J801X Installation Manual
7
Figure 6. Combustion Air Drawn from Outside
Through an Exterior Wall
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12" Max
12" Max
Furnace
NOTE:
Each opening
to outside must be at
least 1 sq. in. per
4,000 Btuh of total
input rating.
Vent or
Chimney
Water Heater
See
Note
TOTAL INPUT
RATING (BTUH)
MINIMUM FREE AREA
(EACH OPENING)
ROUND DUCT
DIAMETER
40,000 10 in
2
4 inches
60,000 15 in
2
5 inches
80,000 20 in
2
5 inches
100,000 25 in
2
6 inches
120,000 30 in
2
6 inches
140,000 35 in
2
7 inches
160,000 40 in
2
8 inches
Figure 4. Combustion Air Drawn from Outside
Through Vertical Ducts
Inlet Air Duct must
be at least 1 sq. in.
per 4,000 Btuh of
total input rating.
Inlet and Outlet
Ducts must
extend above
attic insulation.
Outlet 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
TOTAL INPUT
RATING (BTUH)
MINIMUM FREE AREA
(EACH OPENING)
ROUND DUCT
DIAMETER
40,000 100 in
2
12 inches
60,000 100 in
2
12 inches
80,000 100 in
2
12 inches
100,000 100 in
2
12 inches
120,000 120 in
2
13 inches
140,000 140 in
2
14 inches
160,000 160 in
2
15 inches
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12" Max
12" Max
Furnace
Vent or
Chimney
Water Heater
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Air Duct
Air Duct
NOTE: Each
opening to
outside must
be at least 1
sq. in.
per 2,000
Btuh of total
input rating.
See
Note
TOTAL INPUT
RATING (BTUH)
MINIMUM FREE AREA
(EACH OPENING)
ROUND DUCT
DIAMETER
40,000 10 in
2
5 inches
60,000 15 sin
2
6 inches
80,000 20 in
2
7 inches
100,000 25 in
2
8 inches
120,000 30 in
2
9 inches
140,000 35 in
2
10 inches
160,000 40 in
2
10 inches
Figure 5. Combustion Air Drawn from Outside
Through Horizontal Ducts
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.
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.
Installation In An Unconfined Space
An unconfined space is an area including all rooms not
separated by doors with a volume greater than 50 cubic feet
per 1,000 Btuh of the combined input rates of all appliances
which draw combustion air from that space.
In general, a furnace installed in an unconfined space will not
require outside air for combustion. However, in homes built for
energy efficiency (low air change rates), it may be necessary
to provide outside air to ensure adequate combustion and
venting, even though the furnace is located in an unconfined
space. See Example.
EXAMPLE
A space with a water heater rated at 45,000 Btuh input
and a furnace rated at 75,000 Btuh requires a volume of
6,000 cubic feet [50 x (45 + 75) = 6,000] to be considered
unconfined. If the space has an 8 foot ceiling, the floor
area of the space must be 750 sq. ft. (6,000 / 8 = 750).
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
1in
2
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,