inches
160,000 40 sq. In 8 inches
NOTE:
Each opening to outside
must be at least 1 sq. in. per
4,000 Btuh of total input rating.
12" Max.
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Furnace
Water
Heater
Vent or
Chimney
12"
Max
See
Note
See
Note
Figure 6. Combustion Air Drawn from Outside
Through an Exterior Wall
2. The opening must have a minimum free area of 1 in
2
. per
3,000 Btu per hour of the total input rating of all equipment
located in the enclosure.
3. The free area must not be less than the sum of all the
areas of the vent connectors in the enclosure.