7
Figure 4. Combustion Air Drawn from Outside
Through Horizontal Ducts
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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 sq. In
5 inches
60,000
15 sq. In
6 inches
80,000
20 sq. In
7 inches
100,000
25 sq. In
8 inches
120,000
30 sq. In
9 inches
140,000
35 sq. In
10 inches
160,000
40 sq. In
10 inches
Figure 2. Combustion Air Drawn from a Crawl
Space or Vented Attic
Attic
Insulation
Crawl Space
Ventilated Louvers for
unheated crawl space
Inlet air duct must be at
least 1 sq. in. per 4,000
Btuh of total input rating.
Outlet air duct must be
at least 1 sq. in. per
4,000 Btuh of total
input rating. Must
extend above attic
insulation
Water
Heater
Furnace
Vent or
Chimney
Ventilation louvers
at each end of attic
Figure 5. 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 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
Figure 3. 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 sq. In
12 inches
60,000
100 sq. In
12 inches
80,000
100 sq. In
12 inches
100,000
100 sq. In
12 inches
120,000
120 sq. In
13 inches
140,000
140 sq. In
14 inches
160,000
160 sq. In
15 inches
The openings shall exchange directly, or by ducts, with
the outdoor spaces (crawl or attic) that freely exchange
with the outdoors (Figure 2).
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. In installations drawing combustion air
from a ventilated attic, both air ducts must extend above
the attic insulation (Figure 3).
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 (Figure 4).
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 (Figure 5).
Summary of Contents for G7XA Series
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